How Do you "Lock On" to an altitude with Glass Cockpit
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How Do you "Lock On" to an altitude with Glass Cockpit
OK, I'm the first to admit I'm a steam gage trained pilot with zero experience with glass cockpits.
In a steam gage cockpit, it was extremely easy to visually "lock on" to an altitude that you needed to maintain. When flying manually, you simply kept the big altimeter needle pointing in the same direction once you arrived at your assigned altitude (to the best of your ability). Small deviations above and below your assigned altitude are easily seen without actually looking at the gage, you only need to scan your eyes across and note the needle angle.
Glass cockpits of both A and B aircraft appear to involve a simulated rotating drum display similar to a car's mechanical odometer, except that the drums can rotate either direction. ( I've seen the moving "tape" display behind the altitude indication on the "bus in operation.)
What is not clear to me is what technique a pilot would use to "lock on" to an assigned altitude if they wished to manually fly the aircraft. If you are holding FL370, for example, on or a little above altitude reads 37030 perhaps,
a little low and it reads 36950, but you must actually look at the indication to read it, don't you? Is there a simple way to scan it without looking at it?
I'm wondering whether current PFD altitude displays make it difficult to maintain altitude awareness while flying manually.
In a steam gage cockpit, it was extremely easy to visually "lock on" to an altitude that you needed to maintain. When flying manually, you simply kept the big altimeter needle pointing in the same direction once you arrived at your assigned altitude (to the best of your ability). Small deviations above and below your assigned altitude are easily seen without actually looking at the gage, you only need to scan your eyes across and note the needle angle.
Glass cockpits of both A and B aircraft appear to involve a simulated rotating drum display similar to a car's mechanical odometer, except that the drums can rotate either direction. ( I've seen the moving "tape" display behind the altitude indication on the "bus in operation.)
What is not clear to me is what technique a pilot would use to "lock on" to an assigned altitude if they wished to manually fly the aircraft. If you are holding FL370, for example, on or a little above altitude reads 37030 perhaps,
a little low and it reads 36950, but you must actually look at the indication to read it, don't you? Is there a simple way to scan it without looking at it?
I'm wondering whether current PFD altitude displays make it difficult to maintain altitude awareness while flying manually.
Last edited by Machinbird; 27th May 2012 at 04:59. Reason: Add reference to the moving tape display
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It is just a new scan that you learn, same way it took you a while to learn your steam gauge scan.
You speak about locking the needle and being able to see small deviations, you still need to read the altitude (?) to see how big your deviation is and if you have corrected it.
Your just keeping the altimeter constant, not sure where you are getting confused?
You speak about locking the needle and being able to see small deviations, you still need to read the altitude (?) to see how big your deviation is and if you have corrected it.
Your just keeping the altimeter constant, not sure where you are getting confused?
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Gotta say that when I transitioned from the "Classic" to the "400" that I found it was (in the end) easier to maintain a more accurate altitude.
These days of course, the only places you can normally hand fly at 37,000 ft are in Afghanistan and Antarctica (on our company's routes).
The technique I tended to use (which is what you are searching for) was to keep the VSI pointer pointing at the Altimeter number you wanted.
hth.
N
These days of course, the only places you can normally hand fly at 37,000 ft are in Afghanistan and Antarctica (on our company's routes).
The technique I tended to use (which is what you are searching for) was to keep the VSI pointer pointing at the Altimeter number you wanted.
hth.
N
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Well, if I want to keep my altitude in an A320 during manual flight with FD off, I would indeed be monitoring the digital readout, but you could also look at the area I highlighted with an orange ellipse in the picture below.
You can see that the selected altitude in blue is slightly above the yellow reference line, so you know that your slightly low just by looking at that.
At FL370 in RVSM airspace, you would normally be flying on the autopilot of course, but there's nothing stopping the pilot from flying manually, FD off, during approach (unless you fly for some stupid company which doesn't allow their crew to do so)
You can see that the selected altitude in blue is slightly above the yellow reference line, so you know that your slightly low just by looking at that.
