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The instrument explosion — a study of aircraft cockpit instruments
AppliedErgonornics 1977, 8.1, 23-30
The instrument explosion- a study of aircraft cockpit instruments E.J. Lovesey Human EngineeringDivision, Flight SystemsDepartment, Royal Aircraft Establishment, Farnborough, Hants.
Aircraft cockpit instruments have been increasing in number since the Wright Brothers made their first powered flight. As aeroplane development progresses, new systems are continually being added to improve performance or capability and cockpits have now reached the stage where there is often little space left in which to install the monitoring instruments for these additional systems. Fortunately, the advent of electronic cockpit displays offers a solution to this problem. One electronic display can be used to present the information previously requiring several conventional electro-mechanical instruments, with a consequent saving in cockpit panel space. However, cockpit displays must be matched to the pilot's information requirements and processing abilities. If this is not done the advantages of electronic displays will not be realised and the pilot will be in an even worse position than he was before.
Historical trends When the original Wright biplane flew, it contained just a stopwatch, a tachometer and an anemometer (Chortey, 1976). However, these were used to help the Wright Brothers measure performance, rather than as 'cockpit' instruments to provide flight information. Before long, as more aeroplanes appeared, most cockpits contained the rudimentary flight instruments of compass, air speed indicator~ altimeter and engine revolution counter. (See Figs. 1 and 2). The First World War gave impetus to instrument development and by its end the
number of instruments in some cockpits, such as is shown in Fig. 3, had reached double figures. (Coombes, 1972 74.) While most of these early aeroplane instruments were relatively crude and had poor displays, a few had surprisingly good features. The features of the poorer instruments were railway line markings, (see Figs. 1, 2 and 3) overnumbering, numbers outside the scales resulting in smaller graduation separation, 'gas meter' type sub-dials within a dial (see Fig. 2), dials crowded with graduation marks, small, ornate or indistinct
Fig. 1
Simple cockpit layout of World War I aeroplane,circa 1916
Applied Ergonomics
March 1977
23
Fig. 3
24
Fig. 2
Early instrument panel showing both good and bad features
Fig. 4
A "Pioneer" instrument panel of 1925 showing early use of strip displays and a well designed counter-pointer air speed indicator
De Havilland 9Abomber cockpit. Note the increase in the number of instruments by 1918 and the individual instrument lights for night flying
Applied Ergonomics
March 1977
figures, excessively thin pointers and shiny brass bezels (see Figs. 1,2 and 3). Sadly, some of these features are still to be found in aircraft flying and in service today. Among the better features often to be seen in the early aeroplanes were the clear numbering and graduation markings (as seen in the altimeter of Fig. 2), scales numbered in multiples of 1 or 10 and sub-divided by 10 intervals, contrasting white numerals and graduations on a matt black dial as in the altimeter and revolution counters respectively, shown in Fig. I. Both the good and the bad features have been perpetuated in aircraft instruments until quite recently. At last, present aircraft instruments are free from the more obvious poor design features, but vigilance must be exercised to ensure the current standard is maintained or improved. There is still the danger that instruments will be designed in accordance with the dictates of fashion rather than with the requirements of good ergonomics practice, and fashions tend to go in cycles. It is interesting to note that both the excellent counter pointer instruments and the questionable strip (or tape) instruments have come into aircraft cockpits at frequent intervals throughout aviation history. The 1925 Pioneer instrument panel shown in Fig. 4 contains both strip displays and a counter pointer air speed indicator which bears a remarkable resemblance to the modern counter pointers shown in Figs. 8 and 9. Both types of instruments lasted for a few years, were rejected and disappeared for perhaps a decade or more before re-appearing again. By the start of World War II, strip instruments were on their way out. By 1939 the Spitfire Mark I cockpit shown in Fig. 5 contained only two strip instruments. (Rolfe, 1964.) It also had the RAF 'basic six' instruments for blind flying. These six instruments, air speed indicator, artificial horizon, rate of climb indicator, altimeter, directional gyro, and turn and bank indicators, were, from 1938 to the early 1950s, to be seen as a central feature in most UK military aircraft. The 'basic six' has now been replaced by the 'basic T'. In this the air speed indicator, attitude direction indicator and altimeter form the top of the T, and the horizontal situation indicator forms the tail, as depicted in Fig. 9.
