B737 No Uptrim during Cat III
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B737 No Uptrim during Cat III
I was given a no uptrim (no automatic pitch trim wheel input) at 400ft during an autoland approach in Cat III.
I decided to continue, as this is only a backup feature in case the autopilots should disconnect and you are sleeping and don't flare or goaround by yourself...
But somebody is of a different opinion...
I decided to continue, as this is only a backup feature in case the autopilots should disconnect and you are sleeping and don't flare or goaround by yourself...
But somebody is of a different opinion...
Last edited by LEM; 11th Jan 2005 at 17:19.
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I assume you are talking 737. I was under the impression that the trim was needed for the autoland to flare correctly. For the last 400' the autopilot holds considerable elevator forward pressure against the trim, and just releases the pressure furing the flare commencing at 50'. I suspect you could expect a very hard landing without the trim being there.
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So maybee the question is,
Is it ok to let the AP to excert considerable force on the controls against the nose up trim, or is it ok for the AP to exert considerable force on the controls during the flare?
I can see the point though which seems to be, during the flare when the aircraft is most likely to be bent, if the AP has trimmed up, there will be little force on the controls, so the AP is better able to control the A/C with more control (evelator) authority in BOTH directions. If it doesnt trim up, during the flare, the evelator will be at or near the back stop (FL40 landings), making the flare dangerous when RETARD activates (power pitch down) or a GA very slow to commmence until the power comes on (pitch up power).
Hope that helps,
Mr L.
Is it ok to let the AP to excert considerable force on the controls against the nose up trim, or is it ok for the AP to exert considerable force on the controls during the flare?
I can see the point though which seems to be, during the flare when the aircraft is most likely to be bent, if the AP has trimmed up, there will be little force on the controls, so the AP is better able to control the A/C with more control (evelator) authority in BOTH directions. If it doesnt trim up, during the flare, the evelator will be at or near the back stop (FL40 landings), making the flare dangerous when RETARD activates (power pitch down) or a GA very slow to commmence until the power comes on (pitch up power).
Hope that helps,
Mr L.
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I may be about to be corrected on this, but the nose up trim is not necessary to make an autoland happen but is probably required in certain circumstances (since there seems to be a secondary debate here about whether it is fundamentally required for an autoland or not).
As far as I'm aware it only occurs when an aircraft is fail passive. On the 757 for example, with all 3 autopilots engaged and when the aircraft is 'LAND 3' the nose up trim does not occur, presumably because the aircraft is fail operational and a single failure will not have a detrimental effect on the autoland itself. However, it does trim nose up when it is 'LAND 2' and a single failure would be more troublesome.
I don't know much about the 737 but with 2 autopilots I presume that it would always need to trim nose up at the relevant point in case of a single failure.
As far as I'm aware it only occurs when an aircraft is fail passive. On the 757 for example, with all 3 autopilots engaged and when the aircraft is 'LAND 3' the nose up trim does not occur, presumably because the aircraft is fail operational and a single failure will not have a detrimental effect on the autoland itself. However, it does trim nose up when it is 'LAND 2' and a single failure would be more troublesome.
I don't know much about the 737 but with 2 autopilots I presume that it would always need to trim nose up at the relevant point in case of a single failure.
From the Boeing volume 2, NG
400 Feet Radio Altitude
"The stabilizer is automatically trimmed an additional amount nose up. If the A/P`s subsequently disengage, forward control column force may be required to hold the desired pitch attitude.
If FLARE is not armed by approximately 350 feet RA, both A/Ps automatically disengage."
400 Feet Radio Altitude
"The stabilizer is automatically trimmed an additional amount nose up. If the A/P`s subsequently disengage, forward control column force may be required to hold the desired pitch attitude.
If FLARE is not armed by approximately 350 feet RA, both A/Ps automatically disengage."
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I would consider the absence of the nose-up-trim a flight guidance failure. (if I would notice it, that is
)
Any flight guidance failure during a CAT3 approach requires a go around. It is a fail passive procedure, anyway.
)Any flight guidance failure during a CAT3 approach requires a go around. It is a fail passive procedure, anyway.