At FL370 in RVSM airspace, you would normally be flying on the autopilot of course, but there's nothing stopping the pilot from flying manually, FD off, during approach (unless you fly for some stupid company which doesn't allow their crew to do so)
Last edited by Cagedh; 27th May 2012 at 07:10.
I find it rather instinctive to "lock onto an altitude", without the need to actually read any numbers.
Just set the desired altitude in the FCU (MCP), and then keep the altitude symbol/bug (the big blue square) aligned together with the altitude indication box (yellow box).
If the blue square (altitude bug) rises above the yellow square (altitude indication), it means you are descending, so just pitch upwards.
If the blue square (altitude bug) moves downwards, it means you are climbing, so pitch downwards.
Just set the desired altitude in the FCU (MCP), and then keep the altitude symbol/bug (the big blue square) aligned together with the altitude indication box (yellow box).
If the blue square (altitude bug) rises above the yellow square (altitude indication), it means you are descending, so just pitch upwards.
If the blue square (altitude bug) moves downwards, it means you are climbing, so pitch downwards.
Last edited by John Citizen; 27th May 2012 at 11:17.
What a crappy-looking PFD. 
FWIW, machinbird, I do have more difficulty interpreting IAS and Altitude on a tape-PFD. No problem of course, but it is more difficult. The saviour is, as mentioned above, the big bug adjacent to the desired IAS or altitude target that helps you spot an error.
A needle approaching the six or twelve o'clock was more intuitive. No space on the square "dial" for that these days though! I always laugh when remember during my EFIS conversion, the CBT man saying that the PFD was in the classic T instrument layout. Ha!
FWIW, machinbird, I do have more difficulty interpreting IAS and Altitude on a tape-PFD. No problem of course, but it is more difficult. The saviour is, as mentioned above, the big bug adjacent to the desired IAS or altitude target that helps you spot an error.
A needle approaching the six or twelve o'clock was more intuitive. No space on the square "dial" for that these days though! I always laugh when remember during my EFIS conversion, the CBT man saying that the PFD was in the classic T instrument layout. Ha!
Perhaps many pilots have difficulty with raw instrument flying when using glass display formats.
A short, limited history of the development of ‘glass’ instruments (including LCD, LED, etc) indicate that there have been many weaknesses with tape formats in comparison with conventional dial instruments. The reappearance of dial formats on the larger ‘glass’ displays perhaps reinforce this point.
Instrument formats with glass were initially constrained by the size of the equipment and computing power. A simple ‘look-alike’ attitude display provided an easier certification route for an untested technology. There were also parallel needs in computation for reliability and avoidance of ‘hazardous / misleading’ information; techniques such as dual-dissimilar hardware and software were used. This latter area and display media have progressed rapidly in the last 20 yrs.
Wider displays enabled a tape format for airspeed; there was significant debate about the direction of the numbers, but the increased use of FD/autopilot/throttle was argued to balance any ‘human factors’ concerns (speed/pitch/control convention). Note that those aircraft which initially did not have autothrottle chose an alternative orientation – Gulfstream high numbers down; IIRC many manufacturers gave operators the choice, but none strayed from the norm.
Automation may hide these weaknesses, but they are still there; try a non-autothrottle, non FD night/IMC takeoff (as per the MEL), with an engine failure +- V2.
Research evaluated alternative formats; a nonlinear scale to give a wider view of the speed range, a curved scale to aid rate (acceleration) information, but none were really convincing.
The mandated Vmo/Mmo markings were supplemented with AOA computation to improved low speed awareness as did a range of bugs for ‘command’ or temporary limit speeds. A trend vector was added to aid acceleration (a crutch), and there were suggestions that it could be used as a ‘director’. Some formats might still be used in this way in lieu of AT. There were also issues about the direction of acceleration in a stall with trend vectors using an airspeed/inertial mix – aircraft speed decelerating but with inertial acceleration Earthwards! (cf AF447)
Many of these basic deficiencies are seen in early altimeter formats which became available with the larger (square) displays. Research again focused on dial formats including ‘egg’ shapes to improve the much deficient rate information deemed important in acquiring and maintaining altitude (“ … difficult to maintain altitude awareness while flying manually.”).