Strip instruments As indicated above, the choice of strip displays for an aircraft would appear to depend on current fashion rather than on good ergonomics reasons. Strip displays are certainly more difficult to read than conventional dial and pointer instruments, especially under the vibration conditions to be found in helicopters. One can always detect the approximate angular position of a pointer on a circular dial, no matter how blurred it might appear due to vibration. The pointer's position on a strip instrument is far harder to sense, and usually will have to be very carefully read since it is more difficult to detect linear movements and positions than angular ones. This is particularly so if low frequency vibration (ie, 1-30 Hz) is present. Vibration blurred scales and pointers on a strip display can form nodal images which are difficult to relate to one another. An argument often put forward in favour of strip displays is that if used, for example, in multi-engined aircraft to show engine speed under normal operating conditions, the vertically mounted strips can be scanned along, and any
Fig. 5
Sptifire Mk I cockpit of 1939, with the 'Basic Six' blind flying panel
deviation from the norm on one engine can be detected immediately. This form of scanning for faults, has, of course, been used in cockpits for many years with circular dial and pointer instruments, by rotating the instruments in their mounting until the pointers are horizontal at the 3 o'clock position for normal operating conditions. As one leading instrument manufacturer states, (Anon, 1976) "Although the vertical tape instrument has some advantages over the circular scale instrument it sometimes presents a problem when allocating panel space because of its awkward shape as well as presenting an ergonomic problem when used in serried ranks; when the pilot might not always be able to sort out quickly which of the many vertical lines is the one with which he is immediately concerned." It is interesting to note that while the present generation of wide body American transport aircraft cockpits contain strip instruments, the cockpit mock-up of the future 'NASA/ Boeing terminal configured vehicle' contains only conventional circular scale instruments and two electronic or cathode ray tube (CRT) displays.
Applied Ergonomics
March 1977
25
Fig. 6
Fig. 7
Mosquito NF Mk 38, showing early use of CRTs and intrusion of systems into the cockpit, circa 1950
Systems and the exponential rise in the number of instruments The coming of the jet engine did not, in itself, radically change the number or type of cockpit instruments. Perhaps the greatest change, certainly as far as numbers of instruments and switches are concerned, was due to the new and advanced systems which began to appear towards the end of World War II. The Vampire jet aircraft's cockpit, shown in Fig. 6, differs little from that of the earlier Spitfire, but the night-fighter cockpit of Fig. 7 is really beginning to take on a different appearance with its early cathode ray tube display for radar. This cockpit shows the transition from the earlier generation, with its 'basic six' blind flying panel (centre left) and gas meter type dial (right), to the modern systems hardware of CRTs and rows of switches and contact breakers (upper right). Fig. 8 represents typical cockpit layout of the 1960s with almost all of the cockpit panel space taken up by instruments, lights and switches. In fact, some additional instruments, which intrude into the pilot's external vision
26
Vampire Mk 20 cockpit, little different in basic layout to the Spitfire a decade earlier
AppliedErgonomics March 1977
area, have been added above the cockpit combing. One reason for the massive increase in cockpit instruments and switches is that for the past decade or so, an aircraft type might have a useful working life of 20 years or more (eg, Hunter, Canberra, Phantom). During this time the aircraft's role might change from, say, a high altitude fighter to a low level strike aeroplane. The cockpit layout might have been optimised at the start for use as a fighter, but as the role has changed, so new systems have been added, which has required additional instrumentation to control and monitor them. This has led to very cluttered unergonomic cockpit layouts and an almost exponential rise in the number of instruments, as shown in Fig. 10. A single seat cockpit of the modern strike aircraft might contain over 300 instruments, indicators, controllers and switches (Shaw and Port, 1972; Fozard, 1969; Harlow, 1974). This rise in the number of systems (and therefore instruments to be monitored) has been accompanied by an increase in aircraft speed and performance (see Fig. 11). This increase in speed has served to aggravate the pilot's task. Now he not only has more instruments to monitor, but
The technology is now available in the form of CRT displays, to present only that information that is currently required. With a CRT display, the pilot will probably be given the basic flight information of airspeed, altitude, attitude, and heading (as normally displayed by the 'basic T' layout). He will then select other quantities such as engine parameters and check lists to be displayed, while system malfunctions could be programmed to be presented to him automatically. At present, aircrew often have to carry a bagful of manuals for route navigation, radio frequencies, check lists and emergency procedures with them to the aircraft. These sometimes present stowage problems in the cockpit. The suitably programmed CRT disply offers an elegant solution to this problem. Fig. 12 shows a typical pre-flight check list. Note that the operator has had to interact with the system as he works through the list. Dots have appeared against the first four items that he has checked. He now has to check 'probe heat' and if satisfied with it he will press the appropriate button and move on to the next check. If he misses the check the system will warn him of his error.