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On the 757 for example, with all 3 autopilots engaged and when the aircraft is 'LAND 3' the nose up trim does not occur, presumably because the aircraft is fail operational and a single failure will not have a detrimental effect on the autoland itself. However, it does trim nose up when it is 'LAND 2' and a single failure would be more troublesome.
The uptrim is just a precaution in case of AP disengagement.
As long as you are awake and ready to flare manually, why not continue?
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That is true LEM, but (I know, there's alway a but) I thought the point of LVP ops was that the pilot did not have enough visual cues to land the aircraft??
In CAT III A/B/C there is little or NO visual cues available until it is too late to effect a correction to a deviation to the desired flight path. You either land if happy or G/A. So a manual flare is out of the question???? This would suggest that the pitch mode is disconnected before completion of the "AUTO" land, and is hence not a auto land, but a CAT II/I approach to minimums with a manually flown segment.
Sorry for all the q's, there was 6 instead of 60 knots at work today-I have lost all sense of normality...........
Mr L.
In CAT III A/B/C there is little or NO visual cues available until it is too late to effect a correction to a deviation to the desired flight path. You either land if happy or G/A. So a manual flare is out of the question???? This would suggest that the pitch mode is disconnected before completion of the "AUTO" land, and is hence not a auto land, but a CAT II/I approach to minimums with a manually flown segment.
Sorry for all the q's, there was 6 instead of 60 knots at work today-I have lost all sense of normality...........
Mr L.
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Hi, Mr Levitator, when I say "Why not continue?" I don't mean you necessarily want to absolutely land.
Example:
A) AP disconnects at 80 ft: you still have plenty of time to go around manually.
B) AP disconnects at 50 ft: you see and decide to land. Still plenty of time to flare manually.
C) AP disconnects at 20 ft: that means the airplane has already started to flare. You instinctively pull a little bit aft and the landing is made.
Or, you can still go around, maybe contacting the runway, but that's no big deal.
And I raise one more point: if the uptrim is so important, why don't we have a call like "Uptrim checked" at, say, 300ft?
Most people won't even notice the uptrim hasn't taken place, without a call.
Last, yesterday we did an autoland, lightweight, and that was quite rough! I could have landed better when drunk!
More thoughts?
Thank you, LEM.
Example:
A) AP disconnects at 80 ft: you still have plenty of time to go around manually.
B) AP disconnects at 50 ft: you see and decide to land. Still plenty of time to flare manually.
C) AP disconnects at 20 ft: that means the airplane has already started to flare. You instinctively pull a little bit aft and the landing is made.
Or, you can still go around, maybe contacting the runway, but that's no big deal.
And I raise one more point: if the uptrim is so important, why don't we have a call like "Uptrim checked" at, say, 300ft?
Most people won't even notice the uptrim hasn't taken place, without a call.
Last, yesterday we did an autoland, lightweight, and that was quite rough! I could have landed better when drunk!
More thoughts?
Thank you, LEM.
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Thats true but in real "on minima's" CAT III approaches I simply can't see (excuse the pun) how it is possible to see enough RVR to gain things like depth perception and textural flow rates....
The rough landing-I also did a CAT III yesterday-I agree with you entirley LEM. Sounds like the way Boeing (and Girls) likes it, Firm and in the right place!!
Mr L
The rough landing-I also did a CAT III yesterday-I agree with you entirley LEM. Sounds like the way Boeing (and Girls) likes it, Firm and in the right place!!
Mr L
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I don't know about the real aircraft but the 737 Classic simulator will execute a perfectly respectable smooth coupled landing just on one autopilot. Under this one autopilot operation there is definately no autotrim back at 400RA though, nor at any other stage. It is comforting to have that fall back availibility on one autopilot if you do not have a second autopilot available for some reason and you just have to get in in bad weather on the ILS.
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Hudson I am glad you mentioned that because the same thought struck me. We were told that Mr Boeing had to allow for the case where a crew for whatever reason did an approach with only one a/p engaged. (200/300/400 series)
It obviously has to stay in until cat one decision height but what then? either drop out or continue and land or fly stright into the ground, so the default was it would continue for A/land but it wasn't approved and therefore not published nor documented.
As you say there is no guarantee that the sim and the real beast will behave the same, and we couldn't of course try it on the real thing, so it became one of those urban myths which no-one is quite sure about.
