B737 Maximum Flaps Extended Altitude

[Breakthesilence]

Hi guys,

in the Limitation section of the AFM (and FCOM) of the B737 Classic, the limitation states the following:

- Do not extend flaps above 20,000 feet pressure altitude.

Now, let's say you take off and have a Flaps asymmetry during retraction, the airplane is well under control and you decide to continue flight to your (short leg) destination for different reasons (company base, maintenance ecc.).

Can you climb above 20,000 feet with Flaps extended?

It seems, reading the aforementioned limitation, that you are only limited by the Flaps extension (thus, the "operation" of the flaps and not the flaps already extended).
The Non Normal Checklist covers this trouble (asymmetry) during approach only. I checked the 737 MRG book too, but it says nothing more than to avoid using FMC fuel prediction in case of continuation toward the destination.

I just want to know if you are legally authorized to do it and not if you would or wouldn't do that because of Mach effect etc. :ok:

Thank you

[FlyingStone]

My bet is on no since aircraft wasn't flight tested with flaps extended above 20.000ft and is therefore not certified for such operation - nor is it likely that it will ever be, given that no airport in the world requires use of flaps above FL200.

BTW, if it's a short leg and assuming you have appropriate amount of fuel to fly to preferred airport, why even bother with flying outside of certification scope?

[exeng]

No Pilot would exceed the 20.000 ft limitation knowingly.

If you had a flap problem on departure then your main concern would be:

a) the landing flap configuration
and:
b) the most suitable airfield to land

[de facto]

Worrying ...
Why would anyone even think about flying at high altitude with flaps assymetry?
I suggest you read about high altitude flying,particularly on maneuvring issues.

[Breakthesilence]

First of all, I'd like to express my disappointment to Exeng, there are no ridiculous questions anywhere in any subject, only stupid answers (like yours).

Why did I ask that? Because you, as a pilot, have access to different manuals. If none of these manuals report the certification of flight with flaps EXTENDED but only "flaps extension altitude" (this is my concern, the way it is written) how could you know that flying already with flaps extended above 20000 feet is out of limits?

I would never fly above that altitude with flaps extended, but as I was discussing with an instructor who would do that, I'd like to find something to be proved legally.

In simple terms, how could you prove you are out of limitations if you are not EXTENDING the flaps above 20000 feet, but you are actually climb above that altitude already in that configuration?

I hope this clarify my question...otherwise, I think you don't like to listen.

[FlyingOfficerKite]

there are no ridiculous questions anywhere in any subject, only stupid answers

Question: 'Having watched the movie 'Flight', would it be possible to replicate that inverted approach in a B737 and roll out to a safe landing. There's nothing in the manual on the subject?'

Sensible answer: ?

[FlyingStone]

I thought it is logical to understand that it is not the extension process (e.g. flaps going for example from 0 to 5) that is the issue above 20.000ft, it's the flaps extended, since aircraft hasn't been tested with flaps extended at higher Mach numbers. Therefore, Boeing has only provided maximum flap speeds only in KIAS - do you think it's really safe to fly at FL370 at M.75 with 240 KIAS and flaps 5 (limitation for F5 in -400 is 250 KIAS)?

AFM limitation:

Maximum flap extension altitude is 20,000 feet pressure altitude.

FCOM:

To prevent excessive structural loads from increased Mach at higher altitude, flap
extension above 20,000 feet should not be attempted.

Sometimes a bit of logic helps, but as it appears not with everyone...

[Breakthesilence]

I thought it is logical to understand that it is not the extension process (e.g. flaps going for example from 0 to 5) that is the issue above 20.000ft, it's the flaps extended, since aircraft hasn't been tested with flaps extended at higher Mach numbers. Therefore, Boeing has only provided maximum flap speeds only in KIAS - do you think it's really safe to fly at FL370 at M.75 with 240 KIAS and flaps 5 (limitation for F5 in -400 is 250 KIAS)?

