Raïlane Benhacène
email: benhacen@cena.fr

Cockpit Avionics And their perception by Air Traffic Controllers

Keywords: Human factor, avionics, FMS, TCAS, ATC

The perception controllers have pilots' work and working environment is an interesting subject for people working in the field of human factors. Intuitively, it seems that a better understanding of this area may yield interesting results for the improvement of the tools used by both parties to exchange and communicate data, or merely to improve the way they work together. Later applications for the design of new tools could be envisaged, taking these notions into account. This study focused on a specific aspect of the environment, the cockpit avionics. This paper presents the results of a brief survey that was conducted on a sample of 131 French Air Traffic Control Officers (ATCO). Its aim was to try and determine and explicit how cockpit avionics such as FMS or TCAS were perceived and judged or appreciated by ground ATCO. It further tried to explore potential means or ways of enhancing co-operation between controllers and pilots. The underlying expectation was that sharp-end operators, confronted to their task on a daily basis, were likely to have formulated criticisms or remarks on the tools they have to work with, and that this informal but precious and motivated information was seldom passed on to the designer. So the survey was also in part oriented as a call for remarks, suggestions and criticisms on the environment currently in operation. Results show an overall distance and lack of information about these avionics on the ground side. They reveal the potential benefits controllers could draw from having a better knowledge of these tools. The FMS more vividly suffers from this lack of information or training, and data it incorporates are clearly of some interest to controllers. The TCAS seems much better known, and more salient in controllers' perception. Its implementation is clearly felt as the source of added safety, but also an intrusive and sometimes destabilizing intervention, pointing out a problem of lack of clarity as to responsibilities in cases of emergency.

Introduction :

The task an ATCO conducts on his working position is mainly of the cognitive type. To him, aircraft are plots on a radar screen, flight plans which are downsized to be summarised on a paper strip… So, fundamentally, apart from the voice on the radio frequency (admittedly carrying plenty of information and emotion), the ATCO processes information and makes decisions that affect a distant and remote world, and upon which he has little information or 'intimate' knowledge or experience. Adversely, one could also argue that similar distance, not to say ignorance, exists on the other side of the fence. So the fact is that these two highly interdependent worlds ignore almost everything about one another. Being intimately convinced that any means of increasing mutual awareness or knowledge is a potential means of achieving better communication, thereafter yielding an overall better performance (be it qualitative, in terms of comfort, or quantitative, in terms of expeditiousness or amount of traffic treated, or merely but no least interestingly , to enhance a 'natural' prevention of errors or a better recovery thereof), we have tried to establish and get a better feeling of what this perception really consists of. One idea that triggered this survey needs mentioning here. There exists, on any common FMS, a special built-in function called the off-set, which enables the pilot to very easily change the course of his flight trajectory, and shift his flight a given number of nautical miles to the left or to the right. The key point to be remembered here is that the effort, from the pilot side, is minimal, negligible. This function also happens to correspond to a fairly common need ATCOs have, in their daily task. In order to separate aircraft on the same route that are likely, because of a speed difference, to lose separation, they commonly put these aircraft on 'parallel headings'. But the series of actions the ATCO takes to achieve this result in a traditional way is not only lengthy and time consuming, but also yields a significant mental load. The ATCO must first give a heading to direct an aircraft away from his initial route. Then, he must wait a certain amount of time, a 'time lag' until the distance to the initial route is deemed sufficient (say 5 or 8 NM), which can last one minute, or so. Then, and then only, can he give the aircraft his initial heading again, to set it back on a track parallel to its initial course. It this seems easy, one should first bear in mind that if the route legs make an angle some distance further, the new heading needs to be given again. But more than that, the time lag we mentioned earlier, this delay, before 'turning' the aircraft back to its heading, is not free of charge for the ATCO. Even though no action at all is required, memory is solicited to remember the action that is left to be done. And probably some kind of process is initiated, that 'somehow' counts down, or estimates when to 'pop up' again and trigger the adequate action. Even though not visibly solicited, the controller is under workload, far more by all means than with this existing possibility of an off-set which is more of the 'give clearance and forget' type, and which lets his cognition free once said, free and available. In the traditional way of shifting a route, a memorisation an awaiting and a stress are somehow generated. So it is this potential gain and benefit to the controller that has seemed of interest and worth at least some closer examination. Especially knowing how easily and readily close at hand it lies : all it takes is knowing that this function exists, and to think of using it. More generally, our belief is that if one knows of the pilot's environment, tasks, tools, etc., one is more likely to find and use more efficient means to perform his task.

The making of the questionnaire :

❏ -The question was whether or not the Air Traffic Controllers were aware of the existence of such capabilities as the 'off-set' on an FMS. The question is worth considering given the fact that, when asked, some controllers replied by saying that 'probably they wouldn't use this function simply because they are not used to doing so, because it's not part of their habits or practice, etc.' Those same controllers would even reply, when asked about the value added one could expect from sending a questionnaire to learn more about this subject, that one should not expect to get much information from that. In other words : what Air Traffic Controllers know of FMS or cockpit avionics ? Probably not much. ❏ The idea was then expressed that the questionnaire should be expanded to TCAS. Admittedly, controllers have heard of TCAS. They have experienced the existence of such a tool, and have even been confronted with 'problems' or issues related to that tool. And everyone has a feeling or an opinion about the pros and cons of this system, how much 'danger' or 'safety' it introduces into current ATC . ❏ The third type of questions that were introduced into the questionnaire was aiming at determining whether there would be room for a potential cooperation between pilots and controllers via their tools. Some question were therefore elaborated to have controllers explicit if such an idea would please them, or be rejected. Some examples were proposed to illustrate how such a cooperation could take place, and see how those would be appreciated. ❏ The fourth category of questions tried to capture suggestions and to get some feedback as to what needs, ideas or experience controllers could bring from the field of operations. Indeed, it is seldom given for designers of new tools or concepts to have a realistic and faithful feeling about what the workplace really looks like ant what problems are met there. Moreover, knowing that many ATCO are also private pilots, we thought they may have interesting remarks to make on this subject.

So the questionnaire was made of a list of statements which were to be evaluated . Opinions on each statement were to be selected among the following :

Completely Disagree / Rather Disagree / Rather Agree / Completely Agree.

Detail of the questions and the corresponding results is given in appendix.

Population :

The questionnaire was sent to several regional control centres in France, and at two approaches. Further, the questionnaire was also handed to a class of students halfway through their 3-year long training to become ATCOs. So the sample breaks down as follows : Most noticeable facts are the predominance of questionnaires from the Reims Control Centre, which may therefore affect the overall statistics accordingly. One should also bear in mind that the population of this centre is noticeably younger the other centres. Last remark, the students of this sample are in majority assigned to approach control when they finish their studies.

