text:
Talk:Thuringia

Meiningen's population wrong
According to Meiningen's wiki page it has only 21,423 inhabitants (2011). It certainly wasn't higher than 40,000 in 2005. Gearstick (talk) 15:58, 18 February 2013 (UTC)

the modern state of Thuringia was enlarged in 1946. With what? Erfurt and Schmalkalden came to Thuringia already in 1944. I can't find anything else. Fransvannes 15:40 Feb 13, 2003 (UTC)

 * Thuringia (and the neighboring state of Saxony) was also the major "stomping-ground" of the family of composer Johann Sebastian Bach. Sources indicate that the Bach family returned to this area after residing in provinces which lay much farther East. There were supposedly contact with Hungarians and other Eastern Europeans.

In my own experience: My father's family also came to Bavaria (Nuremberg) via Thuringia and Saxony. Our family name is Weissflach, but there were other variations which were consistent with a migration from the East - the same route followed by the Bach family as it returned to its roots from further East. Variations of the name may be found on graves in Leipzig, Dresden and Chemnitz. Some of the variations: Weiszflug (a somewhat Slavic spelling, with the "z"), Weissflug, Weisflog and others.

In ancient times, the Scythians migrated into this part of Europe, orginating from the Caucasus Moutains near the Black Sea. Upon reaching Europe, the migration of Scythians split near the region which is now Poland. One branch went North into Poland and Scandinavia. The other branch spread West, terminating in Thuringia. The genome of the Scythians may have permeated and assimilated into the later Germanic peoples of the region quite directly.

The city of Gera in Thuringia has an ancient past; The city appears in an atlas of Greek & Roman influence in ancient Europe - but no other towns appeared on the map of that time-period. Gera was represented almost as an outpost. It was the farthest and most remote city on the map, but of course this only represented Greek & Roman influence.

The name Gera is not German. Suspecting a Roman influence, I looked up the word in Latin, but this produced null results. Next, I looked up the word in a Greek dictionary: G=Gamma, E=Epsilon, R=Rho, A=Alpha... I found a word which was virtually identical. Gera means similar to "prize" or "privilege". It would seem then that my assumptions were in fact somewhat true about Gera being an outpost. It would also seem to fit the name, insinuating that the settlement of Gera was privilege of sorts, perhaps as the result of a treaty between the newcomers and the resident Frankish tribes of Thuringia. -F.J. Weissflach; 06.01.2004-

 * What means this? I live in Gera, wrote an article about ist history and never heard of such stuff. Gera - a Greek word? I know that the name is quite old (before the Slavic immigration) but I alwais heard it came from the Germanic Ger Aha = "wedge river" or "scree river"! Gera ... Greek ... The atlas you speak of ... is it old or new? --slg 19:09, 14 Jun 2004 (UTC)
 * PS: 1) Why do you call Gera a "small city" - it has more than 100,000 inhabitants! 2) Kann man Deutsch mit dir reden? --slg 19:09, 14 Jun 2004 (UTC)

I've merged in Saxon Duchies
An anon wrote an article, Saxon Duchies which I've merged into the text of the history section of this article. It includes a list of the duchies, which is slightly different than the list currently in the article. Someone knowledgeable about the subject needs to fix this. JesseW 05:44, 3 Dec 2004 (UTC)

 * I'm not an expert, but I've been doing some research, and just created an article for Saxe-Weimar (pre-Saxe-Weimar-Eisenach). I hope to also create articles for Saxe-Eisenach and Saxe-Jena.  I made the spelling of all the Saxon duchies consistent on 'Saxe-', and added links to their articles for the ones that were not already linked.  The Saxon duchies were a rather fluid set of territories belonging to the extended Wettin family that were divided up and re-combined repeatedly, so that, to me anyway, it is very difficult to give a coherent account of their histories. - Dalbury 17:23, 17 October 2005 (UTC)

 * Someone kindly linked my Saxe-Weimar article to the German and Spanish equivalents. There is a great deal of material on the Ernestine (Saxe-) duchies in German and Spanish.  I'll start with the Spanish version, as my Spanish is better than my German. - Dalbury 19:35, 17 October 2005 (UTC)

 * I fixed it up a bit. I removed Schwarzburg and Reuss from the list of Ernestine Saxon duchies, since they didn't belong to those -- they just happened to be in the same general area. If anyone wants a complete list of the Ernestine duchies, there is one at Ernestinische Herzogtümer. --Chl 14:52, 26 October 2005 (UTC)

Polish flag
what's with the polish flag? has this been vandalised? —Preceding unsigned comment added by 86.133.188.33 (talk) 18:36, 3 November 2007 (UTC)
 * NO, Thuringian flag looks like Poland's flag —Preceding unsigned comment added by 84.164.240.26 (talk) 19:13, 23 February 2008 (UTC)

Hitler's Bomb
I added quite a bit of context to what was an otherwise unexplained reference to a book about a supposed nuclear detonation in Thuringia. The book "Hitler's Bomb" has been cast into serious doubt by soil testing at the site that shows no evidence of contamination that would be associated with this supposed event. Honestly, however, this is such a red herring that perhaps the entire section should come out of the article. Ftjrwrites (talk) 16:56, 10 December 2007 (UTC)

1945
Thuringa was liberated from the US army and traded for West-Berlin. — Preceding unsigned comment added by Darktrym (talk • contribs) 19:08, 2 February 2011 (UTC)

former states
it would be interesting to know what former states were merged to make the free state. Tinynanorobots (talk) 16:34, 29 June 2011 (UTC)

don't get the positions in this table
5. 	Gotha 	       57.256 	48.376 	47.045 	Gotha 6. 	Eisenach 	50.059 	44.442 	37.858 	independent city 7. 	Nordhausen 	42.018 	45.633 	43.781 	Nordhausen

Why is Eisenach on place 6? Nordhausen and Gotha are both bigger! Now as well as in 2005 (last number-column). BTW: If it is an importance rating Eisenach needs to be higher than Gotha (Econ and Tourisim wise). — Preceding unsigned comment added by 134.28.70.76 (talk) 12:13, 19 September 2011 (UTC)

Move
This article should be moved to Free State of Thuringia -Ilhador- (talk) 00:20, 18 December 2011 (UTC)

potential resource
"Germany's regional disparities fuel neo-Nazi culture; During a train trip across Germany, a Monitor correspondent noted regional differences that make neo-Nazi culture appealing in the east and alien in the west. A murder last week exposed the existence neo-Nazi cells in the country." by Isabelle de Pommereau, Christian Science Monitor November 17, 2011, excerpt ... See de:Rock für Deutschland 99.181.153.29 (talk) 06:12, 29 December 2011 (UTC)

District map
The numbers on the district map don't correspond to the numbers in the table of districts. Also, the map itself is outdated and should be superseded by File:Thüringen Kreise (nummeriert).svg. Unless there are objections I'll modify the table numbers to correspond to the map. Huon (talk) 21:19, 13 August 2013 (UTC)
 * Go ahead and change that. I was hopelessly confused in trying to look up districts on the west side of the district, as the map is currently useless for that. Nerfer (talk) 20:38, 15 October 2013 (UTC)

Did Goethe work at the University of Jena?
The introduction claims that Goethe worked at the Unversity of Jena. Are there any sources supporting this? I know he is responsible for some changes at the university (he's supposed to have suggested the creation of the botanical garden), but I thought that this was in his role as minister for education, and not as an academic or administrator at the university. GroupCohomologist (talk) 20:36, 18 September 2014 (UTC)

Is Karl Marx' connection to Thuringia significant?
This article recently acquired a list of notable persons with significant links to Thuringia. In particular, Karl Marx is listed, as he received his Ph.D. from the University of Jena. At first sight this means he should obviously be on the list, but a closer inspection of the facts gives a different impression. According to the article on Marx, he did all his thesis work in Berlin but was concerned that the conservative Berlin faculty would reject his thesis for political reasons: so he submitted it to the more liberal university in Jena instead, and took the degree in absentia. This was his only link to Thuringia. To me it is so tenuous that he should be removed from the list.

Caveat: This is a politically sensitive issue, and related to the question of whether the Friedrich-Schiller-Universität should display the Marx bust which featured so prominently in GDR days. Some people might feel that my suggestion reeks of triumphalism over the fall of the GDR; and in the light of current political developments in Thuringia it will be interesting to see what happens to the Marx bust in the future. GroupCohomologist (talk) 21:25, 27 October 2014 (UTC)

External links modified
Hello fellow Wikipedians,

I have just added archive links to 1 one external link on Thuringia. Please take a moment to review my edit. If necessary, add after the link to keep me from modifying it. Alternatively, you can add to keep me off the page altogether. I made the following changes:
 * Added archive http://web.archive.org/web/20110916231247/http://www.leg-thueringen.de/index.php?id=1982&L=1 to http://www.leg-thueringen.de/index.php?id=1982&L=1

When you have finished reviewing my changes, please set the checked parameter below to true to let others know.

Cheers.—cyberbot II  Talk to my owner :Online 15:00, 27 February 2016 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified 2 external links on Thuringia. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added archive https://web.archive.org/web/20160304052707/https://www.helaba.de/en/DieHelaba/MaerkteUndAnalysen/ResearchUndVolkswirtschaft/Bundeslaender/Downloads/20140402-ZahlenundFakten.pdf to https://www.helaba.de/en/DieHelaba/MaerkteUndAnalysen/ResearchUndVolkswirtschaft/Bundeslaender/Downloads/20140402-ZahlenundFakten.pdf
 * Added archive https://web.archive.org/web/20160304052707/https://www.helaba.de/en/DieHelaba/MaerkteUndAnalysen/ResearchUndVolkswirtschaft/Bundeslaender/Downloads/20140402-ZahlenundFakten.pdf to https://www.helaba.de/en/DieHelaba/MaerkteUndAnalysen/ResearchUndVolkswirtschaft/Bundeslaender/Downloads/20140402-ZahlenundFakten.pdf

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 19:42, 26 July 2017 (UTC)

A Commons file used on this page or its Wikidata item has been nominated for deletion
The following Wikimedia Commons file used on this page or its Wikidata item has been nominated for deletion: Participate in the deletion discussion at the. —Community Tech bot (talk) 04:54, 6 January 2022 (UTC)
 * Friedrich Schiller by Ludovike Simanowiz.jpg

title: Talk:Thuringia


text:
Mickey Finn (drugs)

In slang, a Mickey Finn (or simply a Mickey) is a drink laced with an incapacitating agent, particularly chloral hydrate, given to someone without their knowledge with the intent to incapacitate them or "knock them out"; hence the colloquial name knockout drops. Serving someone a "Mickey" is most commonly referred to as "slipping someone a mickey".