AFM limitation:

Quote:
Maximum flap extension altitude is 20,000 feet pressure altitude.
FCOM:

Quote:
To prevent excessive structural loads from increased Mach at higher altitude, flap
extension above 20,000 feet should not be attempted.
Sometimes a bit of logic helps, but as it appears not with everyone...

That's what I think too, as said, I'd never fly above 20000 feet flaps extended; it was just a discussion with a colleague that prompted me to find something printed clearly.

[aterpster]

Once again proof there are stupid questions.

[JammedStab]

I just want to know if you are legally authorized to do it and not if you would or wouldn't do that because of Mach effect etc. :ok:

Thank you

I'd say that you are legally authorized to break the rules in the event of an emergency. In other words, you can't get back into your departure airport and will run out of fuel if you don't get up to a higher altitude, then you have a justifiable reason to be acting as the equivalent in this case of a test pilot.

More of a remote area ops scenario.

[BOAC]

BtS - we are probably into semantics here, but you are correct - the driver's handbook does not prohibit flight above 20k with flaps extended.

I suggest the intention of the restriction is self-explanatory? However, I do not expect anything dramatic is going to happen at 20001' in your scenario that would not happen a 19999', so I say "if you have to...................you have to". You would certainly get reasonable notice that things are not going too well, I think, as you climbed.

I can, like you, think of very few scenarios where you might want to do it.

[Breakthesilence]

The scenario, regarding the discussion with the colleague, was:

- Take Off from an airport with no assistance by maintenance, 50 min flight time to destination that is our home base (the only one along the route and with full maintenance assistance etc.) which offers 3 long runways. Weather is excellent everywhere and no mountains are there to make you concern about them.

- Fuel is 100-200 Kg more than minimum; anyway, not enough to reach the destination if flying with flaps extended at low flight levels.

- Plenty of suitable airports along the route.

I'd say that you are legally authorized to break the rules in the event of an emergency.

That's right but in this case we have to first clarify if "breaking" the 20000 feet limit is legal or not!

[JammedStab]

The scenario, regarding the discussion with the colleague, was:

- Take Off from an airport with no assistance by maintenance, 50 min flight time to destination that is our home base (the only one along the route and with full maintenance assistance etc.) which offers 3 long runways. Weather is excellent everywhere and no mountains are there to make you concern about them.

- Fuel is 100-200 Kg more than minimum; anyway, not enough to reach the destination if flying with flaps extended at low flight levels.

- Plenty of suitable airports along the route.



That's right but in this case we have to first clarify if "breaking" the 20000 feet limit is legal or not!

Land at one of the suitable airports and have the company deal with it. A maximum altitude is like a minimum weather requirement. It is a limitation. And you do not have an emergency.....although, I suppose you could declare one.

[Busserday]

You may want to share the http://www.pprune.org/tech-log/511131-high-altitude-stall-characteristics-jet-transports.html thread with your instructor. And I would confirm the wording is the Boeing approved version regarding flap extension above 20k.

[SMOC]

- Fuel is 100-200 Kg more than minimum; anyway, not enough to reach the destination if flying with flaps extended at low flight levels.

How did he come up with the fact you can make it above 20, 000' as you stated the FMC doesn't account for flap extended like it doesn't account for gear extended, FCOM 2 would have no perf figures for flap above 20, 000'. You can't assume Fuel flow and ground speed would be better.

What will happen when suddenly you hit the sweet spot and flutter rips your asymmetric flap off or your outboard aileron etc.

Is your colleague a test pilot?

[bubbers44]

Quite simple, if the flap limit is 20,000 ft, don't exceed it. My Jetstar gear wouldn't retract going from LAS to LAX one day so we stayed at FL200 and maintained max gear extention speed. It took 20 minutes longer but our passengers didn't have to wait for an extensive maintenance delay.