Results and Analysis :

[Question 1 : FMS -You are familiar with the functioning of this tool]. The first and most striking fact is that few ATCOs declare they know this tool well. Less than half of them agree with this statement, the majority remaining more reserved. This, we believe, is rather surprising, when one considers the fact that the FMS went into service on modern aircraft a good 20 years ago. One might be inclined to think that such a tool would by then be fully integrated into the aeronautical landscape. A glance at [Question 23 -TCAS -You are familiar with and understand the logic of the TCAS (TA, RA…)] gives a much more clear-cut answer: a vast majority of ATCOs declares rather knowing and being familiar with the tool (50%) or even better, completely agree (an additional 39%). This results seems rather paradoxical given that TCAS was introduced much more recently than the FMS. Note : FMS appeared since the early 80s TCAS : mandatory equipage since 1994 in the US, year 2000 for ACAS II in Europe, norm which is fulfilled by TCAS II v.7. In other words, and according to ATCOs : we've seen them around since 4 years, more or less.

Even so, this result comes as no surprise : TCAS is more sensitive, since it directly interferes into ATCOs' work, as it make aircraft do things not foreseen by the control. Indeed, and results clearly tell this, this tool very soon impacted aircraft trajectories, and in a very intrusive manner. An aircraft, seen by the controller, and supposed to have and maintain such trajectory, such climb rate, or stable in cruise, suddenly and abruptly changes its course, and deviates brutally from its expected trajectory or path. And as the odds are that part of the control task consists of a surveillance and monitoring process, any aircraft going out of the domain that was attributed to it would constitute a strong trigger of alarm and vigilance. As opposed to this, the FMS which is more devoted to the execution of trajectories planned in the flight plan, seem to act most of the time below the perceptive threshold, and its effect is less visible.

If we look more in detail at this specific aspect, we find out that, in the breakdown of origins for the answers to this question, students of the ENAC school tend to massively answer 'rather agree' to [Question 1] (82%), which leads us to believe that the latter have been granted a training for the FMS tool. Still on this trail, we tried to confirm this result and looked at Reims answers (the youngest centre, with an average of 6 years' experience): surprisingly, the 'completely disagree' answers were the most numerous (37%) of the whole sample. So we wondered whether this could not be explained by the fact that training for FMS was only recently introduced into the curriculum. That would explain this feeling of 'ignorance' even stronger for young ATCOs than for older ones, as the latter have had opportunity to learn some knowledge 'en passant', making flights in the cockpit, on the job training so to speak. We contacted the ENAC school which confirmed :

ENAC : First TCAS training for ATCOs -around 1993 First FMS training for ATCOs -around 1998

Truly, the FMS training wasn't even granted to the youngest controllers of the Reims ACC. This fact pushes them even more radically in the category of people knowing almost nothing of this tool, having not even had the chance to learn in the field. This also explains the result of the answers to So what this is saying is : an ATCO, in order to manage his traffic, build expectations as to the behaviour of aircraft, plausible scenarios of evolution of the situation, to which he associates parameters, criteria or ranges for those parameters. And those parameters only are monitored, and checked for coherence or remaining inside the assigned range. In short, the FMS does not significantly affect these parameters, and is therefore less salient and more easily ignored by the ATCOs. Besides, most common requests for having access to data contained in the FMS where for the Flight Plan Route (cited 18 times for [Question 14]), in the sense that this "FMS flight plan" sometimes differs from the flight plan filed in the Flight Data Processing System (FDPS), i.e. the one they see written on the paper flight strips. This is evidence that the FMS, as a flight management tool, becomes particularly salient and bothersome precisely when it contradicts the expectations of the control, and therefore triggers an unpleasant surprise. Apart from that case, the FMS remains considered as a tool for the pilot, for him to manage 'his flight', whereas an ATCO manages 'his traffic'. Another example to illustrate this : 3 mentions are made in answer to [Question 5 -In general, you think FMS has some potential for simplifying certain situations in ATC / Question 6 -Which ones ?] of the fact that the FMS makes aircraft cut the curves, and smoothes away their trajectory. One answer is even illustrated with a little sketch drawing illustration that aircraft no longer fly vertical of a beacon, but start turning earlier, to be able to reach the second segment of their planned route tangentially. And there are some 'famous' cases when this shortcut is such that the aircraft violates a forbidden zone, a military area noticeably.

The answers to [Question 3 -FMS is an aid for long term navigation] reveal even further this aspect. This question was initially intended to discriminate whether ATCOs thought of the FMS as a tool to manage the flight on the long term, or if they perceived that some punctual clearances could also be managed via the FMS, using the 'selected' mode. Apparently, this question troubled many people. Many question marks or blank responses were made. As for those who answered, they concur to believe the FMS is used for strategic flight or for the long term. (agree rather -69% and completely -23%) The FMS is seldom seen as a tool capable of dealing with the short term, or of being involved in the treatment of an ATC clearance. To this respect, ENAC students are more categorical than the rest of ATCOs. Still on this topic, [Question 12 -You are familiar with the notion of engaged FMS mode (selected, managed)] reveals that there is a clear perceived limit in the tasks and responsibilities sharing. The notions referred to in this question are seen as something belonging to the pilots' domain : this is pilots' work. And truly, more than 60% of ATCOs declare they know nothing about that. Again here, ENAC students are an exception. Contrary to the rest of ATCOs, none of them (0%) declares completely ignoring these FMS mode notions, and more than 80% declare they do know what these modes mean. This can reasonably be attributed to a fairly recent training on the topic. To make a comparison, here are the results for [Question 23 -TCAS -You are familiar with and understand the logic of the TCAS (TA, RA…)] : 50% rather agree and 39% completely agree. Quite an impressive result for a cockpit instrument.

Back to the FMS : [Question 5 -In general, you think FMS has some potential for simplifying certain situations in ATC]. This question brings out all nuances and difficulties that lay between the world of control and that of flying. The answer is rather favourable, but it is a limited agreement. 30% rather disagree with this statement, and 12% completely disagree. They are reserved, and someone even crossed out "simplifying" and marked "complicating" instead. So if apparently some are prepared to acknowledge that this tool may be useful, they are not willing to go too far, in what could be perceived as a 'support' for automation, or even more, as an agreement to 'use' a tool which is and remains of the pilots' side, design and intended to serve their own operational needs. The interesting thing is that the toll of sceptical decreases when answering more precise questions where the FMS is presented as facilitating the work. The example of the route 'off-set' illustrates this quite well : this example is spontaneously cited 27 times in answer to [Question 6]. It seems that ATCOs are more receptive to an operational speech, to the presentation of precise examples. It is then possible to declare with no reserve that yes, in that case, there is an improvement. This seems easier to envisage than to think in a more general way, in principle and approve of a philosophy of tool usage.

A closer look at the answers to this [Question 5], looking at the breakdown by centre, gives a noticeable difference between ACC ATCOs and those of Approach. People in the approach are comparatively less sensitive to the usefulness of an off-set which offers the possibility to shift an aircraft on a parallel route. This function is much better appreciated by en-route controllers obviously as they have to deal with long lasting overtakes. On the other hand, approach controllers are more interested in the ability to make an aircraft follow a holding pattern on any R-Nav point. This is rather logical, given that their work most of the time consists of sequencing aircraft for the runway, in a reduced space, and the possibility of delaying a given aircraft can be very helpful, and corresponds to a common practice and need.

[Question 4 -FMS -When giving a clearance to resolve a conflict, you disturb a flight plan that was scheduled in the FMS]. This question is difficult to use, and in any case does not provide visible benefit. Opinions are mixed, with a slight advantage to positive answers (56% broken into rather -41% and completely -15%). The idea was to check whether ATCOs has a mental image of the FMS Flight Plan as something rigid and frozen, difficult to modify in real time. It seems that there is no such feeling, and that in any case, the ATCOs remains in control, and is in no way affected by the existence of this tool in the pilots' loop.