Fig. 8
Example of pilot's cockpit of an aeroplane in service today
In addition to these uses, the CRT display of basic flight information might be combined with the low light television view of the outside world for night operations, (see Fig. 13). This is alright as far as it goes, but has the disadvantage that the pilot has to look inside the cockpit at this head-down display with its limited field of view. He may have to time share between this display and the outside world.
less time in which to do so. It has been estimated that if the recent exponential rise in the number of cockpit instruments continues, by the 1980s cockpits will contain between 200 and 300 instruments. Fortunately, a solution is already at hand, in the form of multifunction CRT and other types of electronic displays.
Current and future cockpits There are many ways of saving panel space or reducing the number of instruments in the cockpit. Some methods are good, some are less than good, and even dangerous. For example, two- or three-pointer instruments are used. These instruments certainly save space, but sometimes at the cost of greater reading difficulty and increased errors. The fatal accidents which have been caused by misreading the threepointer altimeter are well-known examples of the results of poor display design. The modern single-pointer altimeter combined with a digital readout overcomes most of the problems associated with the three-pointer instrument, giving both precise height and rate of change of altitude information clearly and unmistakably.
Simple status indicators such as lights can sometimes be used to save space by replacing bulkier dials. Often the pilot or flight engineer needs only to know whether the system is within limits, which can be indicated by warning lights. He does not need to know the precise state of the system which requires a dial to indicate it. Even when he does need to know a precise value of the system that he is monitoring, he may need to check it only once or twice per flight. For the rest of the time the instrument is cluttering up the cockpit and possibly acting as a distraction to the pilot.
Fig. 9
Lynx helicopter cockpit, 1974, showing trial layout of strip and conventional circular instruments
Applied Ergonomics March 1977
27
-!
60~ 50 "u)
×
40-
/ X ~X
E
"6 Z
v×Af Jo
~ y /×x
1900 I0
20
~
40 50 Yeor
60
70
Fig. 10 Cockpit instrument growth. Fixed wing, single seat fighter t y p e aircraft
. . . . . . . . . . . . . . . . . . . . . .
200£
1800
•
-
•
•••
0~ =E 1200 ._c
The helmet mounted display (HMD) could be described as the ultimate development of the helmet mounted sight which itself comes mid-way between the HUD and HMD. The helmet mounted sight consists of a boresight with a limited amount of extra information added to it. The device is collimated and provides a simple display in front of the operator's eye. Figs. 15 and 16 show a typical helmet mounted sight and an example of the clear presentation that might be produced in front of one of the eyes of the pilot. It is designed to improve man's ability to aim weapons or sensors at potential targets by merely looking in the target's direction; sensors within the cockpit detect the
10£x3 E
o 800 ~E o
400
Despite the potential advantages of CRT displays, and other electronic displays such as LEDs (light emitting diodes), LCDs (liquid crystal displays), plasma panels, etc, there is the danger that their full value will not be realised. The tendency to try to put too much information on the display is strong and must be countered by good ergonomics guidance. Since man is effectively a single channel device, albeit one that time shares, there is little to be gained by trying to present him simultaneously with all of the information he needs throughout the entire flight. He can only process a relatively small amount of it at any instant, even when working at peak capacity. Under periods of extreme stress his processing rate may be even further reduced and a surfeit of signals will in no way help him to return to his previous higher processing rate. This excess of signal presentation is already occurring with some instruments such as HUDs, hehnet mounted sights and displays.
t600 1400 --
spent looking within the cockpit will reduce his chances o~ making a safe landing. Thus, a HUD can be of immense benefit in some, otherwise, marginal situations. In addition, the HUD has another advantage that its collimated image bestows. Since the image is presented at infinity, it is Less affected by vibration than conventional head-down instruments, as Fig. 14 so obviously shows. Despite its obvious advantages, the current HUDs have the serious shortcoming of an inadequate view. Only a small part of the outside world can be seen through the HUD 'porthole'. This results in HUD clutter which could be reduced if a larger field of view could be provided.