[bubbers44]

Flight, the movie, might have been tried by Alaska Airlines because they were going to die anyway but we all know flying inverted is not going to save any lives because even if the wings don't fail at some point when you roll upright you will dive into the ground with the HS jackscrew problem they had.

[BOAC]

The list of posters here who are completely failing to answer the question is staggering. Let me do 'a Clandestino'?

20.000 ft limitation - in terms of the wording, there is no '20000ft limitation'.particularly on maneuvring issues. - tell us what these are.it's the flaps extended,- your test results showing this?Once again proof there are stupid questions. - waste of server space! You may want to share the http://www.pprune.org/tech-log/51113...ransports.html (http://www.pprune.org/tech-log/511131-high-altitude-stall-characteristics-jet-transports.html) thread with your instructor. And I would confirm the wording is the Boeing approved version regarding flap extension above 20k. - your link has no reference to flaps. As far as I know there is no 'instructor' involved in this query. We know the wording. The meaning was what the question was about! How did he come up with the fact you can make it above 20, 000' as you stated the FMC doesn't account for flap extended like it doesn't account for gear extended, FCOM 2 would have no perf figures for flap above 20, 000'. You can't assume Fuel flow and ground speed would be better.
What will happen when suddenly you hit the sweet spot and flutter rips your asymmetric flap off or your outboard aileron etc.
- no-one is saying you can, but the question was 'is it ok to try'? I take it you would have no 'flutter' worries at 19,999'? 737 does not have an 'outboard aileron'. Quite simple, if the flap limit is 20,000 ft, don't exceed it. - which flap limit is that?

BtS - I think you will have to give up here since no-one actually knows the answer. You could try Boeing, but since there have been no (official) tests above 20k involving flaps as far as I know they would probably say no. Your choice would be try it, succeed and get a 'chocolate nose' award from company, or possibly write off the a/c.

Mach number and its effect on flaps will be your problem. Personally, unless things were desperate, I would, like JammedStab, try to persuade company to let me spend a few days at a 'choice' diversion with decent facilities.:)

[Pontius]

I agree with you, BOAC, regarding some of the answers here, with sage-like advice and rude criticism from people who haven't bothered to read the question. I think it would have been better if BTS had excluded the scenario from his question and simply asked about extending the flaps above 20000', as opposed to leaving them already extended above 20000'.

Clearly there are issues to extending various various bits of metal into the airflow, versus leaving them there and that's why, for instance, there are differing speed limits for gear lowering and gear extended etc (this is only an example and I do understand the reasons behind this particular case). However, I think FlyingStone best answered the question with his quote from the FCOM:

To prevent excessive structural loads from increased Mach at higher altitude, flap extension above 20,000 feet should not be attempted.

Although it only refers to actually extending the flaps (as opposed to leaving them already extended) the FCOM is quite clear that Mach number is the problem and is, therefore, suggesting the 'excessive structural loads' will be present when the flaps are extending, as well as when they're extended, so the limitation applies to both scenarios. I say 'suggesting' because it doesn't clearly state that.

Doubtless there are those who will sarcastically say 'duh, it's obvious' but they are the same people who didn't read the question properly in the first place and consider 'extending' and 'extended' to mean the same thing.

[SMOC]

no-one is saying you can, but the question was 'is it ok to try'? I take it you would have no 'flutter' worries at 19,999'? 737 does not have an 'outboard aileron'.

Why the hell would you want to try?

Of course there are no issues at 19999' nor probably at 21000' but the limit it there simple.

I know the 737 doesn't have an outboard aileron that's why I added the etc does it matter which A/C or are you saying it's Ok because it doesn't have one? The 747 has the same 20000' limitation the point being you don't "try" flying outside the certified envelope, our job is to get people safely from A to B not try things because we think there is a loophole in the manuals.

It's probably safe till FL250 however Boeing probably said make it FL200 for the idiots that want to "try".