Note that glass VS (alt rate) formats also suffered; some VS formats change the indicator’s point of rotation at high VS to accentuate the value, they also use numerals and colour change to supplement the reduced analogue cues.
The key features in the difference between tape and dial formats are the lack of angular awareness of a moving pointer (including high speed = high, etc), the reduced length of the display scale, the swept area (dial airspeed, MD 80 anyone?).
Altitude formats need a counter pointer system; this required some of the new computation techniques such as dynamic widowing – larger displays and more computing power = cost, thus initially a compromise.
The altitude deficiencies have been slowly eroded with ‘crutches’, such as the shape of the ‘set bug’, with chevron/diagonal structures which aid detection of small movements, differing size of tape scale markings and colouring, and additional bugs (and even an alt trend vector?).
These appear to have improved the general performance of the displays to meet the industry’s requirements for monitoring automated flight.
However for manual flight, together with reducing experience in raw instrument flying, and perhaps without specific instrument flight training on tape displays (weaknesses in alt / attitude / speed scan), the height-keeping accuracy may be degraded, or at least a more demanding task which increases workload.
A short, limited history of the development of ‘glass’ instruments (including LCD, LED, etc) indicate that there have been many weaknesses with tape formats in comparison with conventional dial instruments. The reappearance of dial formats on the larger ‘glass’ displays perhaps reinforce this point.
Instrument formats with glass were initially constrained by the size of the equipment and computing power. A simple ‘look-alike’ attitude display provided an easier certification route for an untested technology. There were also parallel needs in computation for reliability and avoidance of ‘hazardous / misleading’ information; techniques such as dual-dissimilar hardware and software were used. This latter area and display media have progressed rapidly in the last 20 yrs.
Wider displays enabled a tape format for airspeed; there was significant debate about the direction of the numbers, but the increased use of FD/autopilot/throttle was argued to balance any ‘human factors’ concerns (speed/pitch/control convention). Note that those aircraft which initially did not have autothrottle chose an alternative orientation – Gulfstream high numbers down; IIRC many manufacturers gave operators the choice, but none strayed from the norm.
Automation may hide these weaknesses, but they are still there; try a non-autothrottle, non FD night/IMC takeoff (as per the MEL), with an engine failure +- V2.
Research evaluated alternative formats; a nonlinear scale to give a wider view of the speed range, a curved scale to aid rate (acceleration) information, but none were really convincing.
The mandated Vmo/Mmo markings were supplemented with AOA computation to improved low speed awareness as did a range of bugs for ‘command’ or temporary limit speeds. A trend vector was added to aid acceleration (a crutch), and there were suggestions that it could be used as a ‘director’. Some formats might still be used in this way in lieu of AT. There were also issues about the direction of acceleration in a stall with trend vectors using an airspeed/inertial mix – aircraft speed decelerating but with inertial acceleration Earthwards! (cf AF447)
Many of these basic deficiencies are seen in early altimeter formats which became available with the larger (square) displays. Research again focused on dial formats including ‘egg’ shapes to improve the much deficient rate information deemed important in acquiring and maintaining altitude (“ … difficult to maintain altitude awareness while flying manually.”).
Note that glass VS (alt rate) formats also suffered; some VS formats change the indicator’s point of rotation at high VS to accentuate the value, they also use numerals and colour change to supplement the reduced analogue cues.
The key features in the difference between tape and dial formats are the lack of angular awareness of a moving pointer (including high speed = high, etc), the reduced length of the display scale, the swept area (dial airspeed, MD 80 anyone?).
Altitude formats need a counter pointer system; this required some of the new computation techniques such as dynamic widowing – larger displays and more computing power = cost, thus initially a compromise.
The altitude deficiencies have been slowly eroded with ‘crutches’, such as the shape of the ‘set bug’, with chevron/diagonal structures which aid detection of small movements, differing size of tape scale markings and colouring, and additional bugs (and even an alt trend vector?).
These appear to have improved the general performance of the displays to meet the industry’s requirements for monitoring automated flight.
However for manual flight, together with reducing experience in raw instrument flying, and perhaps without specific instrument flight training on tape displays (weaknesses in alt / attitude / speed scan), the height-keeping accuracy may be degraded, or at least a more demanding task which increases workload.