!
200 0
Fig. 11
1900 t0
20
30
40 Yeor
I 50
I 60
I 70
Maximum speed of single seat aircraft w i t h date of entry into service
Alternatively, information may be superimposed on the real world outside by using a head-up display (HUD). In this display the CRT image is projected onto a screen in front of the pilot and collimated, so that he sees the information 'outside' the cockpit at infinity. (See Fig. 14.) This enables him to maintain his view of the outside world without having to spend time to look 'head-down' and search for information from the conventional panel mounted instruments. The HUD is particularly useful when, for example, approaching a runway in fog where the pilot needs to keep his eyes skinned. In this situation, the pilot has little time to see and to recognise the runway and then to decide whether it is safe to attempt a landing. Any time
28
Applied Ergonomics
March 1977
Fig. 12
Typical check list, illustrating the versatility of the C R T display
Fig. 13 A possible CRT display format of basic flight ird~,ormation superimposed on a I'ow liigh.t TV view of the outside world
Fig. 14 Collimated Head-Up-Display image, illustrating clarity of information presentation in a vibrating environment
Fig. 15 A first generation Helmet Mounted Sight
Fig. 16 Pilot's eye view with Helmet Mounted Sight
Applied Ergonomics
March 1977
29
The HMD is a far more complex device which produces a complete display in front of one eye of the pilot (see Fig. 17). leaving his other eye free to view the real world. Figs. 18 and 13 show the sort of images that might be presented on an HMD. It has been claimed that by presenting a collimated display directly in front of the eye, information can be displayed over a far greater area than can be done by HUDs or panel mounted instruments, whose area is limited by the need for windscreens and cockpit controls. While the HMD is potentially a most useful device, much of the design effort, so far, seems to have gone to maximising the amount of information displayed to the man. Few seemed to have questioned whether it is the correct information or how much of it a man can process. Unless these aspects receive the attention that they clearly deserve, the future pilot will be presented with more and more information which will be utilised by him less and less. The cost and complexity of his displays will increase and so will his workload, but the overall efficiency of the man-machine system will decline due to ergonomic shortcomings of the display interface.
Acknowledgements The author would like to thank Marconi Elliott Ltd and Smiths Industries Ltd for their permission to use their material for some of the text and illustrations in this paper.
Fig. 17 Second generation Helmet Mounted Display
© Copyright Controller HMSO, London, 1976.
References Anon 1976 Smiths Industries Aviation Review, Evolution of the instrument panel, 32, 19-20, 34, 14-16. Chorley, R. 1976 "70 years of flight instrument displays". The third HP Folland Memorial Lecture. Royal Aeronautical Society London. Coombs, L.F.E. 1972-74 Air Enthusiast, February, June and November 1972, pp 6 3 - 6 7 , 2 9 1 - 2 9 3 , 2 3 7 - 2 4 0 ; April and October t973 pp 1 8 8 - 1 9 1 , 1 7 2 - 1 7 6 ; a n d August 1974, pp 84-87. Front Office Evolution 1-6.
Fozard, J.W. Fig. 18 A typical pilot's eye view through a Helmet Mounted Display
position of the helmet and feed data to a computer which then calculates where the man is looking and finally programs the weapon system where to point. At present, the helmet mounted sights appear to present about the right quantity of data to the man. However, as the helmet sighting systems develop again, there will be the tendency to try to present more and more information around the sight. Eventually this will clutter up the display and reduce some of the sight's present advantages of clear presentation.
30
AppliedErgonomics March 1977
1969 The Harrier. J.D. North Memorial Lecture, Royal Aeronautical Society, London. Hadow, P.G. 1974 A comparison of the number of cockpit displays and controls in 8 military helicopters. Unpublished RAE Report.
Rolfe, J.M. 1964 The fighter cockpit 1910-1963. RAF IAM Report No 222.
Shaw, M., and Port, W.G.A. 1972 A comparison of the number of cockpit displays and controls in 6 military aircraft. RAE Report TR 82140.