[Question 9 -FMS -You think the behaviour of pilots has changed since the emergence of this tool] A majority agrees with this ( 75% broken into rather -39% and completely -36%). We can state that the appearance of the FMS has changed something in the French sky. This is not so true for the approach controllers, probably due to the fact that they are in charge of aircraft in a more tactical phase of the flight, during which pilots tend to take over. The details of the following question are more enlightening.

[Question 10 -FMS -Examples] Appendix gives the details of the answers. In general, the examples of pilots' change of behaviour (and in practice, that of aircraft) are more positive (25 answers) than negative (17 answers). Ease and rapidity of reaction of pilots due to the FMS are appreciated. The same goes for precision in trajectories. In other words, ATCOs appreciate what makes aircraft behaviour more reliable, predictable, and conform to their expectations. Adversely, they do not like those features that require lengthy manipulations. This is particularly true for the approach controllers, who mention the "famous" change of runway, presumably a nuisance for pilots, be it on take-off or for landing. More subtly, a criticism is made about this mental rigidity that the FMS may introduce in pilots' minds, in the sense that it makes them focus on their mission, their flight plan, their navigation. This seems to make them less receptive, or aware of the more global and complex task that the ATCOs are in charge of. In this respect, we could re-word it as : the FMS would have increased the gulf between the ground and the board, and would have contributed to their fencing. We can note the slip that occurred here : a criticism of the tool becoming a reproach made to the users of the tool… Nonetheless, we should keep in mind that these negative opinions are a minority, which is illustrated by the following results : [Question 11 -FMS -You think this results is a progress for your work] scores a clear support of this tool ( 80% broken into rather -65% and completely -15%). As a parallel, results for [Question 2 -FMS -You think this tool has had an overall beneficial effect on ATC] gave an overall 87% satisfaction score (broken into rather -68% and completely -19%). So here is strong evidence that controllers appreciate the value of this instrument, and are apparently satisfied with its existence and its intervention in their work. Only the approach controllers stand out for this aspect in being slightly less affirmative for both [Question 11] and [Question 2 ], remaining highly positive however.

[Question 13 -You would find the knowledge of some data in the FMS flight plan useful] ( 70% broken into rather -39% and completely -31%). So we can see that there exists a need for information from the cockpit among ATCOs. The following question [Question 14 -FMS -Examples] gives the information ATCOs mostly expect in order of preference (see Appendix for detail) :

route planned and entered into the FMS flight plan -top of descent -climb or descent rate

The first item is rather annoying : if all went well, i.e. if all pilots had, in their FMS, the same flight plan as the one officially sent to the FDPS, ATCOs should not have to ask for such an information, as they should normally have it on their paper strips. But such is not always the case in practice, and some unpleasant surprises do occur. So this information is requested more for confirmation or contradiction purposes. It is a request for a theoretically already available information, not for a new and missing information.

The top of descent, on the other hand, would constitute a new information for the ATCOs, and which would be of great interest to them. Currently, ATCOs resort to making hypotheses about the point where the aircraft will start its descent. And they do so, in order to anticipate on some traffic situations and the potential conflicts this might generate. Clearly, the pilot, who follows the execution of his flight plan on the FMS, has a more accurate and up to date information. Knowing this information in advance might probably inflict a control decision long in advance, in a very simple way, and allow a better anticipation. In other words, ATCOs see it as a means to be more 'ahead of traffic', and they are willing to take that. The last item is just as interesting : if the radar and the strip provide such vital and accurate information to visualize the geographical position of an aircraft, and anticipate on its future course, the vertical evolution remains the weak point of the representation. And all ATCOs generally concur to say that it is one of the most difficult things to visualise for the following reasons. First, the radar image is 'flat' and therefore not the most convenient thing to get the vertical position information. This information is accessed to via a 'reading' of flight level on the labels, which means using a symbolic representation in the form of a figure. The other reason is that it is very difficult to forecast the climb rate of an aircraft, because this value can vary a lot depending on many criteria. One can easily enough extrapolate the future position of an aircraft in the horizontal plane, given its past positions. It is much more difficult to memorise present and past levels (figures on a label) to infer a rate of climb. More over, depending on the type of aircraft or engines it has, the conditions of the day, the weight of the aircraft, or even airline policy, the rate of climb or descent can vary by an order of magnitude. All this explains why the prospect of having real time access to such a volatile data could surely constitute a good value to ATCOs and a plus for control.

[Question 15 -The knowledge of the FMS flight plan could change some of your control decisions.] also confirms what was mentioned just above, namely the need to have access to up-to-date and relevant information in order to be able to make the best and most judicious decisions. A slight majority -56% -concurs with this statement, but this result is somewhat penalised by the ENAC students' answers. They clearly disagree with the statement, which would otherwise have scored a 63% of positive answers. This result was a good surprise to us, as we feared that this statement be rejected : by questioning the ability of ATCOs to make good decisions, it could have been perceived as slight 'aggression' as it were. This good will, or readiness to question oneself is, in our opinion, reassuring in that it reveals the ability to think back and consider one's daily work with a critical eye, hence an open mind to potential changes as long as these changes are supported by relevant, reliable and up-to-date information.

Similarly, [Question 16 -You believe a better knowledge of the FMS would be useful in your work] reveals the same will and readiness to change. It is almost surprising in this respect, and the consensus is so clear that only 7% of answers disagreed with this statement. This result was not a priori natural, as we could very well imagine that ATCOs be in majority in favour of the FMS ([Question2] and [Question11]) without this necessarily impacting their daily work or customs. Here, clearly, one can see the potential for 'recycling' the tool, for a usage by or a benefit for the ground control. And if we go further along this trail, [Question 17 -FMS -You think this tool could be used to facilitate a cooperation between pilot and controller] we find the same large approval : 79% (broken into rather -49% and completely -30%). It seems a good and generous idea to declare that people should co-operate, help each other etc.

But maybe this is mere lip service that cost little to say ? Not exactly. Evidence for this comes when the same question is formulated for TCAS. The result is just the opposite : no joint utilisation of TCAS by control and pilots. (65% disagree -rather : 23% and completely : 42%). Two elements can explain this last point. First is the regulatory aspects, which we ignored at the time the questionnaire was written. Training for TCAS is very clear about this : on should not use TCAS to make separations, one should not 'cross aircraft' on the TCAS, phraseology such as 'we see him on TCAS' have no legal value and should be banished.

A TCAS expert reviewing the questionnaire jumped on this question and said : this one is a trap. So legally, the rejection of a potential co-operation via the TCAS is normal, and even reassuring. The other reason, which comes from the same origin, is that it is intuitively natural not to get involved in a tool one does not control, and about which one should be careful, as it is likely to step in and counter a control decision, and disturb or complicate an already tense situation. In such case, where a resolution advisory is already urgent and complex to execute, interfering and giving other clearances could put the pilot in a position to chose an option, and could therefore impair his response time. It is therefore safer and sounder to let the TCAS do in such cases, and not to interfere whenever it is triggered, even if one must later take over.