Perhaps someone can clear this up?
It obviously has to stay in until cat one decision height but what then? either drop out or continue and land or fly stright into the ground, so the default was it would continue for A/land but it wasn't approved and therefore not published nor documented.
As you say there is no guarantee that the sim and the real beast will behave the same, and we couldn't of course try it on the real thing, so it became one of those urban myths which no-one is quite sure about.
Perhaps someone can clear this up?
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Intersting points, make sense, and comforting to know!
That seems to validate my original thought: there's no need for uptrim for the autopilot to land.
Re: depth perception and textural flow rates....
Just don't watch outside, so you won't be scared
Jokes apart, I'm half serious when I say that: the secret for landing without adequate visual cues (like in heavy rain with s*** wipers) is doing nothing. Just maintain constant parameters, disregarding your desire for visual certeinties, as following your senses will only screw up everything.
At around 20 ft, pull slightly and retard. That's it!
The challenge is resisting your instincts, but with experience that's quite easy - and rewarding. In the worst case, your landing will not be one your smoothest.
That seems to validate my original thought: there's no need for uptrim for the autopilot to land.
Re: depth perception and textural flow rates....
Just don't watch outside, so you won't be scared
Jokes apart, I'm half serious when I say that: the secret for landing without adequate visual cues (like in heavy rain with s*** wipers) is doing nothing. Just maintain constant parameters, disregarding your desire for visual certeinties, as following your senses will only screw up everything.
At around 20 ft, pull slightly and retard. That's it!
The challenge is resisting your instincts, but with experience that's quite easy - and rewarding. In the worst case, your landing will not be one your smoothest.
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You all gotta be kidding me!
We`re talking about an approach here with 200 meters RVR, and you`re talking about how to do a landing and that Mr Boeing is talking a lot of rubbish with this sissy uptrim. (slightly exagerating here
)
This is a dangerous way to go!
Surprise! You`re already screwing up everything, if you`re not going around without adequate visual cues! Know what the word adequate means?
Seriously, I made an actual cat3 approach in CDG yesterdaymorning, with 275 meters RVR A. It is really not a good plan to try that manually. Sure, if you have no other options left it might (just) be possible.
Stick to the procedure here, guys. You`re flying without outside reference at 50 feet height with 180 people in the back.
Do it safely, or don`t do it.
0A
We`re talking about an approach here with 200 meters RVR, and you`re talking about how to do a landing and that Mr Boeing is talking a lot of rubbish with this sissy uptrim. (slightly exagerating here
)This is a dangerous way to go!
the secret for landing without adequate visual cues (like in heavy rain with s*** wipers) is doing nothing. Just maintain constant parameters, disregarding your desire for visual certeinties, as following your senses will only screw up everything.
Seriously, I made an actual cat3 approach in CDG yesterdaymorning, with 275 meters RVR A. It is really not a good plan to try that manually. Sure, if you have no other options left it might (just) be possible.
Stick to the procedure here, guys. You`re flying without outside reference at 50 feet height with 180 people in the back.
Do it safely, or don`t do it.
0A
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Thanks for your input Seat 0A! Now that we have established that we must adheare to published regs and "Do it safely, or don`t do it", its back to original thread . What is your opinion Seat OA???? Is sissy up trim required?? What is its purpose?? And what do you think you might do if just after decision the AP disengaged??
Mr L.
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I'm not kidding at all, seat 0A, but maybe the way I expressed myself made you get me wrong.
It seems you took my posts as an encouragement to land below minima, or with no adequate visual cues.
That's really not the case.
In saying "the secret for landing without adequate visual cues (like in heavy rain with s*** wipers)" I meant "without the usual good cues".
Anyway, my original question was: is it really necessary to have an uptrim for an autoland, or is it just a certification precaution for a fail passive equipment?
Don't get me wrong: I'm not saying we should routinely land manually with 200mtrs RVR.
We are supposed to use autoland.
Fine.
What I'm saying is, in the remote case the autopilot should disconnect after your decision to land, i.e. after 50 ft, there's no problem in handling it manually, either completing the landing, either initiating a go-around.
In case you feel comfortable in completing the landing, this will probably be due to your experience, leading you to do the exact thing, i.e. nothing, and a very little correction just before touchdown.