The instrument explosion- a study of aircraft cockpit instruments E.J. Lovesey Human EngineeringDivision, Flight SystemsDepartment, Royal Aircraft Establishment, Farnborough, Hants.
Aircraft cockpit instruments have been increasing in number since the Wright Brothers made their first powered flight. As aeroplane development progresses, new systems are continually being added to improve performance or capability and cockpits have now reached the stage where there is often little space left in which to install the monitoring instruments for these additional systems. Fortunately, the advent of electronic cockpit displays offers a solution to this problem. One electronic display can be used to present the information previously requiring several conventional electro-mechanical instruments, with a consequent saving in cockpit panel space. However, cockpit displays must be matched to the pilot's information requirements and processing abilities. If this is not done the advantages of electronic displays will not be realised and the pilot will be in an even worse position than he was before.
Historical trends When the original Wright biplane flew, it contained just a stopwatch, a tachometer and an anemometer (Chortey, 1976). However, these were used to help the Wright Brothers measure performance, rather than as 'cockpit' instruments to provide flight information. Before long, as more aeroplanes appeared, most cockpits contained the rudimentary flight instruments of compass, air speed indicator~ altimeter and engine revolution counter. (See Figs. 1 and 2). The First World War gave impetus to instrument development and by its end the
number of instruments in some cockpits, such as is shown in Fig. 3, had reached double figures. (Coombes, 1972 74.) While most of these early aeroplane instruments were relatively crude and had poor displays, a few had surprisingly good features. The features of the poorer instruments were railway line markings, (see Figs. 1, 2 and 3) overnumbering, numbers outside the scales resulting in smaller graduation separation, 'gas meter' type sub-dials within a dial (see Fig. 2), dials crowded with graduation marks, small, ornate or indistinct
Fig. 1
Simple cockpit layout of World War I aeroplane,circa 1916
Applied Ergonomics
March 1977
23
Fig. 3
24
Fig. 2
Early instrument panel showing both good and bad features
Fig. 4
A "Pioneer" instrument panel of 1925 showing early use of strip displays and a well designed counter-pointer air speed indicator
De Havilland 9Abomber cockpit. Note the increase in the number of instruments by 1918 and the individual instrument lights for night flying
Applied Ergonomics
March 1977
figures, excessively thin pointers and shiny brass bezels (see Figs. 1,2 and 3). Sadly, some of these features are still to be found in aircraft flying and in service today. Among the better features often to be seen in the early aeroplanes were the clear numbering and graduation markings (as seen in the altimeter of Fig. 2), scales numbered in multiples of 1 or 10 and sub-divided by 10 intervals, contrasting white numerals and graduations on a matt black dial as in the altimeter and revolution counters respectively, shown in Fig. I. Both the good and the bad features have been perpetuated in aircraft instruments until quite recently. At last, present aircraft instruments are free from the more obvious poor design features, but vigilance must be exercised to ensure the current standard is maintained or improved. There is still the danger that instruments will be designed in accordance with the dictates of fashion rather than with the requirements of good ergonomics practice, and fashions tend to go in cycles. It is interesting to note that both the excellent counter pointer instruments and the questionable strip (or tape) instruments have come into aircraft cockpits at frequent intervals throughout aviation history. The 1925 Pioneer instrument panel shown in Fig. 4 contains both strip displays and a counter pointer air speed indicator which bears a remarkable resemblance to the modern counter pointers shown in Figs. 8 and 9. Both types of instruments lasted for a few years, were rejected and disappeared for perhaps a decade or more before re-appearing again. By the start of World War II, strip instruments were on their way out. By 1939 the Spitfire Mark I cockpit shown in Fig. 5 contained only two strip instruments. (Rolfe, 1964.) It also had the RAF 'basic six' instruments for blind flying. These six instruments, air speed indicator, artificial horizon, rate of climb indicator, altimeter, directional gyro, and turn and bank indicators, were, from 1938 to the early 1950s, to be seen as a central feature in most UK military aircraft. The 'basic six' has now been replaced by the 'basic T'. In this the air speed indicator, attitude direction indicator and altimeter form the top of the T, and the horizontal situation indicator forms the tail, as depicted in Fig. 9.
