View Full Version : B737 No Uptrim during Cat III

11th Jan 2005, 18:01
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...

11th Jan 2005, 18:03
Which aircraft type?

The Greaser
11th Jan 2005, 18:07
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.

Mr Levitator
12th Jan 2005, 18:17
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.

12th Jan 2005, 22:31
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.

13th Jan 2005, 06:23
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."

seat 0A
13th Jan 2005, 08:39
I would consider the absence of the nose-up-trim a flight guidance failure. (if I would notice it, that is:ugh: )
Any flight guidance failure during a CAT3 approach requires a go around. It is a fail passive procedure, anyway.

13th Jan 2005, 17:14
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.

This seems to confirm my point, the autopilot doesn't really need the uptrim to take place to be able to flare.

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?

Mr Levitator
13th Jan 2005, 21:52
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.

14th Jan 2005, 07:51
Hi, Mr Levitator, when I say "Why not continue?" I don't mean you necessarily want to absolutely land.

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.

Mr Levitator
14th Jan 2005, 11:03
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

14th Jan 2005, 11:06
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.

14th Jan 2005, 11:24
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?

15th Jan 2005, 14:56
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.

seat 0A
15th Jan 2005, 15:15
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!
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.

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.


Mr Levitator
15th Jan 2005, 17:04
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.

15th Jan 2005, 17:20
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.
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?
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.

Stick to the procedure here, guys.
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.


The Greaser
15th Jan 2005, 17:35
I think you only need a lateral element of lighting for a cat II approach, not cat III.

15th Jan 2005, 20:52
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.

15th Jan 2005, 21:54
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?

Mr Levitator
16th Jan 2005, 08:45
If the AP was preparing for a GA, would it not trim Nose down to counter the pitch up when power was applied?? Next time you are in a sim, get to CAT I minima on 1 AP and press TOGA and don't touch the controls. The nose passes 20 degrees in about 3 seconds. Plus when the gear is selected up, that is a futher nose up trim change.

safetypee. Thanks for your post. Now that we have established you think we are lesser "pilots claiming to be professionals" its back to the original post.

What is your opinion???? If the AP disengages just after the decision to land, what would you do?? The thinking here is that runway contact is almost certain if a GA is executed. The result we are after is an A/C safely on the deck.

And do you continue if the Up Trim does not happen?? It could be a syptom of a latent problem about to manifest itself in the flare at <50ft in a RVR of 200m.......

A final note. There are now two threads which are designed to "set strait" the other posters on this thread. Why???? You don't even know who we really are, or what experience/positions we hold. I like to be able to discus the unusual, it often raises other questions. It is not as if we are going to try this in a real a/c. Discussion and debate is healthy, ie tech log on Pprune. So keep the posts sweet....

Mr L.

Right Way Up
16th Jan 2005, 10:01
If the auto trimming does not occur, does the Red Autopilot P/RST light not come on steady (disagreement between autopilot command and actual position). Thus an immediate go-around!
I remember taking the autopilot out at 60 ft on a practice autoland due to aircraft trying to snap left due intereference. The pressure required to land the aircraft in a safe attitude was surprising. Not something I would care to do in real Cat 3 wx.

seat 0A
16th Jan 2005, 10:05
safetypee, thank you for your comments. My thoughts exactly.

Mr. Levitator, discussing the unusual is quite something else then boasting about one`s abilities to take the aircraft outside the limits, as mr. LEM is advocating:
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.

He even goes as far as to say it is rewarding!

I seriously hope he will not go looking for more rewarding experiences.

Mr Levitator
16th Jan 2005, 11:56
If you are that concerned, PM LEM.

What are your thoughts regarding the trim????

B737 No Uptrim during Cat III is the thread title, what are your opinions on it????

For a bunch of pilots, there is not a lot of RTFQ here?!?!?!?!

Use PM or another thead for b##ching. I am sure if you PM LEM he will explain his point more clearly to you, and as his quote says, LEM was actually suggesting that making unnecessary control input are exactly what takes the a/c out of limmits!! Its kind of like flying a raw data ILS, the closer to decision, the smaller and more gentle the loc and g/s corrections have to be.

So a futher question. Why nose up trim?? If it were for a G/A, would it not be nose down, for the pitch power couple and the gear retraction??