Most inxperienced pilots tend to be disoriented in poor visibility, and to overreact needlessly.
That's human.
Yes I do. In my book, in order to make the decision to land, you must see three longitudinal elements, including one lateral.
That's it.
You know what that means?
Just three tiny lights, and a TDZ barrette.
That's adequate, according to the law, but sure the average driver would not feel very comfortable with such visual cues, at 300 kilometers per hour...
Hence my comments on the way the experienced and skilled pilot makes the difference.
Yes, my SOP say that if a malfunction occurs after the decision to land has been made, the Captain is entiteld to continue, if he determines this is the safest way to go.
LEM
It seems you took my posts as an encouragement to land below minima, or with no adequate visual cues.
That's really not the case.
In saying "the secret for landing without adequate visual cues (like in heavy rain with s*** wipers)" I meant "without the usual good cues".
Anyway, my original question was: is it really necessary to have an uptrim for an autoland, or is it just a certification precaution for a fail passive equipment?
Don't get me wrong: I'm not saying we should routinely land manually with 200mtrs RVR.
We are supposed to use autoland.
Fine.
What I'm saying is, in the remote case the autopilot should disconnect after your decision to land, i.e. after 50 ft, there's no problem in handling it manually, either completing the landing, either initiating a go-around.
In case you feel comfortable in completing the landing, this will probably be due to your experience, leading you to do the exact thing, i.e. nothing, and a very little correction just before touchdown.
Most inxperienced pilots tend to be disoriented in poor visibility, and to overreact needlessly.
That's human.
Know what the word adequate means?
That's it.
You know what that means?
Just three tiny lights, and a TDZ barrette.
That's adequate, according to the law, but sure the average driver would not feel very comfortable with such visual cues, at 300 kilometers per hour...
Hence my comments on the way the experienced and skilled pilot makes the difference.
Stick to the procedure here, guys.
LEM
Some of the posts in this thread show an appalling disregard for the principles of safety in our industry. If a manufacturer provides rules and guidance for operating an aircraft, then the crew must follow them; do not prejudge or assume that everything will be OK because … If you have been seeking a wind up, then you have achieved it.
I am not familiar with the 737 autopilot, but I do have extensive experience of similar systems, their certification, and Cat 3 operations. Up trim may provide assistance with the flare manoeuvre or with a go around if the autopilot disengages. More likely, it provides protection in the event of a failure. An autopilot certification requires the manufacturer to consider a hard nose down runaway failure and the more subtle slow-over failures, where the crew are unlikely to detect or alleviate the resultant hazardous flight path. Up trim is often used to mitigate the effects of these types of failure. Other failures involve the ILS ground station or other external effects including limiting terrain profiles.
Why in this forum do posters continually ignore the advice that some capabilities seen in simulators are not a basis for safe operations in the aircraft? Simulators are not real aircraft, they do not fly (or fail) like real aircraft; they are only an approximation suitable for gaining an appropriate level of knowledge, practicing procedures, and skills. Although aircraft are tested in extreme circumstances, few if any of the relevant parameters or conditions are in the simulator software.
No single strand system is certificated for operations in conditions that require dual path integrity. Operating limits, RVR etc have been chosen based on extensive research, and they provide the necessary safety margins for a safe operation (see below). Any one believing that these limits can be ignored or the associated procedures or techniques may be changed has little or no understanding of risk management and they are a hazard to him/herself and the industry in general.
More disconcerting are the attitudes shown by pilots claiming to be professionals. Even basic CRM should have taught the need for discipline and the control of macho and invulnerable (I can do anything) attitudes. In essence, you represent a single strand system, I hope that your airline crews you with very assertive first officers.
Ref the required visual references, there is the usual discontinuity in JARs between design and operating requirements. Note that design cert includes the need to assess position and flight path. An autopilot failure may have introduced a deviation; thus in order to make an assessment the crew probably requires seeing several longitudinal and lateral elements of the lighting system. The design regs also invoke pilot judgement re landing safely. This judgement is normally a comparison with experience of having flown the manoeuvre before, but of course this would have been done in the simulator, and … few simulations have an accurate visibility model for all conditions. Thus, the probability that a pilot has practiced a manual landing in the conditions encountered after an autopilot failure is low.