Nothing against the question I just find it amazing that people are possibly being trained that it is ok to bend the rules if you think it's not black and white and then do a check on a guy based on the grey?

[Pontius]

the limit it there simple.

I think was part of the point being made, SMOC, the limit is not specific enough to be a limit. The limitation says do not extend flaps, it doesn't say don't fly with flaps extended above 20000'. If that's what they mean (and I'm certain in my own mind they do) then Boeing should write it.

I agree with you that we should not be trying to this, nor should we attempt to be Boeing test pilots, however, in my opinion, the poor English used in the AOM opens Boeing to challenge if someone were to go above 20000' feet with flaps extended and it all went wrong. Semantics, yes, but that's what lawyers love when big industry cocks up.

[SMOC]

Pontius, likewise, I guess the world is becoming a place where everything has to be written and common sence has no place, it'll never stop, the next question will be it doesn't say I can't do barrel rolls so can I try? I know extreme the mind boggles when pilots can't think of the "intent" Asia is full of its "not written" shame the Western world is going down the same path.

[Breakthesilence]

I'm very impressed by the very low number of users who really understood my question.

How can someone expect a professional and serious answer if so many don't even spend 2 seconds reading and understanding the question.

English is not my native language, maybe I was not so clear in the initial message but I believe I'm not the only one in fault here.

That's obvious that braking a rule (better...braking a limitation) outside an emergency situation is not professional and not even safe.

As those ones, really few, who correctly understood my question said, we are not braking any AFM-FCOM etc Limitation...looking the papers.

I was just trying to find (that's why I asked your help) a document where something clearer was stated because I might have missed it!

[By George]

Captain 'Hoot' Gibson of TWA 727 fame, is the man to ask about flaps at high altitude. I think it's called, 'the other way to get down'.

[SMOC]

Can you climb above 20,000 feet with Flaps extended?

Yes

Can you do a barrel roll?

Yes


The limitation is for A/C configuring for high altitude airfields not for use in an abnormal situation.


George :ok: exactly.

[Pub User]

This is an anonymous forum. I hope there are a lot of MS Flight Sim pilots here.

[aterpster]

By George:

Captain 'Hoot' Gibson of TWA 727 fame, is the man to ask about flaps at high altitude. I think it's called, 'the other way to get down'.

He certaintly is. He would refer you to Boeing and today probably cite the 787 as an example of Boeing's methods.

As a fellow TWA pilot may I add, as I have before, neither the FAA nor the company faulted that crew. The NTSB did because they were in Boeing's pocket at the time.

Now, many years later, the FAA is in Boeing's pocket instead of the NTSB.

[aterpster]

breakthesilence:

I'm very impressed by the very low number of users who really understood my question.

How can someone expect a professional and serious answer if so many don't even spend 2 seconds reading and understanding the question.

English is not my native language, maybe I was not so clear in the initial message but I believe I'm not the only one in fault here.

That's obvious that braking a rule (better...braking a limitation) outside an emergency situation is not professional and not even safe.

As those ones, really few, who correctly understood my question said, we are not braking any AFM-FCOM etc Limitation...looking the papers.

I was just trying to find (that's why I asked your help) a document where something clearer was stated because I might have missed it!

I read your entire first post the first time.

No one in their right mind, who is actually a real airline pilot, would come even remotely close to doing what you proposed.

Now, go back to your MSFS and have fun.

[BOAC]

Captain 'Hoot' Gibson of TWA 727 fame, is the man to ask about flaps at high altitude. - to introduce this 'history' into this thread demonstrates a complete lack of understanding of aircraft performance and the topic.

Why not tell us EXACTLY what happened and then everyone will see the irrelevance of the posts. Did he climb above 20k with flaps extended? Did he extend flaps above 20k contrary to the limitation?

[Breakthesilence]

I read your entire first post the first time.

No one in their right mind, who is actually a real airline pilot, would come even remotely close to doing what you proposed.