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Not that I have flown that much "lock on" with A/P and F/D offs. But if I compare it with flying a raw data ILS I would use the high resolution of the PFD to my benefit. I try to find a very exact attitude that results in maintaining altitude. I mean for instance "the top of the airplane symbol has a small margin to the bottom of the 2,5 degree pitch line on the PFD". From there, working with very small changes of yoke pressure / attitude changes. This of course does not relieve me from scanning the altitude tape/VSI, but I can always go back and "rest" my eyes on the PFD knowing what attitude I am looking for. Harder in bumpy air.
Last edited by 172_driver; 27th May 2012 at 15:15.
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Wow. A lot of good inputs
. A big thank you for your answers. The key secret of easy altitude maintenance appears to be the 'bug' on the tape and its relationship to the altitude window. Special thanks to alf5071h from one 'prune' to another for the historical/developmental perspective (hint: look at his bio). I'm going to have to look at some of the other techniques mentioned.
Lightning Mate. Been there, done that. The best save I ever made was when the target altitude didn't look right and I didn't pull the trigger.
I asked the question because I was wondering about a couple of AF situations wherein the crews were slow in recognizing they had left the assigned altitude.
Once you are >500 feet off, the bug is no longer visible and the scrolling altitude tape & rolling numbers didn't trigger a mental alarm bell for them.
When you have been cruising along for hours and the AP suddenly kicks off, it must be interesting getting your scan going, particularly at night in turbulent conditions.
. A big thank you for your answers. The key secret of easy altitude maintenance appears to be the 'bug' on the tape and its relationship to the altitude window. Special thanks to alf5071h from one 'prune' to another for the historical/developmental perspective (hint: look at his bio). I'm going to have to look at some of the other techniques mentioned.Lightning Mate. Been there, done that.
The best save I ever made was when the target altitude didn't look right and I didn't pull the trigger.I asked the question because I was wondering about a couple of AF situations wherein the crews were slow in recognizing they had left the assigned altitude.
Once you are >500 feet off, the bug is no longer visible and the scrolling altitude tape & rolling numbers didn't trigger a mental alarm bell for them.
When you have been cruising along for hours and the AP suddenly kicks off, it must be interesting getting your scan going, particularly at night in turbulent conditions.
Last edited by Machinbird; 27th May 2012 at 16:41.
This reminds me. When I first transitioned to glass (PA46-500TP), the instructor told me that my scan was about to become a stare. He was right.
On the other hand I have frequently watched those starting with the flight director on for take off (which is normal procedure during type rating) having great trouble trying to pin the needles together. They chase the needles and because of their intense concentration on pinning both needles into the miniature square their instrument scan is lost as is their situational awareness for a short period of time.
In the old days, pilots under training were criticised for chasing the ILS needles rather than pick a heading to keep on the ILS. Yet nowadays during engine failure after take off the pilot is exhorted to concentrate and FLY the needles of the flight director. No wonder some have continued difficulty using flight director indications during one engine inop climb out. In fact some pilots get seriously spooked while chasing the FD needles and it doesn't work out for them.
The instructional trick is to switch the FD off for initial engine out after take off training and once the pilot has that beaten then introduce the FD.
Mach, the recent incidents / accidents (AF447) might be a problem of general awareness due to weaknesses in instrument scanning – training and currency. In addition, with multiple ADC failures the pressure error correction to the altimeter may be removed and thus there is an apparent jump in the display which could encourage an overreaction. Also, possible bias from the dominating need for accurate height keeping in normal operations; thus crew’s not being familiar with the need to change thinking / behaviour patterns between normal and abnormal normal operations.
OK465, IIRC most of the US designed mechanical tapes were mounted vertical, whereas the UK Lightning had a combined Mach / Airspeed tape orientated left to right (high numbers right). Lightning Mate may have flown this version, but I don’t recall teaching him about missile launches (the other side of the hangar and ‘at camp’).
Although HUDs use similar formats and scales to those in EFIS, they may have different characteristics. A HUD ‘real world’ conformal display may not have the same characteristics as the FD overlaying ADI attitude. The pitch scaling can differ by as much as 5:1, perhaps modifying the perception of pitch rate between HUD and an ADI.