Strip instruments As indicated above, the choice of strip displays for an aircraft would appear to depend on current fashion rather than on good ergonomics reasons. Strip displays are certainly more difficult to read than conventional dial and pointer instruments, especially under the vibration conditions to be found in helicopters. One can always detect the approximate angular position of a pointer on a circular dial, no matter how blurred it might appear due to vibration. The pointer's position on a strip instrument is far harder to sense, and usually will have to be very carefully read since it is more difficult to detect linear movements and positions than angular ones. This is particularly so if low frequency vibration (ie, 1-30 Hz) is present. Vibration blurred scales and pointers on a strip display can form nodal images which are difficult to relate to one another. An argument often put forward in favour of strip displays is that if used, for example, in multi-engined aircraft to show engine speed under normal operating conditions, the vertically mounted strips can be scanned along, and any
Fig. 5
Sptifire Mk I cockpit of 1939, with the 'Basic Six' blind flying panel
deviation from the norm on one engine can be detected immediately. This form of scanning for faults, has, of course, been used in cockpits for many years with circular dial and pointer instruments, by rotating the instruments in their mounting until the pointers are horizontal at the 3 o'clock position for normal operating conditions. As one leading instrument manufacturer states, (Anon, 1976) "Although the vertical tape instrument has some advantages over the circular scale instrument it sometimes presents a problem when allocating panel space because of its awkward shape as well as presenting an ergonomic problem when used in serried ranks; when the pilot might not always be able to sort out quickly which of the many vertical lines is the one with which he is immediately concerned." It is interesting to note that while the present generation of wide body American transport aircraft cockpits contain strip instruments, the cockpit mock-up of the future 'NASA/ Boeing terminal configured vehicle' contains only conventional circular scale instruments and two electronic or cathode ray tube (CRT) displays.
Applied Ergonomics
March 1977
25
Fig. 6
Fig. 7
Mosquito NF Mk 38, showing early use of CRTs and intrusion of systems into the cockpit, circa 1950
Systems and the exponential rise in the number of instruments The coming of the jet engine did not, in itself, radically change the number or type of cockpit instruments. Perhaps the greatest change, certainly as far as numbers of instruments and switches are concerned, was due to the new and advanced systems which began to appear towards the end of World War II. The Vampire jet aircraft's cockpit, shown in Fig. 6, differs little from that of the earlier Spitfire, but the night-fighter cockpit of Fig. 7 is really beginning to take on a different appearance with its early cathode ray tube display for radar. This cockpit shows the transition from the earlier generation, with its 'basic six' blind flying panel (centre left) and gas meter type dial (right), to the modern systems hardware of CRTs and rows of switches and contact breakers (upper right). Fig. 8 represents typical cockpit layout of the 1960s with almost all of the cockpit panel space taken up by instruments, lights and switches. In fact, some additional instruments, which intrude into the pilot's external vision
26
Vampire Mk 20 cockpit, little different in basic layout to the Spitfire a decade earlier
AppliedErgonomics March 1977
area, have been added above the cockpit combing. One reason for the massive increase in cockpit instruments and switches is that for the past decade or so, an aircraft type might have a useful working life of 20 years or more (eg, Hunter, Canberra, Phantom). During this time the aircraft's role might change from, say, a high altitude fighter to a low level strike aeroplane. The cockpit layout might have been optimised at the start for use as a fighter, but as the role has changed, so new systems have been added, which has required additional instrumentation to control and monitor them. This has led to very cluttered unergonomic cockpit layouts and an almost exponential rise in the number of instruments, as shown in Fig. 10. A single seat cockpit of the modern strike aircraft might contain over 300 instruments, indicators, controllers and switches (Shaw and Port, 1972; Fozard, 1969; Harlow, 1974). This rise in the number of systems (and therefore instruments to be monitored) has been accompanied by an increase in aircraft speed and performance (see Fig. 11). This increase in speed has served to aggravate the pilot's task. Now he not only has more instruments to monitor, but
The technology is now available in the form of CRT displays, to present only that information that is currently required. With a CRT display, the pilot will probably be given the basic flight information of airspeed, altitude, attitude, and heading (as normally displayed by the 'basic T' layout). He will then select other quantities such as engine parameters and check lists to be displayed, while system malfunctions could be programmed to be presented to him automatically. At present, aircrew often have to carry a bagful of manuals for route navigation, radio frequencies, check lists and emergency procedures with them to the aircraft. These sometimes present stowage problems in the cockpit. The suitably programmed CRT disply offers an elegant solution to this problem. Fig. 12 shows a typical pre-flight check list. Note that the operator has had to interact with the system as he works through the list. Dots have appeared against the first four items that he has checked. He now has to check 'probe heat' and if satisfied with it he will press the appropriate button and move on to the next check. If he misses the check the system will warn him of his error.