Now, go back to your MSFS and have fun.

Aterpster, please, quote any post where I "proposed" to fly above 20000 feet with flaps extended.

I always respect my colleagues, virtual or real, but at this point I really think I'm not talking with people but actually monkeys; it's unbelievable how you are able to put down expression or ideas one has never expressed!

Before sending me to play Flight Sim, I can send you to play toys in diaper, than you could start learning how to read and maybe in few years you'll be able to write down your name.

I will not fall in the game "I'm a real pilot, I have XXXX Flight Time etc."; I don't have to disclose my CV to anyone to face your invitation to MSFS.

Here is a self quote from post number 5:

I would never fly above that altitude with flaps extended, but as I was discussing with an instructor who would do that, I'd like to find something to be proved legally.

[john_tullamarine]

Chaps,

Time to retire to the various corners of the ring and count to ten. Saves me the trouble of wielding the big stick ... far prefer rational thought to return to the fray.

The guiding light remains "play the ball, not the player"

[aterpster]

j.t.:

Time to retire to the various corners of the ring and count to ten. Saves me the trouble of wielding the big stick ... far prefer rational thought to return to the fray.

The guiding light remains "play the ball, not the player"

The "ball" in this game was the launch question:

Can you climb above 20,000 feet with Flaps extended?

Even as a hypothetical it was beyond the pale.

It was akin to me asking you, "If I lose an engine below Vmcg can I attempt a takeoff anyway?"

[Breakthesilence]

It was akin to me asking you, "If I lose an engine below Vmcg can I attempt a takeoff anyway?"

Come on...be serious, it's not the same kind of question, above all if you read that I was looking for sections of manuals or something written to support the misleading statement of Boeing's Limitation section of the AFM.

It was curiosity, search for something I was, probably, not able to find.

The concept is clear: it's not a great idea to fly above 20000 feet with flaps extended.

The curiosity: Had Boeing set such a limitation in any manual as I don't know if I'm missing it?

It's really, reaaaaally different from stating that I don't know or, worse, I'm willing to fly that way.

[FullWings]

Given the exact phrasing of the original limitation, I think the question was a reasonable one and did not deserve the offhand comments it has received.

There are plenty of aircraft systems which can have multiple limits on some types, like landing gear: one maximum for deployment, one for when it's down and yet another for retraction. Also can be IAS, mach or both.

On the 777, the computers won't let you deploy flap >20K which can be problematic if you have a certain type of static failure and the aeroplane still thinks it's at 30,000' even though you're nearly on the ground.

I'd guess there are sound aerodynamic/structural reasons why it isn't a good idea to fly around at high altitude with flaps/slats out, so Boeing have thought what might be needed for operational reasons (going in/out of Bogata, for instance), added a margin then rounded it up to 20,000'. The text doesn't say what exact configuration, so there would logically be less of a problem with F1 than F30.

It's one of those scenarios that rewards a little previous thought. Like BOAC, I don't regard 20K as a hard "wings stay on/wings come off" limit but would be reticent to exceed this unless it was to avoid something worse, like hitting a mountain or running out of fuel.

The answer to: "Can you climb above 20,000 feet with Flaps extended?" would be yes, of course, but only if you *really* need to. It takes quite a bit of imagination to get to that point but hey, you never know.

Also, "If I lose an engine below Vmcg can I attempt a takeoff anyway?", could be answered by yes as well. Not all attempts will be successful, depending on the exact circumstances! It's not something that's recommended either. ;) (Next time in the sim in a twin, try a single-engined takeoff from stationary - surprising what a non-event it can be...)

[cosmo kramer]

This thread is a good example of why I don't really contribute here anymore. Lot's of people with 1000s of post, claiming to be real pilots, who can't even read.