Having established this, we had the intuition that the TCAS would have a poor image among ATCOs, and we expected [Question 19 -TCAS -This tool can yield more security in the flight] to be rejected. Truly, this tool is perturbing and interfering with the classical control, and can ruin a whole strategy that an ATCO was building to resolve conflicts in his sector. Much to the contrary, ATCOs are very supportive of this safety notion and 94% agree (44% rather -50% completely). It is even more evident when phrased in [Question 20 -TCAS -This tool is useful mainly on very short term, occasionally, in emergency] : 97% agree (28% rather -69% completely). So obviously, the TCAS is useful, is perceived as beneficial, and foremost, appreciated as an ultimate protection, a safety device in support of the human operator.

If one stopped there, we could believe that the TCAS is a great invention, and that even ATCOs who are in no way the people for whom this tool was designed, acknowledge the benefits brought by this tool. Some further questions temper somewhat this positive image. [Question 21 -TCAS -You think this tool is an intrusion in your work] 66% disagree (40% rather -26% completely). Not too bad a result, but nonetheless a step down from earlier approval. So the tool is approved of as a safety device, but it is still capable of introducing confusion in the control as is. And here, approach controllers are much more reserved (64% approve the statement 21) and they describe situations where the TCAS complicates a situation, or is poorly adapted to the specifics of approach. Again this comes as no surprise : in a converging funnel leading to the runway, alerts and TCAS interventions are more frequent and more disturbing. Note that some company policies even complicate further this.

But the most surprising thing is that if the majority of other (en-route) controllers are more tolerant towards the TCAS for its intrusive aspect, the concur with the approach for [Question 22 -TCAS -You think some functionalities of this tool can have adverse effects on your task] 74% agree (51% rather -23% completely). So this sheds a different light on the results of [Question 20]. ATCOs acknowledge the merits of this tool, but only in a limited domain : emergency situations, as an ultimate shield against a mistake that could happen to anyone. Nonetheless, this intervention is troublesome, it is not always coherent with the plan an ATCO is conducting, and can therefore sometimes perturb him, reduce his efficiency. One can envisage, and even cite case where the TCAS prompted reactions from the pilot that were not in the direction of greatest efficiency.

Last item about the TCAS : [Question 24 -TCAS -You can easily imagine how a conflict resolution on a TCAS would be perceived by the pilot]. We had in mind the mental image here : we thought that from the ground, it must have been fairly complex to imagine and visualise how the TCAS would yield an effect on the aircraft behaviour. For a better reason, how could one project oneself mentally inside the cockpit, and figure the TCAS instruction. We felt it was crucial to verify this subtle issue, because if such was the case, then there was room for d misunderstanding, poor perception of aircraft situation and conditions, and therefore potentially inadequate decision making. Results tend to show that this worry is not meeting any ATCO concerns : on the contrary, 73% of them think they have adequate image in their minds ( 46% rather agree -27% completely)

The last questions of the questionnaire are more there to give ATCOs a chance to express spontaneously their needs and feelings. As a preamble,

General

Comments on the Questionnaire

The most striking feeling is that a majority of commentaries reveal of a feeling of 'guilt', which prove that this questionnaire was perceived as a test, rather than an opinion poll. The wording that accompanied the questionnaire was of no use : it seems that being questioned on one's professional activity is perceived as inquisitive, or with a judgement in the back of our mind. Our belonging to a the civil aviation authority and being an engineer, traditionally a managing category of personnel, may have caused this. However, we can also consider the likeliness that a number of controllers felt the lack of knowledge of cockpit systems, and conclude that it is a gap worth filling. In the same flow of ideas, many suggestions (whether formulated positively or in a critical way) call for more communications and exchanges with pilots, and to better knowing each other. All go in the same way of a wish for progress, or a concern for the improvement of the way the 'system' works, and again, a willingness to question ones' self which is not often suspected in the body of ATCOs, and probably seldom valued or put forth. To illustrate this, we were often welcomed by sentences such as : 'it's good of you to be interested in what we do', 'not so common', 'if more could do like you' etc. And despite a certain suspicion as to what could be done of what they said; we strongly felt a pleasure people had in talking to us, explaining, discussing, concern about the trade and its future, and many thinking about possible means of improving the work. The habit of working in teams and in shifts with night times or other less busy periods leaving time to discuss probably help this. Last, we need to mention that some comments express a certain suspicion as to what potential changes an inquiry could be hiding. And for example, many ATCOs mentioned that adequate usage of the radio already (and very easily) enabled to get any of those information one might be needing. Similarly, many mention the Data-link technology as being the most natural way for an ATCO to get aircraft data on the ground. Some, though, are concerned about the risk of information overflow, thus drowning vital information that is currently deemed as very useful and familiar. We also noted that the data-link was rather well perceived, but especially because it is seen only from the download perspective : get information from the aircraft, hence potentially get more power to decide. The other way of the exchange, the uploading or sending of data, is clearly never mentioned here… together with a more co-operative attitude (mutual exchange and benefit). In all cases, this circulation of information is technically an advantage, and has positive and useful fallouts on the decision making mechanism. One precaution needs mentioning though : some situations exist where the principle of co-operation can inject more complexity in the system (some TCAS usages illustrate this particularly). Co-operating via the tools, (or simply retrieving distant functions to one's own benefit) are not only inevitable but also fruitful. They reveal the dynamics of integrating a knowledge, appropriating tools, and building of a comfortable, hence efficient, working environment. However, in order to prevent erroneous usage of the tools, training is required to clearly draw the operational limits, and visualise the consequences of actions. Further clarification is therefore needed to make the responsibilities' sharing explicit. We should note that the introduction of a cooperative usage is not necessarily the cause of an ambiguity as to the sharing of responsibilities. It is probably only the catalyst that rendered visible ambiguities already present before the tool or usage were introduced. Ambiguities can cover aspects such as : decision making, responsibility, etc. In other words, the TCAS may have forced the emergence of an underlying, yet very important problematic : the implicit. Who is in control, who is in charge, and above all, who will be pursued if anything goes wrong? This questionnaire reveals, in our opinion, that the situation is unclear, and that the controllers take this opportunity to express their trouble about this.

Another interesting result is the benefit which can be expected from having two communities exchange information. Obviously, much can be improved by superimposing knowledge and data that is currently split between ground and air. Many new ways of working can emerge, without necessarily resorting to complex and sophisticated technologies. To know where a Cumulo-Nimbus is located, or at which rate an aircraft is climbing, are not revolutionary advances, yet they can promote safer or more elegant and expeditious solutions.

We should bear in mind that the tools (or the working environment) described here were designed by an industry whose purpose was to meet a very specific need (the pilots' or the airlines' need). The FMS is thus essentially oriented to flight management to assist the pilot, the TCAS is merely intended as an ultimate protection to safeguard against mid-air collision. So the utilisation of these tools should be cautiously considered. Evidence for this is that training for TCAS was rapidly implemented, more or less simultaneously with its assembling on aircraft. This training was added to ATCOs' curriculum comparatively much quickly than for the FMS.