The "spiking" of drinks is a practice used by sexual predators at drinking establishments who lace alcoholic drinks with sedative drugs.

Michael "Mickey" Finn
The "Mickey Finn" is most likely named after the manager and bartender of the Lone Star Saloon and Palm Garden Restaurant, which operated on South State Street in the Loop neighborhood of Chicago from 1896 to 1903. In December 1903, several Chicago newspapers documented that a Michael "Mickey" Finn managed the Lone Star Saloon and was accused of using knockout drops to incapacitate and rob some of his customers. Moreover, the first known written example of the term, according to the Oxford English Dictionary (OED), is in 1915, 12 years after his trial.

The first popular account of Mickey Finn was given by Herbert Asbury in his 1940 book Gem of the Prairie: An Informal History of the Chicago Underworld. His cited sources are Chicago newspapers and the 1903 court testimony of Lone Star prostitute "Gold Tooth" Mary Thornton. Before his days as a saloon proprietor, Mickey Finn was known as a pickpocket and thief who often preyed on drunken bar patrons. The act of serving a Mickey Finn Special was a coordinated robbery orchestrated by Finn. First, Finn or one of his employees (including "house girls") would slip chloral hydrate into the unsuspecting patron's drink. The incapacitated patron would be escorted or carried into a back room by one of Finn's associates, who would then rob him and dump him in an alley. The victim would wake up the next morning in a nearby alley and would remember little or nothing of what had happened.

Finn's saloon was ordered to be closed on December 16, 1903. He was apparently arrested again in 1918, this time for running an illegal bar in South Chicago.

Chicago restaurant poisonings
On June 22, 1918, four people were arrested and over one hundred waiters taken into custody over the apparent widespread practice of poisoning by waiters in Chicago. Guests who tipped poorly were given "Mickey Finn powder" in their food or drinks. Chemical analysis showed that it contained antimony potassium tartrate, also called "emetic tartar"; which in addition to causing vomiting, headaches, dizziness and depression, can be lethal in large quantities. Two bartenders were arrested for selling the powder at the bar at the waiters' union headquarters, and W. Stuart Wood and his wife were arrested for manufacturing the powder. Wood sold packets of it for 20 cents and referred to it as "Mickey Finn Powder" in a letter to union bartender John Millian. A follow-up article mentions the pursuit of a man named Jean Crones, who was believed to be responsible for poisoning over 100 people at a Chicago University Club banquet at which three people died.

Media
The OED gives a chronology of the term, starting in 1915:
 * The 1915 citation is from a photograph of a saloon in the December 26 edition of the Los Angeles Examiner. In the photograph is a sign that reads: "Try a Michael Finn cocktail".
 * The first listed reference as a knock-out drop in the OED: "Wish I had a drink and a Mike Finn for him", is from a March 11, 1924 article in the New York Evening Journal.
 * A description of a Mickey Finn is given in the January 18, 1927 issue of the Bismarck Tribune: "A Mickey Finn is an up-to-date variant on the knock-out drops of pre-war days."
 * In the September 3, 1927 issue of the Chicago Daily Tribune, the phrase appears in an article on the use of ethylene for artificial ripening of fruit: "Applied to a human, ethylene is an anaesthetic as the old-time Mickey Finn in a lumber-jack saloon."
 * In John O'Hara's 1934 novel Appointment in Samarra, a disgruntled headwaiter remarks of a poor tipper, "I'd like to give him a Mickey Finn."
 * In the 1940 film The Bank Dick, W.C. Fields' character Egbert Sousé tries to put the virtuous bank examiner J. Pinkerton Snoopington (Franklin Pangborn) out of action by buying him a drink at a bar. Egbert says to the bartender, "Has, uh, Michael Finn been in here today?" To which the bartender replies, "No, but he will be."
 * In the animated Superman movie Showdown (1942), a gangster (who dresses like Superman to rob people and businesses) pockets $5 from his take. The mob boss sees this, hits him and takes it. The Superman impersonator says, "Gee boss, it was only a fin." The mob boss replies, "Next time it will be a Mickey Finn."
 * In the 1946 film Three Little Pirates, starring slapstick comedy group The Three Stooges, Moe offers to give a castle guard a Mickey Finn.
 * In the 1946 Looney Tunes short film Hare Remover, after Elmer Fudd traps Bugs Bunny, he tries to give Bugs his potion, to which Bugs says to the audience, "This guy's trying to slip me a Mickey."
 * In the 1957 black comedy movie The Naked Truth, Peggy Mount plays a character who is one of several victims of blackmail by Dennis Price. Her plot line consists of her attempts to obtain a Mickey Finn to incapacitate the villain, before murdering him. She subsequently uses one on Terry-Thomas, a fellow victim she mistakes for the blackmailer.
 * In the 1957 novel A Rage in Harlem, Jackson's crossdressing brother gives him "a Mickey Finn".
 * In an episode of I Love Lucy, Fred recommends Ricky "slip [Lucy] a Mickey" as he does to Ethel when she's bothering him. (However, Fred says it is not actually a Mickey.)
 * In David Niven's book Bring on the Empty Horses (1975), he writes of Clark Gable's gate man slipping "an old-fashioned Mickey Finn" into his drink and driving him home "semi-conscious".
 * In the 1976 Columbo episode "A Matter of Honor" (episode 35), on examining a drugs cabinet, Columbo says, "Chloral hydrate? I'll tell you I don't know much about drugs but that's the stuff they put in a Mickey Finn. That's an American expression; knockout drops." (end of the 56th minute)
 * In the 1977 musical Annie, the term "Mickey Finn" is used in the song "It's the Hard Knock Life" by a group of orphaned children who fantasize about taking revenge on their abusive caretaker.
 * In the 1979 episode of Happy Days, "King Richard's Big Knight", a college bully, slips Richie a Mikey Finn, causing him to completely lose his inhibitions.
 * In the 1981 song "The Friends of Mr Cairo" on the album of the same name, the lyric runs: "That night, the double crosser got it right / Pretending he was really dim / He slipped to Sam a double gin (Mickey Finn) / He woke, the boys had gone, but not his gun / They'd left a note to lead him on / The chase to find the Maltese Falcon."
 * In the seventh episode of the second season of Seinfeld, "The Revenge" (1991), George Costanza tries to 'slip a Mickey' in the drink of his former boss.
 * On the original airing (January 23, 1993, Season 5, Episode 15) of Empty Nest, "The Fracas in Vegas", Harry and Charlie, while on a Las Vegas trip, were conned by two women who slipped them "Mickeys" to steal all their belongings.
 * In Erykah Badu's song "Certainly" from the 1997 album Baduizm, she sings "You tried to get a little tricky, turned my back and then you slipped me a mickey."
 * In the 2008 song "Royal Flush" by Australian Hip-hop trio Bliss n Eso, Eso raps, "...Like a boring board meeting and I slip myself a mickey."
 * In the 2008 song "The Fix" by English alternative rock band Elbow, Guy Garvey sings "we've loaded the saddles, the mickeys are slipped".
 * In the 2011 video game L.A. Noire, a character in the game uses the name Micky Finn to describe what someone slipped them in their cocktails.
 * In a 2013 episode of The Big Bang Theory, "The Raiders Minimization", during an unexpected video chat by Sheldon, Amy recalls how a lone curly fry in Sheldon's regular fries led him to believe someone was trying to "slip [him] a Mickie."
 * In the 2020 David Fincher movie Mank, Herman Mankiewicz (Gary Oldman) is drugged by drinking a bottle sent by Orson Welles (Tom Burke). He says, "You sly thing, you slipped me a Mickey."

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Mickey Finn (drugs)


text:
Talk:Loyalist feud

Confusing
Erm...this needs work. Dates? A little context? Is this title a little too vague? --The Cunctator

 * Yes. Please explain what "C Company" is, and other background for those who do not know much about the subject but wish to learn. -- Infrogmation 06:01 Feb 15, 2003 (UTC)

Don't worry if you don't understand it. 99% of Irish people (north and south) can't make head or tail of this loyalist feud either. In fact a lot can't make head or tail of Northern Ireland!!! JTD 06:17 Feb 15, 2003 (UTC)

Before it starts, this article really needs to define 'loyalist' and where they fit in on the confusing mess that is NI politics. JTD 04:13 Feb 22, 2003 (UTC)

 * Is Red Hand Commanders really the right name? There are precious few Google hits for this. Isn't it Red Hand Defenders? Evercat 18:30, 3 Sep 2003 (UTC)

I have heard both. Certainly 90% of the time the latter but the former is also used. Whether it is a misname or a break-away of a break-away God only knows. FearÉIREANN 19:34, 3 Sep 2003 (UTC)

No it's Red Hand Commandos and it's a different group to Red Hand Defenders Dermo69

UVF and LVF
There needs to be some information on the founding of the LVF by Billy Wright after the Mid-Ulster UVF was stood down by the UVF's Brigade Staff.--Jeanne Boleyn (talk) 07:54, 8 June 2011 (UTC)

Waller and Shaw killings
These need to be fleshed out as Martin Dillon alleged that Lenny Murphy carried out the shooting of Noel Shaw.--Jeanne Boleyn (talk) 08:44, 14 December 2011 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified 2 external links on Loyalist feud. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added archive https://web.archive.org/web/20110721133809/http://www.tribune.ie/news/article/2008/nov/23/building-bridges-with-the-uda/ to http://www.tribune.ie/news/article/2008/nov/23/building-bridges-with-the-uda
 * Added archive https://web.archive.org/web/20021215231748/http://www.terrorismanswers.com/groups/uvf.html to http://www.terrorismanswers.com/groups/uvf.html

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 01:43, 7 December 2017 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified one external link on Loyalist feud. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added archive https://web.archive.org/web/20160927202802/http://www.sundayworld.com/news/northern-ireland/udas-big-bill-does-a-runner-as-feud-looms-spain-uda-tigers-bay to http://www.sundayworld.com/news/northern-ireland/udas-big-bill-does-a-runner-as-feud-looms-spain-uda-tigers-bay

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 18:37, 7 January 2018 (UTC)