Fig. 8
Example of pilot's cockpit of an aeroplane in service today
In addition to these uses, the CRT display of basic flight information might be combined with the low light television view of the outside world for night operations, (see Fig. 13). This is alright as far as it goes, but has the disadvantage that the pilot has to look inside the cockpit at this head-down display with its limited field of view. He may have to time share between this display and the outside world.
less time in which to do so. It has been estimated that if the recent exponential rise in the number of cockpit instruments continues, by the 1980s cockpits will contain between 200 and 300 instruments. Fortunately, a solution is already at hand, in the form of multifunction CRT and other types of electronic displays.
Current and future cockpits There are many ways of saving panel space or reducing the number of instruments in the cockpit. Some methods are good, some are less than good, and even dangerous. For example, two- or three-pointer instruments are used. These instruments certainly save space, but sometimes at the cost of greater reading difficulty and increased errors. The fatal accidents which have been caused by misreading the threepointer altimeter are well-known examples of the results of poor display design. The modern single-pointer altimeter combined with a digital readout overcomes most of the problems associated with the three-pointer instrument, giving both precise height and rate of change of altitude information clearly and unmistakably.
Simple status indicators such as lights can sometimes be used to save space by replacing bulkier dials. Often the pilot or flight engineer needs only to know whether the system is within limits, which can be indicated by warning lights. He does not need to know the precise state of the system which requires a dial to indicate it. Even when he does need to know a precise value of the system that he is monitoring, he may need to check it only once or twice per flight. For the rest of the time the instrument is cluttering up the cockpit and possibly acting as a distraction to the pilot.
Fig. 9
Lynx helicopter cockpit, 1974, showing trial layout of strip and conventional circular instruments
Applied Ergonomics March 1977
27
-!
60~ 50 "u)
×
40-
/ X ~X
E
"6 Z
v×Af Jo
~ y /×x
1900 I0
20
~
40 50 Yeor
60
70
Fig. 10 Cockpit instrument growth. Fixed wing, single seat fighter t y p e aircraft
. . . . . . . . . . . . . . . . . . . . . .
200£
1800
•
-
•
•••
0~ =E 1200 ._c
The helmet mounted display (HMD) could be described as the ultimate development of the helmet mounted sight which itself comes mid-way between the HUD and HMD. The helmet mounted sight consists of a boresight with a limited amount of extra information added to it. The device is collimated and provides a simple display in front of the operator's eye. Figs. 15 and 16 show a typical helmet mounted sight and an example of the clear presentation that might be produced in front of one of the eyes of the pilot. It is designed to improve man's ability to aim weapons or sensors at potential targets by merely looking in the target's direction; sensors within the cockpit detect the
10£x3 E
o 800 ~E o
400
Despite the potential advantages of CRT displays, and other electronic displays such as LEDs (light emitting diodes), LCDs (liquid crystal displays), plasma panels, etc, there is the danger that their full value will not be realised. The tendency to try to put too much information on the display is strong and must be countered by good ergonomics guidance. Since man is effectively a single channel device, albeit one that time shares, there is little to be gained by trying to present him simultaneously with all of the information he needs throughout the entire flight. He can only process a relatively small amount of it at any instant, even when working at peak capacity. Under periods of extreme stress his processing rate may be even further reduced and a surfeit of signals will in no way help him to return to his previous higher processing rate. This excess of signal presentation is already occurring with some instruments such as HUDs, hehnet mounted sights and displays.
t600 1400 --
spent looking within the cockpit will reduce his chances o~ making a safe landing. Thus, a HUD can be of immense benefit in some, otherwise, marginal situations. In addition, the HUD has another advantage that its collimated image bestows. Since the image is presented at infinity, it is Less affected by vibration than conventional head-down instruments, as Fig. 14 so obviously shows. Despite its obvious advantages, the current HUDs have the serious shortcoming of an inadequate view. Only a small part of the outside world can be seen through the HUD 'porthole'. This results in HUD clutter which could be reduced if a larger field of view could be provided.