Mr L

16th Jan 2005, 12:29
Mr. L - Yes that of course makes more sense. Have scanned through the manuals and can't really find any good explanation to this phenomenon :confused: Suspect that the engineers didn't really realize what a curious, kneed-to-know-every-little-detail, kind of people we are :D

On the other hand, how could one make the right decision if put in LEM's situation, without knowing its function and more importantly what to expect when it's not functioning? Both AP's still engaged, FLARE armed and everything seems fine. One could always see this as a non-normal operation of the AP system and do a G/A. Or, one could say that if this was a G/A situation shouldn’t the logic of the AP disconnect or give a warning?

When it comes to the steady red AP light below 800 feet RA and during app, it will come on if the Stab is out of trim. And in this case it was more in trim than had the normal 400 feet RA nose-up trim taken place.

Found one little note on the subject though that refer to the automatic G/A.
"The pitch mode cannot be changed from TOGA until sufficient nose-down trim has been input to allow single channel AP operation. This nose-down trim is automatically added by the AP to reset the trim input made by the AP at 400 feet RA and at 50 feet RA during the approach."
The AP is actually trimming the airplane out of the single channel operational range, which makes even less sense as to my previous post about preparing for G/A. On the other hand, flying around with a nose heavy airplane close to the ground seems to be risky business should the AP suddenly disconnect.

So the question remains why the AP trim the airplane in this way so close to the ground. Doesn't seem to be any obvious logic to it. I mean doesn’t this trim go against the fail-passive definition? During fail-passive operations should the autopilot disconnect the airplane should be in trim which it clearly isn't below 400 feet RA?

The fact is that anything more nose heavy than in trim at this particular stage would in my opinion be an accident waiting to happen. So maybe that’s the answer? We heard that on the 757 there is a distinction between LAND2 and LAND3 (fail-passive and fail-operational). Maybe this is a safety precaution when getting close to the ground? Scenario; AP disconnects just before minima and you have insufficient visual cues. Time for a GA, right!? Well in this case the nose or the control column pressure will tell you exactly where to go: UP not down. The natural response will be to TOGA and to get that GA thrust in there… and then you got some trimming to do but at least then there will be no doubt about where you’re going... or supposed to be going.

During a dual channel app you are expected to let the AP do the landing, if a non-normal scenario presents it self the airplane will in a pretty obvious way suggest what it thinks you should do. During a single channel app this is not the case since you are expected to disconnect at the appropriate time.

16th Jan 2005, 16:28
MrL RTFQ??? Why nose up trim? Please read some of the possible reasons posted previously.

CrossBars your comment “the airplane should be in trim which it clearly isn't below 400 feet RA”, is an often quoted misunderstanding; see:
JAR–OPS 1.435 Terminology.
“Fail-Passive flight control system. A flight control system is fail-passive if, in the event of a failure, there is no significant out-of-trim condition or deviation of flight path or attitude but the landing is not completed automatically. For a fail-passive automatic flight control system the pilot assumes control of the aeroplane after a failure.”
Also see: JAR-AWO 109 Out-of-trim forces at disengagement
“It must be possible to disengage the automatic landing system at any time without the pilot being faced with out-of-trim forces that might lead to an unacceptable flight path disturbance.”
Therefore, it may be assumed that Boeing has demonstrated that the out of trim forces in the 737 are acceptable.

Re MrL your comment “What is your opinion???? If the AP disengages just after the decision to land, what would you do?? The thinking here is that runway contact is almost certain if a GA is executed. The result we are after is an A/C safely on the deck.”

There is another widely held misconception relating to completing a manual landing after an autopilot failure, see:
“IEM to Appendix 1 to JAR-OPS 1.430, paragraph (e)(5)
Crew actions in case of autopilot failure at or below decision height in fail-passive Category III operations.
For operations to actual RVR values less than 300m, a go-around is assumed in the event of an autopilot failure at or below DH. This means that a go-around is the normal action. However the wording recognises that there may be circumstances where the safest action is to continue the landing. Such circumstances include the height at which the failure occurs, the actual visual references, and other malfunctions. This would typically apply to the late stages of the flare. In conclusion it is not forbidden to continue the approach and complete the landing when the commander or the pilot to whom the conduct of the flight has been delegated, determines that this is the safest course of action. Operational instructions should reflect the information given in this IEM and the operators policy.”

Thus, I would interpret the above as a GA should always be flown, unless unsafe to do so. Any alternative interpretation, without obvious problems e.g. engine failure, generator trip, etc, would require an understanding of why a continued manual landing is safer than a GA. I would further suggest that crews do not have the expertise to judge why a manual landing would be safer in limiting visibility conditions. N.B touching the runway during a GA is not inherently unsafe, whereas landing on grass is.
Could someone give an operators interpretation of this (ops policy) as suggested by the IEM?