I found your initial question interesting, I don't know the answer either. I feel for you Breakthesilence, load of rubbish replies and insults. I salute you and am impressed that you managed not to sink into their levels. I probably would have, which is why I stay away, because every thread here tends to degenerate :(


As for the scenario, the question is "why do it?":

A 50 min flight is normally not planned much higher than FL300, so how much do you actually expect to gain comparing to flying at FL200? If in your scenario the home base has 3 runways and it's CAVOK, why not simply dip into the alternate fuel and complete the flight in FL200.

[Matey]

The very first reply has the answer as far as I am concerned (737 TRE) . The 20000 restriction is in place because the aircraft has not been flight tested/certified with flap above 20000. Will it fall out of the sky? Probably not, but it is unknown territory, hence the manufacturer's requirement

[Checkboard]

No one in their right mind, who is actually a real airline pilot, would come even remotely close to doing what you proposed.

I once flew as an FO with a CAA inspector in the left hand seat, where this exact question came up. The CAA inspector insisted that the limitation was specific about extending the flap, not operating with flap extended - and we proceeded to FL380 or so with a small amount of flap extended.

(There's more to that story, but that's the guts of it.)

So - yes, it's an old question. Yes, it can be misinterpreted, and yes where it can be misinterpreted there will be a pilot who will do it.

The limitation is standard on every jet aircraft I have flown, and like everyone else, I am convinced that it simply means "Flaps aren't tested in this region - here be dragons".

[nitpicker330]

You flew to FL380 with some Flap extended????????

I'd suggest that with your IAS below VFE your TAS would be way toooooooo fast for the poor old Flaps to not be damaged!!!!

Yikes.....

[Checkboard]

I said it was a small amount of flap. ;)

... and since when are flap limitations based on TAS? Indeed, what would TAS have to do with flap loads at all? :confused:

[WhyByFlier]

I think nitpicker is confusing TAS with performance. If you're at a high TAS low level you're at a high IAS too and almost certainly outside flap operating limits. If you are at a high TAS because of altitude then you're about to change a high speed wing into a lower speed wing. And that's if you're even able to get flaps out (the limitation part of a LOIN check) at high level given your inevitable high IAS ( 240-260 kts on the A320 at FL360+). And yes I know the PFD is actually displaying CAS/EAS.

[john_tullamarine]

Aterpster,

My admonition probably wasn't directed at your good self ...

Chaps,

The limit is a certification matter and has been done to death in previous threads on the subject. One of many is this one (http://www.pprune.org/tech-log/374224-max-operating-altitude-flaps.html). I note that MFS plays with this stuff day in day out in his day job ....

In addition,

(a) there are certification discontinuities at 20,000 feet

(b) the structural load capability with flaps is reduced compared to clean

in the Standards.

The real killer is that there is no obligation on the OEM to investigate high altitude operation with flaps. Unless the AFM indicates a permission to so operate, a general limitation is prescriptive. Bush lawyering is not useful when interpreting AFM matters.

In many respects there are things which are not explicity proscribed in aviation and this is one of them.

Consider what one's story might be at the Inquiry after the mishap should one have elected to play test pilot with someone else's aeroplane ...

Will be having dinner with MFS in a day or so, so will ask him his thoughts on the matter.

[BOAC]

Whilst I hope you enjoy your dinner, JT, you might wish to read MFS's contribution in your link at post #6 and I-2021 at post#9 in http://www.pprune.org/tech-log/278705-b737-flap-extension-above-20000-a.html where 300kts /0.65M would seem to be an absolute limit, and to lay the 'you're going to be a test pilot/die in flames' rubbish to rest, Checkboard at post #37 here.

BtS - as I said before, there is no answer the way Boeing have worded it. Hope you have some food for thought from the more 'thinking' contributors here. If some day you are in charge and you need to do it for whatever reason, it is your decision. (and ignore reference to TAS, by the way.'Tis IAS wot breaks things and Mach which causes control issues basically.)

As proven, Once again proof there are stupid answers.