False addition removed again
Links to other Wikipedia articles are not sources, and UCDP source nothing at all. They source 100 deaths for the UDA, but say nothing about whether those deaths were part of a loyalist feud. Looking at the graph they list 6 deaths for 1989, 6 for 1990, 12 for 1991, 22 for 1993, 32 for 1993, 10 for 1994, 2 for 1997, 2 for 1998, 1 for 2000, 1 for 2001, 3 for 2002, 1 for 2003, 1 for 2004 and 1 for 2005. That does indeed total 100. But anyone with even a basic knowledge of the Troubles will tell you that the idea that the UDA killed 32 people as part of a loyalist feud in 1993 is simply wrong in every way possible. Those deaths are all the people killed by the UDA in those years, not ones killed as part of a loyalist feud. Kathleen's bike (talk) 14:00, 12 April 2023 (UTC)

 * Civilian casualties are linked into the feud 'cause those killings happen during feuds periods. Those killings are linked into the violence, so pls stop remove Kvaratskhelia77 (talk) 16:57, 12 April 2023 (UTC)
 * Indeed I also don't considered the killings before 1998 made by UDA, I inserect only the killings from 1998 (end of the conflict), so anyone with a basic knowledge of a conflict situation can tell you that those killings are linked into the feuds, indeed if you check on the actions made up by paramilitaries groups every protestant civilians killings are linked into the feuds. Kvaratskhelia77 (talk) 17:03, 12 April 2023 (UTC)

 * You do not have a clue about this subject, or any other relating to Ireland. You are not improving the encyclopedia, you are damaging it by the addition of false information. Should you create yet another sock, I recommend not editing Ireland related articles again. Kathleen's bike (talk) 17:26, 12 April 2023 (UTC)

title: Talk:Loyalist feud


text:
User talk:Adrian Kirkup

Adrian To reply to this message edit this page.Theresa knott
 * I've just replied to my own message to you.Theresa knott

Hi Theresa. Thanks for the email. I notice my other problem has sorted out- by itself?
 * I still don't know what your other problem was, and I can't check my email 'till tomorrow.

Time for some more play. - if you change a link on a page from how to make a % solution to how to make a % solution you lose the link to the page 'how to make a % solution. Which is why I've changed it back. If you don't like the title of a page you should move the page [click the 'move this page' link on the page you wan't to move. This will redirect all links to the old page to your new page and it copies the text and history of the old page to the new one. Then you can go back and change the links. {I hope this makes sense. I'm pretty tired as I write this Theresa knott

Clear as mud. I noticed some of your links had capital letters eg Potassium Iodide which seems to be a no-no (you get there but also get a note at the top that says "redirected from Potassium Iodide") I think the problem I had was that I was checking the page too soon- hadn't locked into the Web or summat. I notice too that if you make a link with a |sign, the only thing that appears is whatever is written after the |. Sometimes that doesn't make grammatic sense, so I switched some around. Maybe that alters the links? Adrian

title: User talk:Adrian Kirkup


text:
Mach's principle

In theoretical physics, particularly in discussions of gravitation theories, Mach's principle (or Mach's conjecture ) is the name given by Albert Einstein to an imprecise hypothesis often credited to the physicist and philosopher Ernst Mach. The hypothesis attempted to explain how rotating objects, such as gyroscopes and spinning celestial bodies, maintain a frame of reference.

The proposition is that the existence of absolute rotation (the distinction of local inertial frames vs. rotating reference frames) is determined by the large-scale distribution of matter, as exemplified by this anecdote: You are standing in a field looking at the stars. Your arms are resting freely at your side, and you see that the distant stars are not moving. Now start spinning. The stars are whirling around you and your arms are pulled away from your body. Why should your arms be pulled away when the stars are whirling? Why should they be dangling freely when the stars don't move?

Mach's principle says that this is not a coincidence—that there is a physical law that relates the motion of the distant stars to the local inertial frame. If you see all the stars whirling around you, Mach suggests that there is some physical law which would make it so you would feel a centrifugal force. There are a number of rival formulations of the principle, often stated in vague ways like "mass out there influences inertia here". A very general statement of Mach's principle is "local physical laws are determined by the large-scale structure of the universe".

Mach's concept was a guiding factor in Einstein's development of the general theory of relativity. Einstein realized that the overall distribution of matter would determine the metric tensor which indicates which frame is stationary with respect to rotation. Frame-dragging and conservation of gravitational angular momentum makes this into a true statement in the general theory in certain solutions. But because the principle is so vague, many distinct statements have been made which would qualify as a Mach principle, some of which are false. The Gödel rotating universe is a solution of the field equations that is designed to disobey Mach's principle in the worst possible way. In this example, the distant stars seem to be revolving faster and faster as one moves further away. This example does not completely settle the question of the physical relevance of the principle because it has closed timelike curves.

History
Mach put forth the idea in his book The Science of Mechanics (1883 in German, 1893 in English). Before Mach's time, the basic idea also appears in the writings of George Berkeley. After Mach, the book Absolute or Relative Motion? (1896) by Benedict Friedlaender and his brother Immanuel contained ideas similar to Mach's principle.

Einstein's use of the principle
There is a fundamental issue in relativity theory: if all motion is relative, how can we measure the inertia of a body? We must measure the inertia with respect to something else. But what if we imagine a particle completely on its own in the universe? We might hope to still have some notion of its state of motion. Mach's principle is sometimes interpreted as the statement that such a particle's state of motion has no meaning in that case.

In Mach's words, the principle is embodied as follows:

"[The] investigator must feel the need of... knowledge of the immediate connections, say, of the masses of the universe. There will hover before him as an ideal insight into the principles of the whole matter, from which accelerated and inertial motions will result in the same way."

Albert Einstein seemed to view Mach's principle as something along the lines of:

"...inertia originates in a kind of interaction between bodies..."

In this sense, at least some of Mach's principles are related to philosophical holism. Mach's suggestion can be taken as the injunction that gravitation theories should be relational theories. Einstein brought the principle into mainstream physics while working on general relativity. Indeed, it was Einstein who first coined the phrase Mach's principle. There is much debate as to whether Mach really intended to suggest a new physical law since he never states it explicitly.

The writing in which Einstein found inspiration was Mach's book The Science of Mechanics (1883, tr. 1893), where the philosopher criticized Newton's idea of absolute space, in particular the argument that Newton gave sustaining the existence of an advantaged reference system: what is commonly called "Newton's bucket argument".

In his Philosophiae Naturalis Principia Mathematica, Newton tried to demonstrate that one can always decide if one is rotating with respect to the absolute space, measuring the apparent forces that arise only when an absolute rotation is performed. If a bucket is filled with water, and made to rotate, initially the water remains still, but then, gradually, the walls of the vessel communicate their motion to the water, making it curve and climb up the borders of the bucket, because of the centrifugal forces produced by the rotation. This experiment demonstrates that the centrifugal forces arise only when the water is in rotation with respect to the absolute space (represented here by the earth's reference frame, or better, the distant stars) instead, when the bucket was rotating with respect to the water no centrifugal forces were produced, this indicating that the latter was still with respect to the absolute space.

Mach, in his book, says that the bucket experiment only demonstrates that when the water is in rotation with respect to the bucket no centrifugal forces are produced, and that we cannot know how the water would behave if in the experiment the bucket's walls were increased in depth and width until they became leagues big. In Mach's idea this concept of absolute motion should be substituted with a total relativism in which every motion, uniform or accelerated, has sense only in reference to other bodies (i.e., one cannot simply say that the water is rotating, but must specify if it's rotating with respect to the vessel or to the earth). In this view, the apparent forces that seem to permit discrimination between relative and "absolute" motions should only be considered as an effect of the particular asymmetry that there is in our reference system between the bodies which we consider in motion, that are small (like buckets), and the bodies that we believe are still (the earth and distant stars), that are overwhelmingly bigger and heavier than the former.

This same thought had been expressed by the philosopher George Berkeley in his De Motu. It is then not clear, in the passages from Mach just mentioned, if the philosopher intended to formulate a new kind of physical action between heavy bodies. This physical mechanism should determine the inertia of bodies, in a way that the heavy and distant bodies of our universe should contribute the most to the inertial forces. More likely, Mach only suggested a mere "redescription of motion in space as experiences that do not invoke the term space". What is certain is that Einstein interpreted Mach's passage in the former way, originating a long-lasting debate.

Most physicists believe Mach's principle was never developed into a quantitative physical theory that would explain a mechanism by which the stars can have such an effect. Mach himself never made his principle exactly clear. Although Einstein was intrigued and inspired by Mach's principle, Einstein's formulation of the principle is not a fundamental assumption of general relativity, although the principle of equivalence of gravitational and inertial mass is most certainly fundamental.

Mach's principle in general relativity
Because intuitive notions of distance and time no longer apply, what exactly is meant by "Mach's principle" in general relativity is even less clear than in Newtonian physics and at least 21 formulations of Mach's principle are possible, some being considered more strongly Machian than others. A relatively weak formulation is the assertion that the motion of matter in one place should affect which frames are inertial in another.

Einstein, before completing his development of the general theory of relativity, found an effect which he interpreted as being evidence of Mach's principle. We assume a fixed background for conceptual simplicity, construct a large spherical shell of mass, and set it spinning in that background. The reference frame in the interior of this shell will precess with respect to the fixed background. This effect is known as the Lense–Thirring effect. Einstein was so satisfied with this manifestation of Mach's principle that he wrote a letter to Mach expressing this: "it... turns out that inertia originates in a kind of interaction between bodies, quite in the sense of your considerations on Newton's pail experiment... If one rotates [a heavy shell of matter] relative to the fixed stars about an axis going through its center, a Coriolis force arises in the interior of the shell; that is, the plane of a Foucault pendulum is dragged around (with a practically unmeasurably small angular velocity)."

The Lense–Thirring effect certainly satisfies the very basic and broad notion that "matter there influences inertia here". The plane of the pendulum would not be dragged around if the shell of matter were not present, or if it were not spinning. As for the statement that "inertia originates in a kind of interaction between bodies", this, too, could be interpreted as true in the context of the effect.

More fundamental to the problem, however, is the very existence of a fixed background, which Einstein describes as "the fixed stars". Modern relativists see the imprints of Mach's principle in the initial-value problem. Essentially, we humans seem to wish to separate spacetime into slices of constant time. When we do this, Einstein's equations can be decomposed into one set of equations, which must be satisfied on each slice, and another set, which describe how to move between slices. The equations for an individual slice are elliptic partial differential equations. In general, this means that only part of the geometry of the slice can be given by the scientist, while the geometry everywhere else will then be dictated by Einstein's equations on the slice.