16th Jan 2005, 23:07

You say: But somebody is of a different opinion...

Looks like trouble for you.

Two questions arise. I don't know the 737 - as I'm just an ATR driver, so:

First: What does the AFM say about any alarms on a CAT III approach and the subsequent procedure to apply?
(Does it maybe say something like - GO AROUND?)

Second: What does your companies operation manual or procedure manual say about "ANY" alarm on an armed CAT III approach?

Ours says: GO AROUND! Simply because you cannot tell the system implication within - lets say (300 ft) = 20 sec? !!!


Alaskan Timber
17th Jan 2005, 09:18
error 401,

The issue is that there was no OFFICIAL alarm. There was no up trim at 400ft, which is no OFFICIAL check item either. LEM wants to know why there is no OFFICIAL check (call) in his company OM, neither in the B737 FCOM.

Although LEM was not very fortunate in his sentence build up. I think he deserves a bit more credit from some of you. He just wants to share an experience with us.

17th Jan 2005, 09:53
LEM, Alaskan,

Sorry for the misinterpretation.

Just a thought:

Even if there is no official alarm, obviously the system has a means of telling you that something screwed up. If it where a really minor thing than it may never show on the flight deck but would be limited to a read out for maintenance somewhere hidden in the gizmos behind your backs. So someone thought of it being at least so important to notify the pilots.

If unsure of a systems behaviour and at 400 feet (which I'd consider rather a safe altitude) would a go-around not be the safest way to cope with this "non-alarm" situation.

Not being 100 % sure about a systems behaviour when one parameter is missing i'd rather choose that option.

Maybe a continuation could be considered when absolutely sure that it won't affect the landing and you may even have played with that failure in the sim once or twice.

As for the OM or AFM - It's not the bible - so sometimes they do not think about every failure. The wording in LEM's OM might be interesting. Does it say something about "any" failure on a CAT III approach should lead to a go-around ... or is it fully specific with details on the various occurrences?

17th Jan 2005, 10:02
Alaskan - I do not know enough about the detail of the 737 system, but IF this failure were to produce a 'Stab out of trim' warning, the QRH calls for a go-round. IF it does not, then LEM's question needs to be addressed. Can anyone say if it would produce the warning?

Alaskan Timber
17th Jan 2005, 10:42
Hey error 401,

The credit thing was not meant for you.

I agree a lot of failures during a CAT III require a go-around and if unsure about something 99.9% I would make a go-around (the .1% is a double flame out).

My books are 200 NM seperated from me, so I cannot check it. The questions stays : Is the 400ft trim a requirement or not ? Does the aircraft always trim at 400ft whatever the IN TRIM or OUT OF TRIM (no STAB OUT OF TRIM light) situation is ? Or can it anticipate on this ?

What I know is that the 400ft uptrim is a preparation for the flare. If you notice that on the FMA the FLARE doesn't engage (green) then in a normal situation you are allowed to land manually. After A/P disconnect the aircraft is already in the postion to land (due to the trim at 400ft). It is even mentioned not to pull the stick anymore as you might start ballooning.



Our posts crossed each other. I understood from LEM's post that he didn't get a STAB OUT OF TRIM warning. Otherwise it is 100% a go-around.

17th Jan 2005, 11:11

Thanks for clarification on the credability issue.:ok:

Can you come back on the post once you are again united with your books?

I'd really like to know what company and manufacturer say about "any" failure or malfunction (or indication thereof) on an established CAT III.

Any chance that someone knows someone at Boeing to get some insight on the tech side from the source?

17th Jan 2005, 11:13
I understood from LEM's post that he didn't get a STAB OUT OF TRIM warning. Otherwise it is 100% a go-around. - I did too, Alaskan, but to be pedantic, LEM did not SAY that, and we have to remember also that, as 'safetypee' and others have said, the simulator is only as good as its computer programme, and it is important to know whether the failure to trim would produce a warning on 'the real thing'.

I have always 'verbalised' the trim, even on a Cat I approach, as I consider it to be part of airmanship, but there is NO QRH action if it does not happen. I believe I was once told that the landing would be firmer but not unacceptable, but I have no documentation for that.

Someone said earlier that the 737 classic would autoland with single a/p? I really doubt that as there would be no flare function armed. Can anyone substantiate that?