Any training for new technology requires modified techniques; Centaurus gives a good example with the FD, but I suspect that tape altimeters, HUD, etc, also require some ‘tricks’ in training.
A potential problem is that the industry accepts many aspects of normal operation of new systems without sufficient thought of abnormal ops where seeming minor differences can have significant effects on workload and situation awareness. Unfortunately these may only surface in incidents or accidents.
OK465, IIRC most of the US designed mechanical tapes were mounted vertical, whereas the UK Lightning had a combined Mach / Airspeed tape orientated left to right (high numbers right). Lightning Mate may have flown this version, but I don’t recall teaching him about missile launches (the other side of the hangar and ‘at camp’).
Although HUDs use similar formats and scales to those in EFIS, they may have different characteristics. A HUD ‘real world’ conformal display may not have the same characteristics as the FD overlaying ADI attitude. The pitch scaling can differ by as much as 5:1, perhaps modifying the perception of pitch rate between HUD and an ADI.
Any training for new technology requires modified techniques; Centaurus gives a good example with the FD, but I suspect that tape altimeters, HUD, etc, also require some ‘tricks’ in training.
A potential problem is that the industry accepts many aspects of normal operation of new systems without sufficient thought of abnormal ops where seeming minor differences can have significant effects on workload and situation awareness. Unfortunately these may only surface in incidents or accidents.
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Originally Posted by alf5071h
Mach, the recent incidents / accidents (AF447) might be a problem of general awareness due to weaknesses in instrument scanning – training and currency. In addition, with multiple ADC failures the pressure error correction to the altimeter may be removed and thus there is an apparent jump in the display which could encourage an overreaction. Also, possible bias from the dominating need for accurate height keeping in normal operations; thus crew’s not being familiar with the need to change thinking / behaviour patterns between normal and abnormal normal operations.
Throw in the surprise factor, mental overload, adverse Circadian rhythms, night, turbulence and a different flight control law such as the half fish, half fowl, Alt2(b) law and a rusty pilot will be in a world of difficulty getting any scan going.
IMHO pilots are going to have to fly more to maintain handling skills, or else AF447 may well mark the reaching of the tipping point where handling skills can no longer be trusted to save the day. The RVSM airspace reason for not hand flying must be overcome. Think of the training opportunities going to waste!
Can anyone think of a reason why this won't work? (I believe the institutional problems can be overcome.)
Originally Posted by Machinbird-AF447 Thread No 8
Let us think outside the box for a moment. Supposing we added in a manual flying training mode into our aircraft.
How did you learn to hold altitude? When you began to get a little off altitude, didn't your instructor cluck at you and if you continued to diverge, didn't he give the stick a nudge to put you back in the tolerance band. Why couldn't our aircraft with their sophisticated autopilots do something similar? No need to breech RVSM limits yet we can still get actual handling time and build a scan. Any pilot worth his salt hates having the stick nudged. When you get tired, you can let OTTO have the complete aircraft. Think of the potential to actually monitor a pilot's handling skill and to automatically record actual handling time! True, you won't get as much time to balance your checkbook or to read a magazine, but remember why you are sitting in the front seats!
How did you learn to hold altitude? When you began to get a little off altitude, didn't your instructor cluck at you and if you continued to diverge, didn't he give the stick a nudge to put you back in the tolerance band. Why couldn't our aircraft with their sophisticated autopilots do something similar? No need to breech RVSM limits yet we can still get actual handling time and build a scan. Any pilot worth his salt hates having the stick nudged. When you get tired, you can let OTTO have the complete aircraft. Think of the potential to actually monitor a pilot's handling skill and to automatically record actual handling time! True, you won't get as much time to balance your checkbook or to read a magazine, but remember why you are sitting in the front seats!
Mach, I disagree with the majority of the arguments calling for greater focus on manual flying skills; not just the view in #17.
Recent accidents indicate that the human problems were predominantly due to the choice of action, and not that the crew couldn’t fly the aircraft. In many cases the aircraft was flown (accurately) into the wrong part of the flight envelope. I exclude AF447 because there may be other system and trim issues, and we don’t have all of the details yet.