We believe that this should be considered when designing and /or implementing new devices in the ATC or in cockpits. Considering the global environment should be paramount and considered early enough in the design cycle, by involving different participants or trades concerned. This requires a good understanding, not only of the operational activities of the stakeholders, but also their interest and motivations. In our opinion, this aspect could be just as important as the technical quality and for the success and acceptance of new tools. New tools require a change from operators, a transfer of competence.

It seems that the latest generations of avionics and FMS are designed with an interface embedded to match the ATC phraseology, and make them easier to use in this respect. To achieve this requires rebuilding the interface from scratch to meet this new specification, representing a heavy investment. This evidence supports the concern we have about importance of achieving a common, shared view for different stakeholders. Design needs to be made from a global perspective, larger than the framework of the envisaged activity.

  TCAS, probably because this tool vividly raises some juridical or regulatory questions as to what attitude one should adopt when confronted to a TCAS alarm… The general idea is all embedded in this early result : the point is that one is generally more sensitive to what has an impact on our activity, and sends us a feedback. We then have a sharper image, perceive better, are more led to react at what calls at us. Other information is certainly also perceptible, but experience makes it so that we soon put a filter on this data which reach us, in order to avoid saturation and overflow. We try to save our attention to what deserves treatment, action or analysis from our behalf.

[Question 26 -TCAS -You have had, in you training period, a familiarisation or training for that tool] where more than 70% of ATCOs declare having had, more or less, training about TCAS. Even in ACCs, training courses were set up to familiarize ATCOs with

  Select only those types of information you think you would need, and chose a degree of importance

	Drawbacks Pilots domain,	1	28 -
			(not ATC' s responsibility)
		Too many info is harmful	1
	15 -The knowledge of the FMS flight plan
	could change some of your control decisions
	Completely	Rather	Rather Agree	Completely
	Disagree	Disagree		Agree
	13%	30%	46%	11%
	16 -You believe a better knowledge of the
	FMS would be useful in your work
	4%	3%	52%	41%
	17 -You think this tool could be used to
	facilitate a cooperation between pilot and
	controller
	3%	18%	49%	30%
	18 -You have had, in you training period, a
	familiarisation or training for that tool
	47%	14%	18%	21%
	TCAS
	19 -This tool can yield more security in the
	flight
	Completely	Rather	Rather Agree	Completely
	Disagree	Disagree		Agree
	1%	5%	44%	50%
	20 -This tool is useful mainly on very short
	term, occasionally, in emergency
	1%	2%	28%	69%
	21 -You think this tool is an intrusion in
	your work
	26%	40%	28%	5%
	22 -You think some functionalities of this
	tool can have adverse effects on your task
	5%	20%	51%	23%
	23 -You are familiar with and understand
	the logic of the TCAS (TA, RA…)
	1%	11%	50%	39%
	24 -You can easily imagine how a conflict
	resolution on a TCAS would be perceived
	by the pilot
	6%	20%	46%	27%
	25 -You think this tool could be used in
	conjunction by the pilot and the control
	42%	23%	30%	5%
	26 -You have had, in you training period, a
	familiarisation or training for that tool
	15%	11%	42%	32%
	General
	27 -You think other cockpit instruments
	could provide you with information relevant
	to your work
	5%	11%	54%	31%

Discussion and Conclusion :

The aim of this brief survey was to simply have an idea about the controllers' reality. One of the main results of this study is probably the confirmation that indeed, there is a need for more accurate, up to date information from the aircraft on the control position. And that some benefit could reasonably be expected from having this information that pilots currently have. We have no means to study the way this could be performed nor the social implications this transfer of knowledge would imply. We only point out that a 'predatory' attitude (getting information, i.e. power) exists,

Author Biography :

Raïlane Benhacène is a former Engine and Propeller Certification specialist. He is now working for CENA since 1999. He is involved in the design of new tools for Air Traffic Controllers, and is more specifically interested in the integration of Human Factors in this design. He is currently working on a new concept of tools for Extended TMA

Appendix -Results

FMS :

1 -You are familiar with the functioning of this tool


Benhacene Raïlane

Hurter Christophe

DSNA Marion Anthony

Merlin Bruno

Protectic Rousselle Marie-Pierre

TACKLING THE PROBLEM OF FLIGHT INTEGRATION

Keywords: Air Traffic Control, Flight Integration, electronic stripping, iterative design, HMI, human factor

The work described here is an attempt to improve an electronic stripping for terminal sectors, VertiDigi, in order to design a version dedicated to the Planning Controller (PC). A brief description of the existing tool is done, as well as its design principles. Past experiments are then evoked. They confirm the good acceptability of the tool for clearance input, but also show the emergence of a specific issue: the Flight Integration Process (FIP). This process includes all the mental, physical and manipulation processes that take place between the announcement of a flight and the actual call from the pilot on the radio frequency.

A field observation survey was conducted in summer 2006 in the three Paris Terminal Area centers (Orly, Roissy, and Athis-Mons). The method and tool used to conduct this survey are explained. The data gathered permits a better understanding of this FIP.

From there, an iterative design is started, to redesign the tool specifically to meet this FIP issue. The method involves operators as early as possible, and uses paper or low-fidelity mock-ups to capture their needs. The different steps are listed, and the convergence towards a final new design.

After a brief description of the new design functionalities, the advantages of this design method are discussed, and future experiments are envisaged to validate the HMI.

Introduction

The issue of electronic stripping

Setting up an efficient tool for electronic stripping has been a long standing demand in Air Traffic Control (ATC). Several options have been explored to address this issue. The most widespread one consists in using the radar image, namely the aircraft labels on the radar image, as an input area. This choice means that the Air Traffic Controllers (ATCOs) will use the mouse to click and scroll to select and input the clearances they tell the pilots on the radio-frequency. This choice has several implications:

• Most of the working time will be spent looking up at the radar image (to be compared with current practice: results observed with eye-tracking during Gate-to-Gate experiments [START_REF] Descalle | Gate-to-Gate RTS1B Eye tracking results[END_REF] show that roughly 35% of simulation time is spent looking down at the paper-strips' board). The authors believe that this time spent looking down, although costly, is useful for the building of an accurate and critical mental image of the traffic: it forces the ATCOs to step back from a real-time moving radar image and take a different look at the traffic, anticipating and building a proactive plan instead of a more reactive work.

• Labels being used for input and feed-back result in radar image cluttering, and could jeopardize the analysis of the traffic, and conflict perception.

• Several implicit advantages of paper strips [START_REF] Preux | Functionalities of the paper Strip[END_REF] are lost in the process, because the paper strips bears more than just the input functionality: support for manipulation and planning decisions [START_REF] Mackay | Is Paper Safer? The Role of Paper Flight Strips in Air Traffic Control[END_REF], collaborative work [START_REF] Durso | Following the paper trail: design clues from paper flight Strips[END_REF], [START_REF] Bentley | Ethnographically -informed systems design for air traffic control[END_REF] and workload management for example.