17th Jan 2005, 12:03
I can confirm the 737CL sim behavior on single AP. In fact, during a sim session with a 25,000h something instructor which had flown everything from the -200 to the various NG:s, specifically showed us this feature as a nice to know in case everything else goes out the window. We actually did it SE if I remember correctly.

The reason why the FLARE mode wouldn't be armed seems quite obvious since this is not a certified procedure. Just because the graphic isn't there on the screen doesn't mean the AP isn't prepared for it.

On the question on trim req for flare or not, I think that the behavior of the AP system on the 757 gives a good clue. LAND2 - trim. LAND3 - no trim. This seems to be a question about the fact that this is a fail-passive procedure.

Any chance that someone knows someone at Boeing to get some insight on the tech side from the source?

I'll try to get hold of a former 737 technical pilot I know, who by my knowledge never been presented with a question about the 737 he's been unable to answer. :8

17th Jan 2005, 22:03
Yes, as Alaskan Timber rightly says, my sentence build up is often unfortunate, my English being quite poor.

But... who cares!!:E
I'm a pilot, not a politician, nor a demagogue, as somebody on this forum.
When I mean bread I mean bread, when I mean wine I mean wine.

So, enough blah blah and back on stage!


"If, during a CAT III approach, a system failure occurs which requires intervention by the pilot, a go around will be performed, unless the aircraft is below DH and the Captain has adequate visual reference to complete a manual landing."

Also: "If a system malfunction or engine failure occurs below DH, the Captain may, provided adequate visual references exist, continue the approach and land manually."
(Italic is mine).

Some posters have expressed their concernment about manually landing in poor visibility, accusing me of machismo, disconcerting attitude, pushing the airplane beyond its limitations and rubbish like that.

I thought that legally meant safely, in aviation.
Have you ever realized we are allowed lo legally land with a 15mtrs visual segment, although displaced due to the slant visual range?
Disconcerting, isn't it?

How come 15 mtrs?
My book says: if after passing the OM or equivalent position the RVR decreases to below minimums, the pilot is allowed to continue down to the radio minima, and land if he is satisfied with the visual cues.
Now, once again, adequate visual cues means THREE longitudinal lights, i.e. THREE runway centreline lights, which can be spaced as close as seven and a half metres!
That gives a segment of 15 metres!
And, just to add to the fun, all this is perfectly valid in CAT II, with the addition of one lateral element, being one TDZ barrette.

Correct me if I'm wrong with all this math, but CAT II means manual landing !

Now, I understand some decades ago the idea of an airplane landing by itself was unbelievable to the general public, so I understand how people involved with the certification process have tended to cover their *** as much as they could.

So, as a last resort, if everything goes to worms and our pilots are sleeping, let's give us a last chance adding this uptrim which will prevent making a big hole into the runway.

So now I've got at least two questions: why isn't there a warning if uptrim doesn't occur?
Why don't we have a callout for that? And why in the long and detailed list of all the required working components - and downgradable ones - there is no mention at all about uptrim?
In my manuals I cant't find anything about "... verify uptrim has occurred at 400 ft...", and I'm convinced some people won't even notice the lack of it.

And now the pilots aspect: how much do we want to trust them?
Why do two pilots need an uptrim if two autopilots, two red disconnect lights, an aural warning, a stab out of trim, and their ability to pull up manually are not enough to avoid making a large hole into the runway, when the same pilots are legally allowed to manually land an airplane after a CAT II approach with a visual segment available as low as fifteen metres?


One important clarification: I said my decision was to land after the no uptrim event, not that I actually landed.
In fact, after the ramark of the boss, I did go around at more or less 250 ft.

There still was no STAB OUT OF TRIM light.
And I've got the impression that it doesn't come on, if the uptrim doesn't take place.

So, of course, if the light actually comes on, maybe at a later stage, this whole thread is invalid, although quite interesting and stimulating...

But if it doesn't, I think my points deserve some attention...


Regarding the "rewarding" question, I just laugh at people considering it machismo.
I do confirm, yes, I'm rewarded when I safely land in "difficult" conditions.
Landing in CAT II or III is more difficult than landing in good weather. That's why not everybody can do it. One need to be qualified. It goes by itself.
So that's rewarding for everybody.

But in openly saying that, I make the other narcissist guys feel uncomfortable, as they think only they can secretly be rewarded.

Narcissism wears all sort of masks and garnments, including the humility one.
Know the little joke of the old man about to pass over, all his relatives and friends around his bed enumerating his virtues?
Eventually, he raises and says: " You have forgotten my humility!"