In the context of an asymptotically flat spacetime, the boundary conditions are given at infinity. Heuristically, the boundary conditions for an asymptotically flat universe define a frame with respect to which inertia has meaning. By performing a Lorentz transformation on the distant universe, of course, this inertia can also be transformed.

A stronger form of Mach's principle applies in Wheeler–Mach–Einstein spacetimes, which require spacetime to be spatially compact and globally hyperbolic. In such universes Mach's principle can be stated as the distribution of matter and field energy-momentum (and possibly other information) at a particular moment in the universe determines the inertial frame at each point in the universe (where "a particular moment in the universe" refers to a chosen Cauchy surface).

There have been other attempts to formulate a theory that is more fully Machian, such as the Brans–Dicke theory and the Hoyle–Narlikar theory of gravity, but most physicists argue that none have been fully successful. At an exit poll of experts, held in Tübingen in 1993, when asked the question "Is general relativity perfectly Machian?", 3 respondents replied "yes", and 22 replied "no". To the question "Is general relativity with appropriate boundary conditions of closure of some kind very Machian?" the result was 14 "yes" and 7 "no".

However, Einstein was convinced that a valid theory of gravity would necessarily have to include the relativity of inertia: "So strongly did Einstein believe at that time in the relativity of inertia that in 1918 he stated as being on an equal footing three principles on which a satisfactory theory of gravitation should rest: In 1922, Einstein noted that others were satisfied to proceed without this [third] criterion and added, "This contentedness will appear incomprehensible to a later generation however."
 * 1) The principle of relativity as expressed by general covariance.
 * 2) The principle of equivalence.
 * 3) Mach's principle (the first time this term entered the literature): … that the gµν are completely determined by the mass of bodies, more generally by Tµν.

It must be said that, as far as I can see, to this day, Mach's principle has not brought physics decisively farther. It must also be said that the origin of inertia is and remains the most obscure subject in the theory of particles and fields. Mach's principle may therefore have a future – but not without the quantum theory."

- Abraham Pais

Inertial induction
In 1953, in order to express Mach's Principle in quantitative terms, the Cambridge University physicist Dennis W. Sciama proposed the addition of an acceleration dependent term to the Newtonian gravitation equation. Sciama's acceleration dependent term was $F = G \frac{m_A m_B \bf a}{rc^2}\ $ where r is the distance between the particles, G is the gravitational constant, a is the relative acceleration and c represents the speed of light in vacuum. Sciama referred to the effect of the acceleration dependent term as Inertial Induction.

Variations in the statement of the principle
The broad notion that "mass there influences inertia here" has been expressed in several forms. Hermann Bondi and Joseph Samuel have listed eleven distinct statements that can be called Mach principles, labelled Mach0 through Mach10 (taking inspiration from the Mach number). Though their list is not necessarily exhaustive, it does give a flavor for the variety possible.

 * 1) The universe, as represented by the average motion of distant galaxies, does not appear to rotate relative to local inertial frames.
 * 2) Newton's gravitational constant G is a dynamical field.
 * 3) An isolated body in otherwise empty space has no inertia.
 * 4) Local inertial frames are affected by the cosmic motion and distribution of matter.
 * 5) The universe is spatially closed.
 * 6) The total energy, angular and linear momentum of the universe are zero.
 * 7) Inertial mass is affected by the global distribution of matter.
 * 8) If you take away all matter, there is no more space.
 * 9) $$\Omega\ \stackrel{\text{def}}{=}\ 4 \pi \rho G T^2$$ is a definite number, of order unity, where $$\rho$$ is the mean density of matter in the universe, and $$T$$ is the Hubble time.
 * 10) The theory contains no absolute elements.
 * 11) Overall rigid rotations and translations of a system are unobservable.

title: Mach's principle


text:
De Havilland Comet

The de Havilland DH.106 Comet is the world's first commercial jet airliner. Developed and manufactured by de Havilland in the United Kingdom, the Comet 1 prototype first flew in 1949. It features an aerodynamically clean design with four de Havilland Ghost turbojet engines buried in the wing roots, a pressurised cabin, and large windows. For the era, it offered a relatively quiet, comfortable passenger cabin and was commercially promising at its debut in 1952.

Within a year of the airliner's entry into service, three Comets were lost in highly publicized accidents after suffering catastrophic mishaps mid-flight. Two of these were found to be caused by structural failure resulting from metal fatigue in the airframe, a phenomenon not fully understood at the time; the other was due to overstressing of the airframe during flight through severe weather. The Comet was withdrawn from service and extensively tested. Design and construction flaws, including improper riveting and dangerous stress concentrations around square cut-outs for the ADF (automatic direction finder) antennas were ultimately identified. As a result, the Comet was extensively redesigned, with structural reinforcements and other changes. Rival manufacturers heeded the lessons learned from the Comet when developing their own aircraft.

Although sales never fully recovered, the improved Comet 2 and the prototype Comet 3 culminated in the redesigned Comet 4 series which debuted in 1958 and remained in commercial service until 1981. The Comet was also adapted for a variety of military roles such as VIP, medical and passenger transport, as well as surveillance; the last Comet 4, used as a research platform, made its final flight in 1997. The most extensive modification resulted in a specialised maritime patrol derivative, the Hawker Siddeley Nimrod, which remained in service with the Royal Air Force until 2011, over 60 years after the Comet's first flight.

Origins

On 11 March 1943, the Cabinet of the United Kingdom formed the Brabazon Committee, which was tasked with determining the UK's airliner needs after the conclusion of the Second World War. One of its recommendations was for the development and production of a pressurised, transatlantic mailplane that could carry 1 LT of payload at a cruising speed of 400 mph non-stop. Aviation company de Havilland was interested in this requirement, but chose to challenge the then widely held view that jet engines were too fuel-hungry and unreliable for such a role. As a result, committee member Sir Geoffrey de Havilland, head of the de Havilland company, used his personal influence and his company's expertise to champion the development of a jet-propelled aircraft; proposing a specification for a pure turbojet-powered design.

The committee accepted the proposal, calling it the "Type IV" (of five designs), and in 1945 awarded a development and production contract to de Havilland under the designation Type 106. The type and design were to be so advanced that de Havilland had to undertake the design and development of both the airframe and the engines. This was because in 1945 no turbojet engine manufacturer in the world was drawing-up a design specification for an engine with the thrust and specific fuel consumption that could power an aircraft at the proposed cruising altitude (40000 ft), speed, and transatlantic range as was called for by the Type 106. First-phase development of the DH.106 focused on short- and intermediate-range mailplanes with small passenger compartments and as few as six seats, before being redefined as a long-range airliner with a capacity of 24 seats. Out of all the Brabazon designs, the DH.106 was seen as the riskiest: both in terms of introducing untried design elements and for the financial commitment involved. Nevertheless, the British Overseas Airways Corporation (BOAC) found the Type IV's specifications attractive, and initially proposed a purchase of 25 aircraft; in December 1945, when a firm contract was created, the order total was revised to 10.

A design team was formed in 1946 under the leadership of chief designer Ronald Bishop, who had been responsible for the Mosquito fighter-bomber. Several unorthodox configurations were considered, ranging from canard to tailless designs; All were rejected. The Ministry of Supply was interested in the most radical of the proposed designs, and ordered two experimental tailless DH 108s to serve as proof of concept aircraft for testing swept-wing configurations in both low-speed and high-speed flight. During flight tests, the DH 108 gained a reputation for being accident-prone and unstable, leading de Havilland and BOAC to gravitate to conventional configurations and, necessarily, designs with less technical risk. The DH 108s were later modified to test the DH.106's power controls.

In September 1946, before completion of the DH 108s, BOAC requests necessitated a redesign of the DH.106 from its previous 24-seat configuration to a larger 36-seat version. With no time to develop the technology necessary for a proposed tailless configuration, Bishop opted for a more conventional 20-degree swept-wing design with unswept tail surfaces, married to an enlarged fuselage accommodating 36 passengers in a four-abreast arrangement with a central aisle. Replacing previously specified Halford H.1 Goblin engines, four new, more-powerful Rolls-Royce Avons were to be incorporated in pairs buried in the wing roots; Halford H.2 Ghost engines were eventually applied as an interim solution while the Avons cleared certification. The redesigned aircraft was named the DH.106 Comet in December 1947. Revised first orders from BOAC and British South American Airways totalled 14 aircraft, with delivery projected for 1952.

Testing and prototypes
As the Comet represented a new category of passenger aircraft, more rigorous testing was a development priority. From 1947 to 1948, de Havilland conducted an extensive research and development phase, including the use of several stress test rigs at Hatfield Aerodrome for small components and large assemblies alike. Sections of pressurised fuselage were subjected to high-altitude flight conditions via a large decompression chamber on-site and tested to failure. Tracing fuselage failure points proved difficult with this method, and de Havilland ultimately switched to conducting structural tests with a water tank that could be safely configured to increase pressures gradually. The entire forward fuselage section was tested for metal fatigue by repeatedly pressurising to 2.75 psi overpressure and depressurising through more than 16,000 cycles, equivalent to about 40,000 hours of airline service. The windows were also tested under a pressure of 12 psi, 4.75 psi above expected pressures at the normal service ceiling of 36000 ft. One window frame survived 100 psi, about 1,250 per cent over the maximum pressure it was expected to encounter in service.

The first prototype DH.106 Comet (carrying Class B markings G-5-1) was completed in 1949 and was initially used to conduct ground tests and brief early flights. The prototype's maiden flight, out of Hatfield Aerodrome, took place on 27 July 1949 and lasted 31 minutes. At the controls was de Havilland chief test pilot John "Cats Eyes" Cunningham, a famous night-fighter pilot of the Second World War, along with co-pilot Harold "Tubby" Waters, engineers John Wilson (electrics) and Frank Reynolds (hydraulics), and flight test observer Tony Fairbrother.

The prototype was registered G-ALVG just before it was publicly displayed at the 1949 Farnborough Airshow before the start of flight trials. A year later, the second prototype G-5-2 made its maiden flight. The second prototype was registered G-ALZK in July 1950 and it was used by the BOAC Comet Unit at Hurn from April 1951 to carry out 500 flying hours of crew training and route-proving. Australian airline Qantas also sent its own technical experts to observe the performance of the prototypes, seeking to quell internal uncertainty about its prospective Comet purchase. Both prototypes could be externally distinguished from later Comets by the large single-wheeled main landing gear, which was replaced on production models starting with G-ALYP by four-wheeled bogies.