To try and address these aspects, a project (ASTER : ASsistant for TERminal sectors) was started in 2001 to define, for the said terminal sectors, a tool for electronic stripping that would allow rapid input of clearances, while keeping several advantages of paper strips. To do that, some leading principles were adopted. First, a head-down display was selected, dedicated to input and work organization. The idea was to segregate functionalities [START_REF] Norman | The Psychology of Everyday Things[END_REF]; here the analysis display (radar image) from the input and manipulation display, and thus keep interaction on the radar image to a minimum. Then, direct manipulation principles [START_REF] Schneiderman | Direct Manipulation: A step beyond programming languages[END_REF], [START_REF] Rekimoto | Pick and Drop : a direct manipulation technique for multiple computer environment[END_REF] as well as situated cognition principles [START_REF] Hutchins | How a cockpit remembers its speeds[END_REF] were here adopted, to follow the example of a former DigiStrips HMI [START_REF] Mertz | Pushing the limits of ATC user interface design beyond S&M interaction: the DigiStrips experience[END_REF]. This includes touch sensitive input, graphical design, animations, but also possibility to move, manipulate and organize "flight-objects" in a way very similar to what is done with paper strips. Last, these objects have been presented as "labels" displayed on a vertical view of the traffic [START_REF] Benhacene | A Vertical Image as a means to improve air traffic control in E-TMA, Irvine-California[END_REF] to enrich the HMI and give it further representational capabilities in the vertical dimension [START_REF] Lafon-Milon | Représentation mentale de la verticalité au cours du diagnostic dans le contrôle aérien[END_REF]. The resulting HMI has been named VertiDigi [START_REF] Benhacène | As Rapid as Paper Strips? Evaluation of VertiDigi, a new control tool for Terminal Sectors[END_REF] to reflect this combination of vertical view and digital input.

Initial experiments and emergence of the Flight Integration problem (FIP):

The first experiments were conducted in spring 2003, to verify the "workability" of the concept. Several results were derived. The most significant one concerns input: it was deemed satisfactory, and received complete support from ATCOs. The vertical view, although novel and unfamiliar, showed no impact on conflict detection and memorization, and even yielded a significant (40%) reduction in Flight Level clearances [START_REF] Rousselle | Bilan des expérimentations ASTER[END_REF]. Two aspects were criticized, however.

•

The first and minor one was that, for manipulation purposes, each label has a handle and can be moved around on the vertical view in a way similar to the paper strips. When the aircraft moves, however, it "drags" the label behind, which can then overlap another label. ATCOs asked for an automatic anti-overlap. The authors were reluctant to do so, fearing that this would mean losing the manual label manipulation process, and therefore the desired work organization from taking place.

• Second, and more importantly, the ATCOs criticized some design choices regarding the display of some route information. In current paper based environment, when a paper strip is printed, the ATCOs (mostly the Planning Controller (PC)) use it to analyze the flight to come, and make important decisions and anticipation on it. This is called the Flight Integration Process (FIP). The information necessary for this FIP is more 'time-oriented': way-points and time estimates thereupon. But other information is used for this preliminary analysis of the flight: aircraft type, flight origin and destination, etc. This information could not fit into the input-oriented labels we had on the VertiDigi HMI. To avoid overloading the labels, the information was displayed on a dedicated area of the screen: a list on the side of the screen was created, where a series of "mini-strips" was displayed, one for each flight to come. This segregated area would, in the authors' mind, provide the necessary information to the ATCOs when needed.

Experiments showed that this did not work and that ATCOs didn't use those mini-strips. As they phrased it, it is difficult enough to keep a permanent mental link between a radar track and an input label (or paper strip). But to create yet another area just for the FIP is too demanding and generates a high mental workload. As a result, they could not perform an efficient FIP.

Further Testing -the Gate to Gate Real-Time Simulations (RTS3)

In the course of a European project, Gate to Gate [START_REF] Carine | Gate to Gate Simulation Report (Cluster3)[END_REF], the VertiDigi HMI was selected as a tool for the arrival terminal sectors in a large scale simulation. Three (3) terminal sectors where simulated, feeding flights to a series of approach controllers. Each terminal sector was manned by two controllers: an Executive Controller (EC) and a PC; thus a total of 6 VertiDigi equipped position were tested. The results were consistent: even with a dedicated PC position, the FIP was deemed unsatisfactory. Also, input labels' anti-overlap was judged necessary and demanded. Input, which had been further refined and enriched with free text capabilities, was largely approved, and several sequences of traffic were controlled efficiently, sometimes with a traffic load high enough to lead to holding situations.

Field Observation

It was then decided to develop solutions to address this specific issue of FIP, and understand the underlying mechanisms. A field study was launched, in the course of a larger program on the Paris Region. Some observations were done to bring rationale into the design of the PC HMI, and to re-design the PC HMI to address this difficult issue of FIP. The pertaining results are given in next section 'Field Observation: the control room'.

Iterative Design and low fidelity mock-ups

Once the observations were made and compiled, a campaign was started to re-design the interface in order to account for the mentioned limitations and take into account the observations cited above.

The principle chosen is that of participatory, iterative design with users' in the loop. The expectation is that such method will yield a design that is not only quick but also rapidly converging towards the needs of the users, in the hope that this would save development costs and meet the users' expectations as much as possible. The method and the results are given in section 'Participatory usercentred design'.

Field Observation: the control room

This observation campaign was organised in Paris Approach and Terminal Sectors to address several research topics.

Research topics

Four research topics were selected: role and usage of the Arrival Manager, usage of the visualisation tools, role and purpose of the sector to sector coordination, role and usage of the paper strips. In our framework, we shall restrict ourselves to all that concerns the design and integration of strips into an electronic environment. We shall present here the objective, method and results of an investigation in these two directions and which enriched our understanding of the FIP.

Scope of the survey

This survey took place in the control rooms of Paris Approach, in the centres of Roissy-Charles de Gaule and Orly, as well as in the control room of Paris ACC (Athis-Mons). The survey was conducted by 5 observers, lasted 25 days during the period of May to July 2006.

Objective-Tools-Method

The Objective of this survey was to gather as much quantitative as well as qualitative information as possible concerning the real activity of ATCOs.

The way to do this was the definition, beforehand, of a set of observation criteria corresponding to the axes of the survey. These criteria, whenever possible, were broken down into observable (therefore measurable) indicators. The data were collected using a dedicated software Tool featuring ad-hoc observation. The tool was named OUI (Observation User Interface).

This OUI tool allowed a simple counting of certain events (number, duration) which were either pre-defined (observation grid) (e.g. Figure 1) or created dynamically by the observer (e.g. Figure 2). The tool also provided results on the fly, such as average rates of occurrence per observation session, or duration indicators for certain categories of events. This feature was developed to be able to collect unanticipated yet interesting events the observers could discover in the field.

Eventually, the recorded events were consolidated into a data base gathering the observations collected by the different observers.

Qualitative aspects were recorded via interviews, informal discussions with the ATCOs, some individual remarks made by the observers.

The results immediately presented with OUI permitted a debate, and constituted an objective support to the interviews. All these observations and interview notes enabled us to extract the common basis as well as the discrepancies in the role and the utilisation of the strips and the coordination for both approach centres and the centre in charge of terminal sectors.

Figure 1. Predefined Events (Grid) Figure 2. Dynamically created Events

As for the Method, the five observers spent the same number of sessions on all three control centres. Thanks to calendar organization, some sessions featured several observers being present at the same time on two adjacent positions in two different centres. During this three-month long observation period, several debriefings were conducted to better harmonise the observations, specifically regarding the way to timestamp the dynamically created events. Some results have proven relevant, both from the quantitative (thus reliable) and from the informative point of view. A selection of these results will be presented hereunder. A more qualitative analysis of the data and the remarks gathered by the observers will help us propose some directions and thoughts, as well as principles or interaction modes that may be worth developing in the objective of an electronic stripping tool.