:E :E :E

18th Jan 2005, 22:21
Some observations on LEM’s post.
From my experience there is very little in aviation that is legally sound; the best course of action is “to do, and be seen to do” the correct thing for the circumstance i.e. take the safest option. With this in mind, it would be preferable for an operator to have SOPs for those abnormal circumstances where the captain has to satisfy himself with the visual cues e.g RVR below minima after OM.
Specific policy/procedures should define less restrictive visual cues in the event of a system failure; e.g to aid the crew in aligning or correcting a deviation resulting from an engine failure. In the event of an incident, it is more difficult for an individual to show that the required level of expertise existed or that correct judgement was made in the circumstances, as opposed to using a careful pre considered SOP to cover such situations – a task for management.

The visual segment maths are fine, providing all runways have closely spaced lighting. In addition, I think that you have identified a weakness in the JAR-OPS wording which was drafted before the wider use of closely spaced ‘Cat 3b’ lighting. The initial draft of subpart E required use of minimum visual segments as determined by experimental flight trials (ECAC Doc 17). I recall that for Cat 2 manual landing, this was 250 m, but as the old 400m RVR limit has been reduced to 350/300m RVR, the vis seg may now be 225 – 180 m depending on aircraft type. The first point of contact and duration with the visual references are important aspects in assessing the aircraft flight path and alignment.

Cat 3 autoland required a smaller visual segment at 50 ft (90 m), approx 3 consecutive sets of ‘lights’. However, as the smaller ‘autoland’ visual segment would not give an equivalent level of safety for a manual landing (without guidance, HUD, etc), JAR-OPS Interpretive and Explanatory Material (IEM) suggests a GA for any failure above DH in RVR less that 300 m, but the wording is loose enough to allow manual landing below DH.

A good explanation of the relationship between RVR, visual segment, and slant visual range is given in the Airbus document Getting to grips with Category II and III Operations. (http://www.nathangb.com/wingfiles.htm)

Re RVR falling below the approach ban limitations. In stable fog conditions, typical of Cat 3, any change in RVR with time is normally very small. However, for blowing snow or dust then the change could be large and indicate weather conditions to avoid.
In Cat 2, the RVR is more variable due to fog forming or clearing. Even a ‘normal’ Cat 2 decision can turn out to be wrong if cloud or fog banks blow across the runway, thus ‘legality’ before or after DH, still requires good crew judgement. This means taking the safest option, which ideally has been well thought through on the ground and thus less likely to suffer human error in an unfamiliar airborne scenario.

Finely, the thread – uptrim. Most systems, such as uptrim are in an aircraft for a good reason; if they are important to safety there should be a warning or physical limit, although in older aircraft the manufacturers relied on a crew procedure. If the reason for the equipment is not known, then avoid making assumptions about any operation if it fails.
Thus, does the 737 have a light, limit, or procedure for no uptrim or system failure?

Alaskan Timber
20th Jan 2005, 00:39
Hey safetypee,

No light and no (hands on) procedure.

This means in case of two failures (1. No 400ft uptrim. 2. Flare doesn't engage (green)), your MANUAL landing (see my previous post) will be a lot harder than expected and hopefully on the main gear first.

Conclusion : Why not make the 400ft uptrim an OFFICIAL check ? And clearly state if a go-around is required or not.

Hey error 401,

There is no law saying to go-around for ANY FAILURE during a CAT III. Failures which don't affect your approach and if you are FULLY AWARE of the situation, you may continue. No fidling at low altitude of course.

20th Jan 2005, 19:08

Thanks for the answer. It was exactly meant as posted by safetypee and as you said. I was wondering "if" your OM would state something (than it would become a legal issue). Safetypee gave a nice answer in his post - that is a management thing to define an SOP including failing systems.

22nd Jan 2005, 00:00
hello every one,

cfr this uptrim business at 400ft for b737classic in a 2 autopilot cat3 approach i think we should keep it as simple as possible: if it is not somewhere necessary on safety grounds or not required by reg's, be assured mr boeing or any other airplane manufacturer would not go over to the trouble of designing/certifying this feature on cost grounds alone.

so, i would consider the lack of uptrim at 400ft, if noticed, a failure of the integrity of the automatic gizzmo's & unwilling to be in for some unexpected nasty surprises during subsequent flare/landing when least needed(cat3 wx conditions): would call something like:"no uptrim, go-around", disconnect the autopilots, push toga & do a manual go-around as per sop's an automatic go-around would only be performed on weather considerations only: eg. not enough visual cues at dh.

but i agree, it looks a strange & mystery failure.