Overview
The Comet was an all-metal low-wing cantilever monoplane powered by four jet engines; it had a four-place cockpit occupied by two pilots, a flight engineer, and a navigator. The clean, low-drag design of the aircraft featured many design elements that were fairly uncommon at the time, including a swept-wing leading edge, integral wing fuel tanks, and four-wheel bogie main undercarriage units designed by de Havilland. Two pairs of turbojet engines (on the Comet 1s, Halford H.2 Ghosts, subsequently known as de Havilland Ghost 50 Mk1s) were buried in the wings.

The original Comet was the approximate length of, but not as wide as, the later Boeing 737-100, and carried fewer people in a significantly more-spacious environment. BOAC installed 36 reclining "slumberseats" with 45 in centres on its first Comets, allowing for greater leg room in front and behind; Air France had 11 rows of seats with four seats to a row installed on its Comets. Large picture window views and table seating accommodations for a row of passengers afforded a feeling of comfort and luxury unusual for transportation of the period. Amenities included a galley that could serve hot and cold food and drinks, a bar, and separate men's and women's toilets. Provisions for emergency situations included several life rafts stored in the wings near the engines, and individual life vests were stowed under each seat.

One of the most striking aspects of Comet travel was the quiet, "vibration-free flying" as touted by BOAC. For passengers used to propeller-driven airliners, smooth and quiet jet flight was a novel experience.

Avionics and systems
For ease of training and fleet conversion, de Havilland designed the Comet's flight deck layout with a degree of similarity to the Lockheed Constellation, an aircraft that was popular at the time with key customers such as BOAC. The cockpit included full dual-controls for the captain and first officer, and a flight engineer controlled several key systems, including fuel, air conditioning and electrical systems. The navigator occupied a dedicated station, with a table across from the flight engineer.

Several of the Comet's avionics systems were new to civil aviation. One such feature was irreversible, powered flight controls, which increased the pilot's ease of control and the safety of the aircraft by preventing aerodynamic forces from changing the directed positions and placement of the aircraft's control surfaces. Many of the control surfaces, such as the elevators, were equipped with a complex gearing system as a safeguard against accidentally over-stressing the surfaces or airframe at higher speed ranges.

The Comet had a total of four hydraulic systems: two primaries, one secondary, and a final emergency system for basic functions such as lowering the undercarriage. The undercarriage could also be lowered by a combination of gravity and a hand-pump. Power was syphoned from all four engines for the hydraulics, cabin air conditioning, and the de-icing system; these systems had operational redundancy in that they could keep working even if only a single engine was active. The majority of hydraulic components were centred in a single avionics bay. A pressurised refuelling system, developed by Flight Refuelling Ltd, allowed the Comet's fuel tanks to be refuelled at a far greater rate than by other methods.

The cockpit was significantly altered for the Comet 4's introduction, on which an improved layout focusing on the onboard navigational suite was introduced. An EKCO E160 radar unit was installed in the Comet 4's nose cone, providing search functions as well as ground and cloud-mapping capabilities, and a radar interface was built into the Comet 4 cockpit along with redesigned instruments.

Sud-Est's design bureau, while working on the Sud Aviation Caravelle in 1953, licensed several design features from de Havilland, building on previous collaborations on earlier licensed designs, including the DH 100 Vampire; the nose and cockpit layout of the Comet 1 was grafted onto the Caravelle. In 1969, when the Comet 4's design was modified by Hawker Siddeley to become the basis for the Nimrod, the cockpit layout was completely redesigned and bore little resemblance to its predecessors except for the control yoke.

Fuselage
Diverse geographic destinations and cabin pressurisation alike on the Comet demanded the use of a high proportion of alloys, plastics, and other materials new to civil aviation across the aircraft to meet certification requirements. The Comet's high cabin pressure and high operating speeds were unprecedented in commercial aviation, making its fuselage design an experimental process. At its introduction, Comet airframes would be subjected to an intense, high-speed operating schedule which included simultaneous extreme heat from desert airfields and frosty cold from the kerosene-filled fuel tanks, still cold from cruising at high altitude.

The Comet's thin metal skin was composed of advanced new alloys and was both riveted and chemically bonded, which saved weight and reduced the risk of fatigue cracks spreading from the rivets. The chemical bonding process was accomplished using a new adhesive, Redux, which was liberally used in the construction of the wings and the fuselage of the Comet; it also had the advantage of simplifying the manufacturing process.

When several of the fuselage alloys were discovered to be vulnerable to weakening via metal fatigue, a detailed routine inspection process was introduced. As well as thorough visual inspections of the outer skin, mandatory structural sampling was routinely conducted by both civil and military Comet operators. The need to inspect areas not easily viewable by the naked eye led to the introduction of widespread radiography examination in aviation; this also had the advantage of detecting cracks and flaws too small to be seen otherwise.

Operationally, the design of the cargo holds led to considerable difficulty for the ground crew, especially baggage handlers at the airports. The cargo hold had its doors located directly underneath the aircraft, so each item of baggage or cargo had to be loaded vertically upward from the top of the baggage truck, then slid along the hold floor to be stacked inside. The individual pieces of luggage and cargo also had to be retrieved in a similarly slow manner at the arriving airport.

Propulsion
The Comet was powered by two pairs of turbojet engines buried in the wings close to the fuselage. Chief designer Bishop chose the Comet's embedded-engine configuration because it avoided the drag of podded engines and allowed for a smaller fin and rudder since the hazards of asymmetric thrust were reduced. The engines were outfitted with baffles to reduce noise emissions, and extensive soundproofing was also implemented to improve passenger conditions.

Placing the engines within the wings had the advantage of a reduction in the risk of foreign object damage, which could seriously damage jet engines. The low-mounted engines and good placement of service panels also made aircraft maintenance easier to perform. The Comet's buried-engine configuration increased its structural weight and complexity. Armour had to be placed around the engine cells to contain debris from any serious engine failures; also, placing the engines inside the wing required a more complicated wing structure.

The Comet 1 featured 5050 lbf de Havilland Ghost 50 Mk1 turbojet engines. Two hydrogen peroxide-powered de Havilland Sprite booster rockets were originally intended to be installed to boost takeoff under hot and high altitude conditions from airports such as Khartoum and Nairobi. These were tested on 30 flights, but the Ghosts alone were considered powerful enough and some airlines concluded that rocket motors were impractical. Sprite fittings were retained on production aircraft. Comet 1s subsequently received more powerful 5700 lbf Ghost DGT3 series engines.

From the Comet 2 onward, the Ghost engines were replaced by the newer and more powerful 7000 lbf Rolls-Royce Avon AJ.65 engines. To achieve optimum efficiency with the new powerplants, the air intakes were enlarged to increase mass air flow. Upgraded Avon engines were introduced on the Comet 3, and the Avon-powered Comet 4 was highly praised for its takeoff performance from high-altitude locations such as Mexico City where it was operated by Mexicana de Aviacion, a major scheduled passenger air carrier.

Introduction
The earliest production aircraft, registered G-ALYP ("Yoke Peter"), first flew on 9 January 1951 and was subsequently lent to BOAC for development flying by its Comet Unit. On 22 January 1952, the fifth production aircraft, registered G-ALYS, received the first Certificate of Airworthiness awarded to a Comet, six months ahead of schedule. On 2 May 1952, as part of BOAC's route-proving trials, G-ALYP took off on the world's first jetliner flight with fare-paying passengers and inaugurated scheduled service from London to Johannesburg. The final Comet from BOAC's initial order, registered G-ALYZ, began flying in September 1952 and carried cargo along South American routes while simulating passenger schedules.

Prince Philip returned from the Helsinki Olympic Games with G-ALYS on 4 August 1952. Queen Elizabeth, the Queen Mother and Princess Margaret were guests on a special flight of the Comet on 30 June 1953 hosted by Sir Geoffrey and Lady de Havilland. Flights on the Comet were about 50 per cent faster compared to advanced piston-engined aircraft such as the Douglas DC-6 (490 mph vs 315 mph, respectively), and a faster rate of climb further cut flight times. In August 1953 BOAC scheduled the nine-stop London to Tokyo flights by Comet for 36 hours, compared to 86 hours and 35 minutes on its Argonaut (a DC-4 variant) piston airliner. (Pan Am's DC-6B was scheduled for 46 hours 45 minutes.) The five-stop flight from London to Johannesburg was scheduled for 21 hr 20 min.

In their first year, Comets carried 30,000 passengers. As the aircraft could be profitable with a load factor as low as 43 per cent, commercial success was expected. The Ghost engines allowed the Comet to fly above weather that competitors had to fly through. They ran smoothly and were less noisy than piston engines, had low maintenance costs and were fuel-efficient above 30000 ft. In summer 1953, eight BOAC Comets left London each week: three to Johannesburg, two to Tokyo, two to Singapore and one to Colombo.

In 1953, the Comet appeared to have achieved success for de Havilland. Popular Mechanics wrote that Britain had a lead of three to five years on the rest of the world in jetliners. As well as the sales to BOAC, two French airlines, Union Aéromaritime de Transport and Air France, each acquired three Comet 1As, an upgraded variant with greater fuel capacity, for flights to West Africa and the Middle East. A slightly longer version of the Comet 1 with more powerful engines, the Comet 2, was being developed, and orders were placed by Air India, British Commonwealth Pacific Airlines, Japan Air Lines, Linea Aeropostal Venezolana, and Panair do Brasil. American carriers Capital Airlines, National Airlines and Pan Am placed orders for the planned Comet 3, an even-larger, longer-range version for transatlantic operations. Qantas was interested in the Comet 1 but concluded that a version with more range and better takeoff performance was needed for the London to Canberra route.

Early hull losses
On 26 October 1952, the Comet suffered its first hull loss when a BOAC flight departing Rome's Ciampino airport failed to become airborne and ran into rough ground at the end of the runway. Two passengers sustained minor injuries, but the aircraft, G-ALYZ, was a write-off. On 3 March 1953, a new Canadian Pacific Airlines Comet 1A, registered CF-CUN and named Empress of Hawaii, failed to become airborne while attempting a night takeoff from Karachi, Pakistan, on a delivery flight to Australia. The aircraft plunged into a dry drainage canal and collided with an embankment, killing all five crew and six passengers on board. The accident was the first fatal jetliner crash. In response, Canadian Pacific cancelled its remaining order for a second Comet 1A and never operated the type in commercial service.