Choice of action requires good situation awareness. With inaccurate situation assessment, then flight control inputs for a chosen action might be hesitant, or exploratory – getting a feel for the situation. The resultant aircraft motion may not match the predictions from the pilot’s understanding.
With good situation assessment, choosing an appropriate action should result in a high probability of success even if the flying is not particularly accurate. Furthermore this action should change the situation to something which was expected, thus confirming the choice – thus a need to continuously reassess the situation.
Training for this should also involve how to combat surprise and 'getting back into the loop'; changing from passive monitoring (automation) to active awareness and control (manual).
Flight instruments provide a major contribution to awareness. A danger with modern displays is that single cue or automatic flight may result in an expectation of ‘single-source’ recovery in abnormal conditions (instant answer).
Good instrument flying skill (awareness) involves scanning a range of instruments, and the construction a time based model of what has happened, what is happening, and what might happen; past, present, future. These snapshots are combined with previous knowledge to provide a mental model – the situation.
Whilst modern displays provide very good inputs to this process for navigation (includes time), it might be questionable if the aircraft handling parameters (speed, attitude, altitude) are as good as conventional ‘dial’ instruments. In particular, note the weaknesses in rate information, this is a critical timeline input to the mental model.
Poor situation awareness due to these aspects may also result in poor timing of the control inputs – sharp / harsh movements – getting the feel for or generating a new understanding of the situation as much as for the aircraft response. This might be interpreted as poor flying skills, but the cause is elsewhere.
Recent accidents indicate that the human problems were predominantly due to the choice of action, and not that the crew couldn’t fly the aircraft. In many cases the aircraft was flown (accurately) into the wrong part of the flight envelope. I exclude AF447 because there may be other system and trim issues, and we don’t have all of the details yet.
Choice of action requires good situation awareness. With inaccurate situation assessment, then flight control inputs for a chosen action might be hesitant, or exploratory – getting a feel for the situation. The resultant aircraft motion may not match the predictions from the pilot’s understanding.
With good situation assessment, choosing an appropriate action should result in a high probability of success even if the flying is not particularly accurate. Furthermore this action should change the situation to something which was expected, thus confirming the choice – thus a need to continuously reassess the situation.
Training for this should also involve how to combat surprise and 'getting back into the loop'; changing from passive monitoring (automation) to active awareness and control (manual).
Flight instruments provide a major contribution to awareness. A danger with modern displays is that single cue or automatic flight may result in an expectation of ‘single-source’ recovery in abnormal conditions (instant answer).
Good instrument flying skill (awareness) involves scanning a range of instruments, and the construction a time based model of what has happened, what is happening, and what might happen; past, present, future. These snapshots are combined with previous knowledge to provide a mental model – the situation.
Whilst modern displays provide very good inputs to this process for navigation (includes time), it might be questionable if the aircraft handling parameters (speed, attitude, altitude) are as good as conventional ‘dial’ instruments. In particular, note the weaknesses in rate information, this is a critical timeline input to the mental model.
Poor situation awareness due to these aspects may also result in poor timing of the control inputs – sharp / harsh movements – getting the feel for or generating a new understanding of the situation as much as for the aircraft response. This might be interpreted as poor flying skills, but the cause is elsewhere.
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Initial transition to tapes from round dials does present some instrument scan issues. I was surprised at the difference in effort. Our transition sim had us fly a handflown level off at 2000' immediately after takeoff. Simple... except everyone overspeed 250 kts because they were struggling with their scan transisitioning to the tape altimeter/VSI.
Looking at the altimeter and VSI you can instantly see the altimeter needle pointing straight up and the VSI needle at 9 o'clock and you KNOW you're at a thousand foot with zero sink. It's not that obvious on tapes, especially when transitioning from years of round dial flying. You adjust and it becomes much easier. It eventually becomes second nature, just like round dials.
Looking at the altimeter and VSI you can instantly see the altimeter needle pointing straight up and the VSI needle at 9 o'clock and you KNOW you're at a thousand foot with zero sink. It's not that obvious on tapes, especially when transitioning from years of round dial flying. You adjust and it becomes much easier. It eventually becomes second nature, just like round dials.