JAR-OPS 1 Subpart E
For Category IIIA operations, and for Category IIIB operations with fail-passive flight control systems, a pilot may not continue an approach below the decision height … unless a visual reference containing a segment of at least 3 consecutive lights being the centreline of the approach lights, or touchdown zone lights, or runway centreline lights, or runway edge lights, or a combination of these is attained and can be maintained.
JAR –AWO Subpart 3
Decision height is the wheel height above the runway elevation by which a go-around must be initiated unless adequate visual reference has been established and the aircraft position and approach path have been assessed as satisfactory to continue the approach and landing in safety.
I am not familiar with the 737 autopilot, but I do have extensive experience of similar systems, their certification, and Cat 3 operations. Up trim may provide assistance with the flare manoeuvre or with a go around if the autopilot disengages. More likely, it provides protection in the event of a failure. An autopilot certification requires the manufacturer to consider a hard nose down runaway failure and the more subtle slow-over failures, where the crew are unlikely to detect or alleviate the resultant hazardous flight path. Up trim is often used to mitigate the effects of these types of failure. Other failures involve the ILS ground station or other external effects including limiting terrain profiles.
Why in this forum do posters continually ignore the advice that some capabilities seen in simulators are not a basis for safe operations in the aircraft? Simulators are not real aircraft, they do not fly (or fail) like real aircraft; they are only an approximation suitable for gaining an appropriate level of knowledge, practicing procedures, and skills. Although aircraft are tested in extreme circumstances, few if any of the relevant parameters or conditions are in the simulator software.
No single strand system is certificated for operations in conditions that require dual path integrity. Operating limits, RVR etc have been chosen based on extensive research, and they provide the necessary safety margins for a safe operation (see below). Any one believing that these limits can be ignored or the associated procedures or techniques may be changed has little or no understanding of risk management and they are a hazard to him/herself and the industry in general.
More disconcerting are the attitudes shown by pilots claiming to be professionals. Even basic CRM should have taught the need for discipline and the control of macho and invulnerable (I can do anything) attitudes. In essence, you represent a single strand system, I hope that your airline crews you with very assertive first officers.
Ref the required visual references, there is the usual discontinuity in JARs between design and operating requirements. Note that design cert includes the need to assess position and flight path. An autopilot failure may have introduced a deviation; thus in order to make an assessment the crew probably requires seeing several longitudinal and lateral elements of the lighting system. The design regs also invoke pilot judgement re landing safely. This judgement is normally a comparison with experience of having flown the manoeuvre before, but of course this would have been done in the simulator, and … few simulations have an accurate visibility model for all conditions. Thus, the probability that a pilot has practiced a manual landing in the conditions encountered after an autopilot failure is low.
JAR-OPS 1 Subpart E
For Category IIIA operations, and for Category IIIB operations with fail-passive flight control systems, a pilot may not continue an approach below the decision height … unless a visual reference containing a segment of at least 3 consecutive lights being the centreline of the approach lights, or touchdown zone lights, or runway centreline lights, or runway edge lights, or a combination of these is attained and can be maintained.
JAR –AWO Subpart 3
Decision height is the wheel height above the runway elevation by which a go-around must be initiated unless adequate visual reference has been established and the aircraft position and approach path have been assessed as satisfactory to continue the approach and landing in safety.
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My thoughts go to the Go-Around. I was under the impression that the uptrim when making a Dual Channel app. is due to the fact that the AP is preparing for a G/A, before reaching minimums. In the event of a G/A with both AP's, they will stay in and the uptrim will ease the workload of the auto-trim when pitching up. It makes sense if you think about the single channel scenario; perfectly capable of flaring without uptrim but leaving the G/A for you to take care of - so no uptrim.
I suspect that if you would had made a G/A in your specific case where there were no uptrim, you would had gotten a steady read AP warning light telling you that the auto-trim wasn't following.... or at least possibly.
...or have I been misled?
I suspect that if you would had made a G/A in your specific case where there were no uptrim, you would had gotten a steady read AP warning light telling you that the auto-trim wasn't following.... or at least possibly.
...or have I been misled?
Last edited by CrossBars; 15th Jan 2005 at 21:59.