Both early accidents were originally attributed to pilot error, as overrotation had led to a loss of lift from the leading edge of the aircraft's wings. It was later determined that the Comet's wing profile experienced a loss of lift at a high angle of attack, and its engine inlets also suffered a lack of pressure recovery in the same conditions. As a result, de Havilland re-profiled the wings' leading edge with a pronounced "droop", and wing fences were added to control spanwise flow. A fictionalised investigation into the Comet's takeoff accidents was the subject of the novel Cone of Silence (1959) by Arthur David Beaty, a former BOAC captain. Cone of Silence was made into a film in 1960, and Beaty also recounted the story of the Comet's takeoff accidents in a chapter of his non-fiction work, Strange Encounters: Mysteries of the Air (1984).

The Comet's second fatal accident occurred on 2 May 1953, when BOAC Flight 783, a Comet 1, registered G-ALYV, crashed in a severe thundersquall six minutes after taking off from Calcutta-Dum Dum (now Netaji Subhash Chandra Bose International Airport), India, killing all 43 on board. Witnesses observed the wingless Comet on fire plunging into the village of Jagalgori, leading investigators to suspect structural failure.

India Court of Inquiry
After the loss of G-ALYV, the Government of India convened a court of inquiry to examine the cause of the accident. Professor Natesan Srinivasan joined the inquiry as the main technical expert. A large portion of the aircraft was recovered and reassembled at Farnborough, during which the break-up was found to have begun with a left elevator spar failure in the horizontal stabilizer. The inquiry concluded that the aircraft had encountered extreme negative g-forces during takeoff; severe turbulence generated by adverse weather was determined to have induced down-loading, leading to the loss of the wings. Examination of the cockpit controls suggested that the pilot may have inadvertently over-stressed the aircraft when pulling out of a steep dive by over-manipulation of the fully powered flight controls. Investigators did not consider metal fatigue as a contributory cause.

The inquiry's recommendations revolved around the enforcement of stricter speed limits during turbulence, and two significant design changes also resulted: all Comets were equipped with weather radar and the "Q feel" system was introduced, which ensured that control column forces (invariably called stick forces) would be proportional to control loads. This artificial feel was the first of its kind to be introduced in any aircraft. The Comet 1 and 1A had been criticised for a lack of "feel" in their controls, and investigators suggested that this might have contributed to the pilot's alleged over-stressing of the aircraft; Comet chief test pilot John Cunningham contended that the jetliner flew smoothly and was highly responsive in a manner consistent with other de Havilland aircraft.

Comet disasters of 1954
Just over a year later, Rome's Ciampino airport, the site of the first Comet hull loss, was the origin of a more-disastrous Comet flight. On 10 January 1954, 20 minutes after taking off from Ciampino, the first production Comet, G-ALYP, broke up in mid-air while operating BOAC Flight 781 and crashed into the Mediterranean off the Italian island of Elba with the loss of all 35 on board. With no witnesses to the disaster and only partial radio transmissions as incomplete evidence, no obvious reason for the crash could be deduced. Engineers at de Havilland immediately recommended 60 modifications aimed at any possible design flaw, while the Abell Committee met to determine potential causes of the crash. BOAC also voluntarily grounded its Comet fleet pending investigation into the causes of the accident.

Abell Committee Court of Inquiry
Media attention centred on potential sabotage; other speculation ranged from clear-air turbulence to an explosion of vapour in an empty fuel tank. The Abell Committee focused on six potential aerodynamic and mechanical causes: control flutter (which had led to the loss of DH 108 prototypes), structural failure due to high loads or metal fatigue of the wing structure, failure of the powered flight controls, failure of the window panels leading to explosive decompression, or fire and other engine problems. The committee concluded that fire was the most likely cause of the problem, and changes were made to the aircraft to protect the engines and wings from damage that might lead to another fire.

During the investigation, the Royal Navy conducted recovery operations. The first pieces of wreckage were discovered on 12 February 1954 and the search continued until September 1954, by which time 70 per cent by weight of the main structure, 80 per cent of the power section, and 50 per cent of the aircraft's systems and equipment had been recovered. The forensic reconstruction effort had just begun when the Abell Committee reported its findings. No apparent fault in the aircraft was found, and the British government decided against opening a further public inquiry into the accident. The prestigious nature of the Comet project, particularly for the British aerospace industry, and the financial impact of the aircraft's grounding on BOAC's operations both served to pressure the inquiry to end without further investigation. Comet flights resumed on 23 March 1954.

On 8 April 1954, Comet G-ALYY ("Yoke Yoke"), on charter to South African Airways, was on a leg from Rome to Cairo (of a longer route, SA Flight 201 from London to Johannesburg), when it crashed in the Mediterranean near Naples with the loss of all 21 passengers and crew on board. The Comet fleet was immediately grounded once again and a large investigation board was formed under the direction of the Royal Aircraft Establishment (RAE). Prime Minister Winston Churchill tasked the Royal Navy with helping to locate and retrieve the wreckage so that the cause of the accident could be determined. The Comet's Certificate of Airworthiness was revoked, and Comet 1 line production was suspended at the Hatfield factory while the BOAC fleet was permanently grounded, cocooned and stored.

Cohen Committee Court of Inquiry

On 19 October 1954, the Cohen Committee was established to examine the causes of the Comet crashes. Chaired by Lord Cohen, the committee tasked an investigation team led by Sir Arnold Hall, Director of the RAE at Farnborough, to perform a more-detailed investigation. Hall's team began considering fatigue as the most likely cause of both accidents and initiated further research into measurable strain on the aircraft's skin. With the recovery of large sections of G-ALYP from the Elba crash and BOAC's donation of an identical airframe, G-ALYU, for further examination, an extensive "water torture" test eventually provided conclusive results. This time, the entire fuselage was tested in a dedicated water tank that was built specifically at Farnborough to accommodate its full length.

In water-tank testing, engineers subjected G-ALYU to repeated repressurisation and over-pressurisation, and on 24 June 1954, after 3,057 flight cycles (1,221 actual and 1,836 simulated), G-ALYU burst open. Hall, Geoffrey de Havilland and Bishop were immediately called to the scene, where the water tank was drained to reveal that the fuselage had ripped open at a bolt hole, forward of the forward left escape hatch cut out. The failure then occurred longitudinally along a fuselage stringer at the widest point of the fuselage and through a cut out for an escape hatch. The skin thickness was discovered to be insufficient to distribute the load across the structure, leading to overloading of fuselage frames adjacent to fuselage cut outs. (Cohen Inquiry accident report Fig 7). The fuselage frames did not have sufficient strength to prevent the crack from propagating. Although the fuselage failed after a number of cycles that represented three times the life of G-ALYP at the time of the accident, it was still much earlier than expected. A further test reproduced the same results. Based on these findings, Comet 1 structural failures could be expected at anywhere from 1,000 to 9,000 cycles. Before the Elba accident, G-ALYP had made 1,290 pressurised flights, while G-ALYY had made 900 pressurised flights before crashing. Dr P. B. Walker, Head of the Structures Department at the RAE, said he was not surprised by this, noting that the difference was about three to one, and previous experience with metal fatigue suggested a total range of nine to one between experiment and outcome in the field could result in failure.

The RAE also reconstructed about two-thirds of G-ALYP at Farnborough and found fatigue crack growth from a rivet hole at the low-drag fibreglass forward aperture around the Automatic Direction Finder, which had caused a catastrophic break-up of the aircraft in high-altitude flight. The exact origin of the fatigue failure could not be identified but was localised to the ADF antenna cut out. A countersunk bolt hole and manufacturing damage that had been repaired at the time of construction using methods that were common, but were likely insufficient allowing for the stresses involved, were both located along the failure crack. Once the crack initiated the skin failed from the point of the ADF cut out and propagated downward and rearward along a stringer resulting in an explosive decompression.

It was also found that the punch-rivet construction technique employed in the Comet's design had exacerbated its structural fatigue problems; the aircraft's windows had been engineered to be glued and riveted, but had been punch-riveted only. Unlike drill riveting, the imperfect nature of the hole created by punch-riveting could cause fatigue cracks to start developing around the rivet. Principal investigator Hall accepted the RAE's conclusion of design and construction flaws as the likely explanation for G-ALYU's structural failure after 3,060 pressurisation cycles.

Earlier structural indications
The issue of the lightness of Comet 1 construction (in order to not tax the relatively low thrust de Havilland Ghost engines), had been noted by de Havilland test pilot John Wilson, while flying the prototype during a Farnborough flypast in 1949. On the flight, he was accompanied by Chris Beaumont, Chief Test Pilot of the de Havilland Engine Company who stood in the entrance to the cockpit behind the Flight Engineer. He stated "Every time we pulled 2 1/2-3G to go around the corner, Chris found that the floor on which he was standing, bulging up and there was a loud bang at that speed from the nose of the aircraft where the skin 'panted' (flexed), so when we heard this bang we knew without checking the airspeed indicator, that we were doing 340 knots. In later years we realised that these were the indications of how flimsy the structure really was."

Square window myths

Despite findings of the Cohen Inquiry, a number of myths have evolved around the cause of the Comet 1's accidents. Most commonly quoted are the 'square' passenger windows. While the report noted that stress around fuselage cut-outs, emergency exits and windows was found to be much higher than expected due to DeHavilland's assumptions and testing methods the passenger windows shape has been commonly misunderstood and cited as a cause of the fuselage failure. In fact the mention of 'windows' in the Cohen report's conclusion, refers specifically to the origin point of failure in the ADF Antenna cut-out 'windows', located above the cockpit, not passenger windows. The shape of the passenger windows were not indicated in any failure mode detailed in the accident report and were not viewed as a contributing factor. A number of other pressurised airliners of the period including the Boeing 377 Stratocruiser, Douglas DC-7, and DC-8 had larger more 'square' windows than the Comet 1 and experienced no such failures. In fact, the Comet 1's window general shape resembles a slightly larger Boeing 737 window mounted horizontally. They are rectangular not square, have rounded corners and are within 5% of the radius of the Boeing 737 windows and virtually identical to modern airliners. Paul Withey, Professor of Casting at the University of Birmingham School of Metallurgy states in a video presentation delivered in 2019, analysing all available data that: "The fact that DeHavilland put oval windows into later marks, is not because of any 'squareness' of the windows that caused failure." "DeHavilland went to oval windows on the subsequent Marks because it was easier to Redux them in (use adhesive) – nothing to do with the stress concentration and it's purely to remove rivets." (from the structure)

Surviving Comet 1s can be seen on view at the RAF Museum Cosford and the DeHavilland Museum at Salisbury Hall, London Colney.