!
200 0
Fig. 11
1900 t0
20
30
40 Yeor
I 50
I 60
I 70
Maximum speed of single seat aircraft w i t h date of entry into service
Alternatively, information may be superimposed on the real world outside by using a head-up display (HUD). In this display the CRT image is projected onto a screen in front of the pilot and collimated, so that he sees the information 'outside' the cockpit at infinity. (See Fig. 14.) This enables him to maintain his view of the outside world without having to spend time to look 'head-down' and search for information from the conventional panel mounted instruments. The HUD is particularly useful when, for example, approaching a runway in fog where the pilot needs to keep his eyes skinned. In this situation, the pilot has little time to see and to recognise the runway and then to decide whether it is safe to attempt a landing. Any time
28
Applied Ergonomics
March 1977
Fig. 12
Typical check list, illustrating the versatility of the C R T display
Fig. 13 A possible CRT display format of basic flight ird~,ormation superimposed on a I'ow liigh.t TV view of the outside world
Fig. 14 Collimated Head-Up-Display image, illustrating clarity of information presentation in a vibrating environment
Fig. 15 A first generation Helmet Mounted Sight
Fig. 16 Pilot's eye view with Helmet Mounted Sight
Applied Ergonomics
March 1977
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The HMD is a far more complex device which produces a complete display in front of one eye of the pilot (see Fig. 17). leaving his other eye free to view the real world. Figs. 18 and 13 show the sort of images that might be presented on an HMD. It has been claimed that by presenting a collimated display directly in front of the eye, information can be displayed over a far greater area than can be done by HUDs or panel mounted instruments, whose area is limited by the need for windscreens and cockpit controls. While the HMD is potentially a most useful device, much of the design effort, so far, seems to have gone to maximising the amount of information displayed to the man. Few seemed to have questioned whether it is the correct information or how much of it a man can process. Unless these aspects receive the attention that they clearly deserve, the future pilot will be presented with more and more information which will be utilised by him less and less. The cost and complexity of his displays will increase and so will his workload, but the overall efficiency of the man-machine system will decline due to ergonomic shortcomings of the display interface.
Acknowledgements The author would like to thank Marconi Elliott Ltd and Smiths Industries Ltd for their permission to use their material for some of the text and illustrations in this paper.
Fig. 17 Second generation Helmet Mounted Display
© Copyright Controller HMSO, London, 1976.
References Anon 1976 Smiths Industries Aviation Review, Evolution of the instrument panel, 32, 19-20, 34, 14-16. Chorley, R. 1976 "70 years of flight instrument displays". The third HP Folland Memorial Lecture. Royal Aeronautical Society London. Coombs, L.F.E. 1972-74 Air Enthusiast, February, June and November 1972, pp 6 3 - 6 7 , 2 9 1 - 2 9 3 , 2 3 7 - 2 4 0 ; April and October t973 pp 1 8 8 - 1 9 1 , 1 7 2 - 1 7 6 ; a n d August 1974, pp 84-87. Front Office Evolution 1-6.
Fozard, J.W. Fig. 18 A typical pilot's eye view through a Helmet Mounted Display
position of the helmet and feed data to a computer which then calculates where the man is looking and finally programs the weapon system where to point. At present, the helmet mounted sights appear to present about the right quantity of data to the man. However, as the helmet sighting systems develop again, there will be the tendency to try to present more and more information around the sight. Eventually this will clutter up the display and reduce some of the sight's present advantages of clear presentation.
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AppliedErgonomics March 1977
1969 The Harrier. J.D. North Memorial Lecture, Royal Aeronautical Society, London. Hadow, P.G. 1974 A comparison of the number of cockpit displays and controls in 8 military helicopters. Unpublished RAE Report.
Rolfe, J.M. 1964 The fighter cockpit 1910-1963. RAF IAM Report No 222.
Shaw, M., and Port, W.G.A. 1972 A comparison of the number of cockpit displays and controls in 6 military aircraft. RAE Report TR 82140.