Results

We will first give the most reliable quantitative results (over 10 hours of observation). Next, a summary of qualitative results (ATCOs interviews, recurring observation, or important remarks that could not be measured) will be given. Each result is here presented in accordance with its relevance to the topic of FIP in an electronic environment.

Role and purpose of coordination per hour CDG Orly CRNA

Phone coordination (coming in or out) 13 15 19 Cumulated time (minutes) 5 9 7

Table 1. Coordination

This result shows that an average 15 coordination calls are made, per hour, and that this represents an average 7 minutes of activity per hour. Qualitatively, we have observed that the duration of phone coordination lasts noticeably longer in case of misunderstanding, or whenever an uncommon situation occurs (weather, transponder failure on a smaller terrain, problem with mode A). In addition to this, it should be mentioned that a large amount of coordination inside a centre (verbal coordination between two nearby control positions) occur. These can happen between adjacent positions, but also when controllers are more distant. Regarding the role and the utilisation of strips for all three centres in the survey, the strip is above all an item that provides information (e.g. information on the flight, indication of the workload), then a support for memory (e.g. recording clearances given to the pilot), much more than it is a tool for conflict detection.

Role and utilisation of

The strip, in the FIP

We can identify two distinct periods in the life of a strip. One is what takes place before the first call from the pilot, the second stretches from the first contact to the transfer of the flight to the next sector. In the first period, what the PC does in terminal sectors is not really a conflict detection, but rather some anticipation about potential convergence between flights, and also the detection of anomalies on the strip or of some specific and uncommon characteristic of the flight [START_REF] Chabrol | observations au CCR Nord / Roissy / Orly dans le cadre du projet ACROPOLE[END_REF]. This analysis of the strip is conducted in parallel with the sliding of the paper strip into a strip-holder of a given colour, this colour being chosen in accordance with the traffic-flow the flight fits in. This action may seem benign. It constitutes, however, the first mental and physical manipulation of the flight, and contributes to an ideomotor facilitation. The strip is then placed close to the EC strip board, so that the EC may, as a minimum, integrate the flight in his board, and at best, read entirely what information is on the strip. For the EC, this step seems to be what triggers his own representation, but also the beginning of a common representation, shared between the PC and the EC, because it is a visible clue of an informative intention [START_REF] Sperber | La pertinence. Communication et cognition[END_REF].

In order to maintain this common representation, most efforts and demand are placed on the PC. He has to maintain knowledge of the context of the traffic under control, as well as the context of approaching future traffic. This, in order to perform his task as an assistant to the executive controller, such as is the practice in Paris ACC terminal sectors. And he has to do this without the help of manipulation nor direct access to the mnemonic aid, given that the strip does not belong to him any more.

During his initial integration, the PC also determines whether or not coordination is necessary. In view of the observations (see Table 1), coordination is one visible marker of the analysis the PC makes both on the strip and on the radar image. Roughly one in four flights is thus acted upon by the PC.

One other role of the FIP is to give the PC the opportunity to 'graphically' specify a flight, with the intention of sharing information with the EC, before physically handing over the representation of this flight (see Table 2).

In the light of these qualitative observations, further supported by the quantitative indicators, a complete re-design of the HMI was started. We also took advantage of a change in the display technology, which offered new interactions. The principles and understanding we had gathered about FIP and shared context will be used and carried over to the HMI. To do this, we decided to use a participatory design method.

Participatory user centered design

Three objectives were part of the work to be performed at that stage:

• First, even though the observers were familiar with Air Traffic Control, there remains a natural bias in the interpretation of raw data drawn from the observations. To reduce this risk, we confronted our results with ATCOs • Furthermore, we wished to refine the first ideas emerging at the end of the observation stage, and complete them with more specific evaluations • Last, our aim was to improve the VertiDigi application and benefit of the observation results

At first, we have tried to address the following issue: how to efficiently present our results to the ATCOs? The raw data were not explicit enough to be directly questioned by ATCOs. As for the conclusions, they were at risk:

• to be subject of interpretation themselves;

• to be rejected on the grounds of several ready-made prejudices regarding working methods. We therefore decided to complete our observation stage with a participatory design phase [START_REF]Human-centered design processes for interactive systems[END_REF] and a user centred design process [START_REF] Gulliksen | Key principles for user-centered system design[END_REF]. This process enabled us to integrate, in a practical context, the conclusions we had reached through observations, and also permitted to evaluate them. Furthermore, by thus proceeding, we could also refine these conclusions by evaluating new and more accurate derived hypotheses.

Methodology of iterative design

We have organised our method in order to gradually refine the solutions proposed to the ATCOs. This refinement was also organised in order to converge towards our final objective [START_REF] Pekkola | Towards Formalised End-User Participation in Information Systems Development Process: Bridging the Gap between Participatory Design and ISD Methodologies[END_REF]: the specification, in an electronic environment, of the problematic of FIP and of paper strip organisation. This refinement took the form of iterative mock-ups of growing accuracy, which served for small experiments. The results gathered during the evaluation of one mock-up were immediately recycled in the next mock-up and we privileged rapid and numerous iterations rather than deep formal experiments [START_REF] Abras | User-Centered Design[END_REF].

The number of mock-ups necessary was therefore initially not limited, the objective being to iterate as many times as necessary to reach complete satisfaction. In total, 4 iterations were needed. The first two were done with low-fidelity paper-mock-ups and permitted:

• to validate the observations relative to flight integration and the corresponding use of paper strips • to determine the driving principles to be followed in order to carry over flight integration in an electronic environment.

The next two mock-ups, which were done in a software version this time, permitted:

• to complete and improve the FIP and the strip-organisation in an electronic environment;

• to evaluate complementary and additional solutions on how to share a context in such an electronic environment;

• to converge on technical and hardware solutions which would serve as the foundation of a new version of VertiDigi.

First round

The first iteration thus featured five low fidelity mock-ups (paper mock-ups), each of these reflecting the FIP as it was perceived by five different participants. These five persons either had participated in the on-site observations, or had built a mock-up to reflect their own understanding of the conclusions that came out of the field observation stage.

Figure 1. One of the 5 paper mock-ups

In this context, it was difficult to organize a rigorous and formal evaluation of the mock-ups. We therefore proceeded with a qualitative evaluation. Ten ATCOs compared the different mock-ups.

Working scenarios were run on each mock-up, with each ATCO. The interviews conducted after each run were then summarized and enabled the selection of two possible FIPs.

Second round

The second iteration was thus the continuity of the former one, and confronted two different strategies for FIP and for Executive/Planning controller cooperation.

The first strategy enforced a strongly scheduled organisation of the work. Each step of the work was performed in a separate and physically distinct locus on the workspace. The sequence of work was organised as follows:

• The paper strip was initially present to the PC.

•

The latter could perform an initial integration of the strip, colour the strip according to the flow it belongs to, and, if necessary, coordinate the conditions of delivery of this flight with the former sector.

• After a given amount of time buffering (depending on the EC workload and availability), the PC transferred the flight object to the EC.