Response
In responding to the report de Havilland stated: "Now that the danger of high level fatigue in pressure cabins has been generally appreciated, de Havillands will take adequate measures to deal with this problem. To this end we propose to use thicker gauge materials in the pressure cabin area and to strengthen and redesign windows and cut outs and so lower the general stress to a level at which local stress concentrations either at rivets and bolt holes or as such may occur by reason of cracks caused accidentally during manufacture or subsequently, will not constitute a danger."

The Cohen inquiry closed on 24 November 1954, having "found that the basic design of the Comet was sound", and made no observations or recommendations regarding the shape of the windows. De Havilland nonetheless began a refit programme to strengthen the fuselage and wing structure, employing thicker-gauge skin and replacing the rectangular windows and panels with rounded versions, although this was not related to the erroneous 'square' window claim, as can be seen by the fact that the fuselage escape hatch cut-outs (the source of the failure in test aircraft G-ALYU) retained their rectangular shape.

Following the Comet enquiry, aircraft were designed to "fail-safe" or safe-life standards, though several subsequent catastrophic fatigue failures, such as Aloha Airlines Flight 243 of April 28, 1988 have occurred.

Resumption of service

With the discovery of the structural problems of the early series, all remaining Comets were withdrawn from service, while de Havilland launched a major effort to build a new version that would be both larger and stronger. All outstanding orders for the Comet 2 were cancelled by airline customers. All production Comet 2s were also modified with thicker gauge skin to better distribute loads and alleviate the fatigue problems (most of these served with the RAF as the Comet C2); a programme to produce a Comet 2 with more powerful Avons was delayed. The prototype Comet 3 first flew in July 1954 and was tested in an unpressurised state pending completion of the Cohen inquiry. Comet commercial flights would not resume until 1958.

Development flying and route proving with the Comet 3 allowed accelerated certification of what was destined to be the most successful variant of the type, the Comet 4. All airline customers for the Comet 3 subsequently cancelled their orders and switched to the Comet 4, which was based on the Comet 3 but with improved fuel capacity. BOAC ordered 19 Comet 4s in March 1955, and American operator Capital Airlines ordered 14 Comets in July 1956. Capital's order included 10 Comet 4As, a variant modified for short-range operations with a stretched fuselage and short wings, lacking the pinion (outboard wing) fuel tanks of the Comet 4. Financial problems and a takeover by United Airlines meant that Capital would never operate the Comet.

The Comet 4 first flew on 27 April 1958 and received its Certificate of Airworthiness on 24 September 1958; the first was delivered to BOAC the next day. The base price of a new Comet 4 was roughly £1.14 million (£ million in ). The Comet 4 enabled BOAC to inaugurate the first regular jet-powered transatlantic services on 4 October 1958 between London and New York (albeit still requiring a fuel stop at Gander International Airport, Newfoundland, on westward North Atlantic crossings). While BOAC gained publicity as the first to provide transatlantic jet service, by the end of the month rival Pan American World Airways was flying the Boeing 707 on the New York-Paris route, with a fuel stop at Gander in both directions, and in 1960 began flying Douglas DC-8's on its transatlantic routes as well. The American jets were larger, faster, longer-ranged and more cost-effective than the Comet. After analysing route structures for the Comet, BOAC reluctantly cast-about for a successor, and in 1956 entered into an agreement with Boeing to purchase the 707.

The Comet 4 was ordered by two other airlines: Aerolíneas Argentinas took delivery of six Comet 4s from 1959 to 1960, using them between Buenos Aires and Santiago, New York and Europe, and East African Airways received three new Comet 4s from 1960 to 1962 and operated them to the United Kingdom and to Kenya, Tanzania, and Uganda. The Comet 4A ordered by Capital Airlines was instead built for BEA as the Comet 4B, with a further fuselage stretch of 38 in and seating for 99 passengers. The first Comet 4B flew on 27 June 1959 and BEA began Tel Aviv to London-Heathrow services on 1 April 1960. Olympic Airways was the only other customer to order the type. The last Comet 4 variant, the Comet 4C, first flew on 31 October 1959 and entered service with Mexicana in 1960. The Comet 4C had the Comet 4B's longer fuselage and the longer wings and extra fuel tanks of the original Comet 4, which gave it a longer range than the 4B. Ordered by Kuwait Airways, Middle East Airlines, Misrair (later Egyptair), and Sudan Airways, it was the most popular Comet variant.

Later service

In 1959 BOAC began shifting its Comets from transatlantic routes and released the Comet to associate companies, making the Comet 4's ascendancy as a premier airliner brief. Besides the 707 and DC-8, the introduction of the Vickers VC10 allowed competing aircraft to assume the high-speed, long-range passenger service role pioneered by the Comet. In 1960, as part of a government-backed consolidation of the British aerospace industry, de Havilland itself was acquired by Hawker Siddeley, within which it became a wholly owned division.

In the 1960s, orders declined, a total of 76 Comet 4s being delivered from 1958 to 1964. In November 1965, BOAC retired its Comet 4s from revenue service; other operators continued commercial passenger flights with the Comet until 1981. Dan-Air played a significant role in the fleet's later history and, at one time, owned all 49 remaining airworthy civil Comets. On 14 March 1997 a Comet 4C serial XS235 and named Canopus, which had been acquired by the British Ministry of Technology and used for radio, radar and avionics trials, made the last documented production Comet flight.

Legacy

The Comet is widely regarded as both an adventurous step forward and a supreme tragedy; the aircraft's legacy includes advances in aircraft design and in accident investigations. The inquiries into the accidents that plagued the Comet 1 were perhaps some of the most extensive and revolutionary that have ever taken place, establishing precedents in accident investigation; many of the deep-sea salvage and aircraft reconstruction techniques employed have remained in use within the aviation industry. In spite of the Comet being subjected to what was then the most rigorous testing of any contemporary airliner, pressurisation and the dynamic stresses involved were not thoroughly understood at the time of the aircraft's development, nor was the concept of metal fatigue. Though these lessons could be implemented on the drawing board for future aircraft, corrections could only be retroactively applied to the Comet.

According to de Havilland's chief test pilot John Cunningham, who had flown the prototype's first flight, representatives from American manufacturers such as Boeing and Douglas privately disclosed that if de Havilland had not experienced the Comet's pressurisation problems first, it would have happened to them. Cunningham likened the Comet to the later Concorde and added that he had assumed that the aircraft would change aviation, which it subsequently did. Aviation author Bill Withuhn concluded that the Comet had pushed "'the state-of-the-art' beyond its limits."

Aeronautical-engineering firms were quick to respond to the Comet's commercial advantages and technical flaws alike; other aircraft manufacturers learned from, and profited by, the hard-earned lessons embodied by de Havilland's Comet. The Comet's buried engines were used on some other early jet airliners, such as the Tupolev Tu-104, but later aircraft, such as the Boeing 707 and Douglas DC-8, differed by employing podded engines held on pylons beneath the wings. Boeing stated that podded engines were selected for their passenger airliners because buried engines carried a higher risk of catastrophic wing failure in the event of engine fire. In response to the Comet tragedies, manufacturers also developed ways of pressurisation testing, often going so far as to explore rapid depressurisation; subsequent fuselage skins were of a greater thickness than the skin of the Comet.

Comet 1

The Comet 1 was the first model produced, a total of 12 aircraft in service and test. Following closely the design features of the two prototypes, the only noticeable change was the adoption of four-wheel bogie main undercarriage units, replacing the single main wheels. Four Ghost 50 Mk 1 engines were fitted (later replaced by more powerful Ghost DGT3 series engines). The span was 115 ft, and overall length 93 ft; the maximum takeoff weight was over 105000 lb and over 40 passengers could be carried.

 * An updated Comet 1A was offered with higher-allowed weight, greater fuel capacity, and water-methanol injection; 10 were produced. In the wake of the 1954 disasters, all Comet 1s and 1As were brought back to Hatfield, placed in a protective cocoon and retained for testing. All were substantially damaged in stress testing or were scrapped entirely.
 * Comet 1X: Two RCAF Comet 1As were rebuilt with heavier-gauge skins to a Comet 2 standard for the fuselage, and renamed Comet 1X.
 * Comet 1XB: Four Comet 1As were upgraded to a 1XB standard with a reinforced fuselage structure and oval windows. Both 1X series were limited in number of pressurisation cycles.
 * The DH 111 Comet Bomber, a nuclear bomb-carrying variant developed to Air Ministry specification B35/46, was submitted to the Air Ministry on 27 May 1948. It had been originally proposed in 1948 as the "PR Comet", a high-altitude photo reconnaissance adaptation of the Comet 1. The Ghost DGT3-powered airframe featured a narrowed fuselage, a bulbous nose with H2S Mk IX radar, and a four-crewmember pressurised cockpit under a large bubble canopy. Fuel tanks carrying 2400 impgal were added to attain a range of 3350 mi. The proposed DH 111 received a negative evaluation from the Royal Aircraft Establishment over serious concerns regarding weapons storage; this, along with the redundant capability offered by the RAF's proposed V bomber trio, led de Havilland to abandon the project on 22 October 1948.

Comet 2

The Comet 2 had a slightly larger wing, higher fuel capacity and more-powerful Rolls-Royce Avon engines, which all improved the aircraft's range and performance; its fuselage was 3 ft longer than the Comet 1's. Design changes had been made to make the aircraft more suitable for transatlantic operations. Following the Comet 1 disasters, these models were rebuilt with heavier-gauge skin and rounded windows, and the Avon engines featuring larger air intakes and outward-curving jet tailpipes. A total of 12 of the 44-seat Comet 2s were ordered by BOAC for the South Atlantic route. The first production aircraft (G-AMXA) flew on 27 August 1953. Although these aircraft performed well on test flights on the South Atlantic, their range was still not suitable for the North Atlantic. All but four Comet 2s were allocated to the RAF, deliveries beginning in 1955. Modifications to the interiors allowed the Comet 2s to be used in several roles. For VIP transport, the seating and accommodations were altered and provisions for carrying medical equipment including iron lungs were incorporated. Specialised signals intelligence and electronic surveillance capability was later added to some airframes.
 * Comet 2X: Limited to a single Comet Mk 1 powered by four Rolls-Royce Avon 502 turbojet engines and used as a development aircraft for the Comet 2.
 * Comet 2E: Two Comet 2 airliners were fitted with Avon 504s in the inner nacelles and Avon 524s in the outer ones. These aircraft were used by BOAC for proving flights during 1957–1958.
 * Comet T2: The first two of 10 Comet 2s for the RAF were fitted out as crew trainers, the first aircraft (XK669) flying initially on 9 December 1955.
 * Comet C2: Eight Comet 2s originally destined for the civil market were completed for the RAF and assigned to No. 216 Squadron.
 * Comet 2R: Three Comet 2s were modified for use in radar and electronic systems development, initially assigned to No. 90 Group (later Signals Command) for the RAF. In service with No. 192 and No. 51 Squadrons, the 2R series was equipped to monitor Warsaw Pact signal traffic and operated in this role from 1958.

Comet 3

The Comet 3, which flew for the first time on 19 July 1954, was a Comet 2 lengthened by 15 ft and powered by Avon M502 engines developing 10000 lbf. The variant added wing pinion tanks, and offered greater capacity and range. The Comet 3 was destined to remain a development series since it did not incorporate the fuselage-strengthening modifications of the later series aircraft, and was not able to be fully pressurised. Only two Comet 3s began construction; G-ANLO, the only airworthy Comet 3, was demonstrated at the Farnborough SBAC Show in September 1954. The other Comet 3 airframe was not completed to production standard and was used primarily for ground-based structural and technology testing during development of the similarly sized Comet 4. Another nine Comet 3 airframes were not completed and their construction was abandoned at Hatfield. In BOAC colours, G-ANLO was flown by John Cunningham in a marathon round-the-world promotional tour in December 1955. As a flying testbed, it was later modified with Avon RA29 engines fitted, as well as replacing the original long-span wings with reduced span wings as the Comet 3B and demonstrated in British European Airways (BEA) livery at the Farnborough Airshow in September 1958. Assigned in 1961 to the Blind Landing Experimental Unit (BLEU) at RAE Bedford, the final testbed role played by G–ANLO was in automatic landing system experiments. When retired in 1973, the airframe was used for foam-arrester trials before the fuselage was salvaged at BAE Woodford, to serve as the mock-up for the Nimrod.

Comet 4

The Comet 4 was a further improvement on the stretched Comet 3 with even greater fuel capacity. The design had progressed significantly from the original Comet 1, growing by 18 ft and typically seating 74 to 81 passengers compared to the Comet 1's 36 to 44 (119 passengers could be accommodated in a special charter seating package in the later 4C series). The Comet 4 was considered the definitive series, having a longer range, higher cruising speed and higher maximum takeoff weight. These improvements were possible largely because of Avon engines, with twice the thrust of the Comet 1's Ghosts. Deliveries to BOAC began on 30 September 1958 with two 48-seat aircraft, which were used to initiate the first scheduled transatlantic services.

 * Comet 4B: Originally developed for Capital Airlines as the 4A, the 4B featured greater capacity through a 2m longer fuselage, and a shorter wingspan; 18 were produced.
 * Comet 4C: This variant featured the Comet 4's wings and the 4B's longer fuselage; 28 were produced.

The last two Comet 4C fuselages were used to build prototypes of the Hawker Siddeley Nimrod maritime patrol aircraft. A Comet 4C (SA-R-7) was ordered by Saudi Arabian Airlines with an eventual disposition to the Saudi Royal Flight for the exclusive use of King Saud bin Abdul Aziz. Extensively modified at the factory, the aircraft included a VIP front cabin, a bed, special toilets with gold fittings and was distinguished by a green, gold and white colour scheme with polished wings and lower fuselage that was commissioned from aviation artist John Stroud. Following its first flight, the special order Comet 4C was described as "the world's first executive jet."

Comet 5 proposal
The Comet 5 was proposed as an improvement over previous models, including a wider fuselage with five-abreast seating, a wing with greater sweep and podded Rolls-Royce Conway engines. Without support from the Ministry of Transport, the proposal languished as a hypothetical aircraft and was never realised.

Hawker Siddeley Nimrod
The last two Comet 4C aircraft produced were modified as prototypes (XV148 & XV147) to meet a British requirement for a maritime patrol aircraft for the Royal Air Force; initially named "Maritime Comet", the design was designated Type HS 801. This variant became the Hawker Siddeley Nimrod and production aircraft were built at the Hawker Siddeley factory at Woodford Aerodrome. Entering service in 1969, five Nimrod variants were produced. The final Nimrod aircraft were retired in June 2011.

Operators

The original operators of the early Comet 1 and the Comet 1A were BOAC, Union Aéromaritime de Transport and Air France. All early Comets were withdrawn from service for accident inquiries, during which orders from British Commonwealth Pacific Airlines, Japan Air Lines, Linea Aeropostal Venezolana, National Airlines, Pan American World Airways and Panair do Brasil were cancelled. When the redesigned Comet 4 entered service, it was flown by customers BOAC, Aerolíneas Argentinas, and East African Airways, while the Comet 4B variant was operated by customers BEA and Olympic Airways and the Comet 4C model was flown by customers Kuwait Airways, Mexicana, Middle East Airlines, Misrair Airlines and Sudan Airways.

Other operators used the Comet either through leasing arrangements or through second-hand acquisitions. BOAC's Comet 4s were leased out to Air Ceylon, Air India, AREA Ecuador, Central African Airways and Qantas; after 1965 they were sold to AREA Ecuador, Dan-Air, Mexicana, Malaysian Airways, and the Ministry of Defence. BEA's Comet 4Bs were chartered by Cyprus Airways, Malta Airways and Transportes Aéreos Portugueses. Channel Airways obtained five Comet 4Bs from BEA in 1970 for inclusive tour charters. Dan-Air bought all of the surviving flyable Comet 4s from the late 1960s into the 1970s; some were for spares reclamation, but most were operated on the carrier's inclusive-tour charters; a total of 48 Comets of all marks were acquired by the airline.

In military service, the United Kingdom's Royal Air Force was the largest operator, with 51 Squadron (1958–1975; Comet C2, 2R), 192 Squadron (1957–1958; Comet C2, 2R), 216 Squadron (1956–1975; Comet C2 and C4), and the Royal Aircraft Establishment using the aircraft. The Royal Canadian Air Force also operated Comet 1As (later retrofitted to 1XB) through its 412 Squadron from 1953 to 1963.

Accidents and incidents
The Comet was involved in 25 hull-loss accidents, including 13 fatal crashes which resulted in 492 fatalities. Pilot error was blamed for the type's first fatal accident, which occurred during takeoff at Karachi, Pakistan, on 3 March 1953 and involved a Canadian Pacific Airlines Comet 1A. Three fatal Comet 1 crashes were due to structural problems, specifically British Overseas Airways Corporation flight 783 on 2 May 1953, British Overseas Airways Corporation flight 781 on 10 January 1954, and South African Airways flight 201 on 8 April 1954. These accidents led to the grounding of the entire Comet fleet. After design modifications were implemented, Comet services resumed on October 4, 1958, with Comet 4s.

Pilot error resulting in controlled flight into terrain was blamed for five fatal Comet 4 accidents: an Aerolíneas Argentinas crash near Asunción, Paraguay, on 27 August 1959, Aerolíneas Argentinas Flight 322 at Campinas near São Paulo, Brazil, on 23 November 1961, United Arab Airlines Flight 869 in Thailand's Khao Yai mountains on 19 July 1962, a Saudi Arabian Government crash in the Italian Alps on 20 March 1963, and United Arab Airlines Flight 844 in Tripoli, Libya, on 2 January 1971. The Dan-Air de Havilland Comet crash in Spain's Montseny range on 3 July 1970 was attributed to navigational errors by air traffic control and pilots. Other fatal Comet 4 accidents included a British European Airways crash in Ankara, Turkey, following instrument failure on 21 December 1961, a United Arab Airlines Flight 869 crash during inclement weather near Bombay, India, on 28 July 1963, and the terrorist bombing of Cyprus Airways Flight 284 off the Turkish coast on 12 October 1967.

Nine Comets, including Comet 1s operated by BOAC and Union Aeromaritime de Transport and Comet 4s flown by Aerolíneas Argentinas, Dan-Air, Malaysian Airlines and United Arab Airlines, were irreparably damaged during takeoff or landing accidents that were survived by all on board. A hangar fire damaged a No. 192 Squadron RAF Comet 2R beyond repair on 13 September 1957, and three Middle East Airlines Comet 4Cs were destroyed by Israeli troops at Beirut, Lebanon, on 28 December 1968.

Aircraft on display

Since retirement, three early-generation Comet airframes have survived in museum collections. The only complete remaining Comet 1, a Comet 1XB with the registration G-APAS, the last Comet 1 built, is displayed at the RAF Museum Cosford. Though painted in BOAC colours, it never flew for the airline, having been first delivered to Air France and then to the Ministry of Supply after conversion to 1XB standard; this aircraft also served with the RAF as XM823. The sole surviving Comet fuselage with the original square-shaped windows, part of a Comet 1A registered F-BGNX, has undergone restoration and is on display at the de Havilland Aircraft Museum in Hertfordshire, England. A Comet C2 Sagittarius with serial XK699, later maintenance serial 7971M, was on display at the gate of RAF Lyneham in Wiltshire, England from 1987. In 2012, with the planned closure of RAF Lyneham, the aircraft was slated to be dismantled and shipped to the RAF Museum Cosford where it was to be re-assembled for display. The move was cancelled due to the level of corrosion and the majority of the airframe was scrapped in 2013, the cockpit section going to the Boscombe Down Aviation Collection at Old Sarum Airfield.

Six complete Comet 4s are housed in museum collections. The Imperial War Museum Duxford has a Comet 4 (G-APDB), originally in Dan-Air colours as part of its Flight Line Display, and later in BOAC livery at its AirSpace building. A Comet 4B (G-APYD) is stored in a facility at the Science Museum at Wroughton in Wiltshire, England. Comet 4Cs are exhibited at the Flugausstellung Peter Junior at Hermeskeil, Germany (G-BDIW), the Museum of Flight Restoration Center near Everett, Washington (N888WA), and the National Museum of Flight near Edinburgh, Scotland (G-BDIX).

The last Comet to fly, Comet 4C Canopus (XS235), is kept in running condition at Bruntingthorpe Aerodrome, where fast taxi-runs are regularly conducted. Since the 2000s, several parties have proposed restoring Canopus, which is maintained by a staff of volunteers, to airworthy, fully flight-capable condition. The Bruntingthorpe Aerodrome also displays a related Hawker Siddeley Nimrod MR2 aircraft.

title: De Havilland Comet