•

From then on, a parallel work could take place on two distinct yet synchronized instances of the strip: the EC made input of clearances on his own, while the PC could still make exiting coordination (with the next sector).

• Last, the strip was transferred by the EC to the next sector.

The second strategy was somewhat more permissive. First, the organization of work was not constrained by any particular workspace on the HMI. Furthermore, the EC was given the possibility to by-pass the initial integration (normally allocated to the PC) and organize this integration himself.

Figure 2. One of the mock-ups of iteration round 2

The two strategies were each reflected in a separate mock-up. These mock-ups, which were more detailed and elaborate than in the former round, were then submitted to a similar evaluation as in the first iteration.

The least constraining strategy eventually obtained a comprehensive support from the participants.

Third round

The fact is that each controller was allocated a copy of the flight instead of one paper strip for both controllers (as is the case nowadays). The main objective of this round was thus to evaluate whether this would cause problems in terms of context sharing for the pair of controllers.

This evaluation stage was performed on a lightweight and simplified software mock-up (Functionalities were kept to a minimum). Controllers could thus only input coordination (on the PC side) or pilot clearances (EC side), and each side could move and organize its strips:

• Either independently, each on his own screen representation of the strip board,

• Or in a "synchronous" way. In this case, any strip moved by the EC on his screen was simultaneously moved on the PC side (and the other way around)

Figure 3. EC and PC HMIs

The second way was triggered on the PC side by an action which consisted in « metaphorically » capturing and dragging the EC HMI on his own side.

Figure 4. PC gradually captures the EC HMI

The controller pairs thus played working scenarios with two different manipulation modes. A third session offered them a free mode, in which they could alternate from one mode to the other.

Several aspects contributed to a clear preference for the 'non-synchronized' mode of strip movements:

• Except in some rare occasion when the EC permits the PC to shift some of 'his' strips on the board, the PC never moves the strips himself. The EC must be able to find the strip at the place where he had positioned it himself.

• Each controller being focused on a different aspect of the traffic, free individual positioning gave them the possibility to organize strips differently, according to their own priorities.

•

The fact that both HMIs are located nearby still give the PC the possibility to check and verify the EC organization when needed.

Last design round

This iteration did not bring forward any new element or design feature, but it was the opportunity to materialize and bring together different elements resulting from earlier rounds. The result was implemented on a mock-up derived in two versions: an EC and PC side. This enabled the pair of ATCOs to manage all cases they meet in their nominal working practice.

Result of the iterative design method

Being, as it is, a compromise between a formal evaluation and a simple design run, this user-centred iterative design [START_REF] Iivari | Varieties of User-Centeredness[END_REF] granted us two objectives we had in mind.

We have first been able to confront our field observations with the ATCOs, as well as the conclusions we had come up to at the end of the said observations. The choice of paper mock-ups was an easy and very efficient way to evaluate various choices and rapidly converge on a solution. This method, besides, was very simple and saved us sizeable development costs. Furthermore, this method was a way to gradually validate a migration of the FIP into an electronic environment. And, thanks to a relevant design process [START_REF] Schlienger | Une experience de conception et de prototypage d'interfaces évoluées en milieu industriel[END_REF], which provided us with a technical method to support participatory design, we have laid the first stone of a new version of our HMI.

Last, the users appreciated this method involving them in the early design, and were happy to contribute.

Conclusion

The new design of the VertiDigi HMI was driven by the needs and drawbacks of the earlier version. Through the debriefings with ATCOs, we were forced to tackle this longstanding issue and aspect of the flight strips: the Flight Integration Process. We are not aware of any kind of electronic stripping (typically input conducted on the radar image and in the radar labels) that addresses this issue of FIP.

It appeared that the provision of elementary information needed to perform this FIP was not a sufficient solution: a better understanding of the physical location of this information, the way it was coded, and the way it is collected, shared and passed along can be significant. In other words, devil is in the details. Being aware of the importance of these aspects, it becomes fairly natural to try and respect them as guidelines, when it comes to designing an electronic stripping.

In practice, the new design includes several features:

• on the PC side, in the upper left corner, a special 'box' is placed. It serves as arrival dock for flights. A short label appears there whenever the Flight Data Processing System emits data concerning a new incoming flight,

• Optionally, this 'box' can be captured by the EC on his own screen, to account for fact that the EC sometimes does the integration process himself,

•

In nominal mode, the PC extracts a label passing through a coloured gate (red or green) which 'taints' the label. This reflects the flight belonging to a certain flow, but also to implicitly inform the EC that this initial analysis was done,

•

The label expands to become a strip, complete with route information,

•

The PC can further analyse potential problems with the flight, and perform any coordination needed,

• After a given time buffering (depending on workload), the PC physically passes the strip from his display to the EC display,

• The strip appears in condensed format on the PC side.

•

The PC has clues about coordination performed, as some minute arrows indicate input fields concerned with coordination,

• He can either expand the strip to check them or proceed with his current practice and check them later, as appropriate,

• Last, the two displays are non-synchronous, and each controller can arrange strip to match his own needs.

Figure 6. PC display (final design)

Several techniques and principles have been used, pertaining to the field of HMI, in order to give operators a feeling of comfort and familiarity when they get to work in a new environment. The most obvious advantage of this participatory and iterative method is its cost effectiveness and rapidity. In fact, it appears that low fidelity mock-ups constrain the designers into allocating more time to the end-users and operators. Their repeated involvement in the early design steps helps eliminate bad design options very early in the process. This saves a great amount of development and design efforts.

Plus, the users take active part in the design, and often come up with unexpected suggestions as to how an interaction should be done, and what priorities to allocate to different functionalities. In our case, it is interesting to remark that they have naturally chosen the more permissive and open philosophy for the interface. This means that their comfort is higher whenever there is room for flexibility, adaptability to cover unexpected situation etc. In short, a proper design is often one that is flexible enough to allow adaptive usage, not necessarily a comprehensive and very accurate one. Unexpected or non nominal situations being standard practice in air traffic control, this choice comes as no surprise.

Last, it is to be noted that the final design was obtained only by mimicking the current practice on paper strips. Naturally, the electronic environment allowed room for more creative and newer tools and working methods. However, this 'chameleon' option seems to be the one to grant better acceptance. Above all, it ensures a safe transition and preserves current practice and working This means easy transition, quick training, lower stress and lower feeling of disorientation. These aspects alone are sufficient to drive the choice of end-users.

The result is an interface which is, to say the least, acceptable to users for what they perceive as their future work in an electronic environment.

This expectation now needs to be confirmed in further testing, using real time simulation which should be conducted early summer 2007.

Figure 5 .

 5 Figure 5. EC and PC Mock-Up A pseudo-pilot and lightweight simulator connected to the HMIs made it possible to simulate the behaviour of aircraft and R/T communication with pilots to enhance the realism of the situations played. This new evaluation enabled us to confirm the choices made earlier. It also brought forward a

Table 2 . Srip Management

 2

		Strips
	Number (per hour)	CDG Orly Paris ACC
	Strip highlighting	15	2	8
				All strips
	Strip handover	22	26	(PC to
				EC)
	Moving strips on the board	43	27	20
	Writing on strip	76	30	114