[vilas]

Breakthesilence is asking legal interpretation of flap extension. He is not interested in theory of DOs and Donts. If Boeing permitted extended flaps beyond 20000 they would have said so. In absence of that it simply means flaps have to be up beyond 20000ft. Line pilot is not expected to find solutions when manufacturer has not provided them. According to me it is not permitted you need to land back.

[nitpicker330]

I'm not confused about anything chaps.

Lets assume VFE of 240 kts at FL200. Around 320 kts TAS.
VFE of 240 kts at FL380 equals about 450 TAS.

A much higher TAS and therefore Airload on the devices.

Naturally you'd have to be close to VFE during cruise at FL380 otherwise you'd be below Minimum Speed. ( in most heavy jets anyway )

That's all.

[BOAC]

OK nitpicker - your starter for 10-:

The International Space Station has a TAS of 17,239mph in orbit, but an IAS of practically zero. What are the air loads on the assembly? If it had 'flaps' and extended them, would they be ripped off because of the TAS?

[john_tullamarine]

and to lay the 'you're going to be a test pilot/die in flames' rubbish to rest

Good sir, I have a conservative view of life (boring old engineer and all) .. which gets more so as I get older, more doddery and less desirous of dying.

TPs get to have lots of boredom (for which the sensible ones strive) and the occasionally interspersed moments of terror (when something happens which they didn't expect) .. to let us mere mortals have an easier time of it and get all the excitement we need in the bar on overnights.

Rest assured that the topic is bound to be a dinner topic.

You cite Checkboard .. I quite liked his summation ... "Flaps aren't tested in this region - here be dragons". It's a bit like the old QA audit axiom .. "absence of evidence is not evidence of absence".

[BOAC]

get all the excitement we need in the bar on overnights - so - the rumours are true?....................:)

[john_tullamarine]

.. indeed ... I can recall waking up the next morning in some of the more highly regarded bars in places here and there ....

Ah, memories .. now, I'm on the slippery, slidey slope to Hell as a consequence.

[BOAC]

Let me give you one example of where I once flirted with death, and chose to leave the comfort of "all the excitement we need in the bar on overnights.", devil that I am.

I once (late 80's) took delivery of a Cessna 310R (on the British register) to be operated on my AOC in Scotland. A nice ship - fully booted, electric window and prop de-ice etc BUT the CofA said "Not cleared for flight in known or forecast icing". The type fully 'iced' in the US. I asked for the restriction to be changed - no.

Why? The necessary 'icing trials' on the 310R to satisfy good old Auntie had not been carried out. Now, my problem was, and I don't think it has changed, that icing was 'forecast' EVERY day in the Scottish FIR - a bit of a problem, really. My then Flt Ops inspector was one of the early sufferers from 'restricted timber vision' (wood and trees etc - I have other stories............) and I just KNEW my AOC, if not my ATPL, would be in peril at his next 'regular' inspection of minutiae. So, I gently enquired the cost of the 'icing trials' - and fainted. After significant to-ing and fro-ing (and those who have tried to run small AOCs will know what I mean), I FINALLY got the restriction changed to '"No flight in Known Icing conditions" (hoorah!)

You will never guess what I used to do on my flights, will you? - and I didn't crash or burn. Yes - I flew that aircraft in uncharted territory, and THAT was a restriction that was abundantly clear in its intent (and wording) too.

[Turbine D]

This discussion is very intriguing to me as an engineer. Here is a photo of the Boeing 737 Classic triple slotted TE flap extended.

http://i1166.photobucket.com/albums/q609/DaveK72/flapsdown_zps89ab0587.jpg
Triple slotted trailing edge flaps at the 40 position on a 737-400.

Now true enough, Boeing says not to extend the flaps above 20K feet as they never certified the aircraft in this configuration. I suspect they do know some things from a design analysis/stress point of view as to why this isn't a good idea, but never confirmed it in flight testing/certifying the Classic, and just said don't do it.
However, the story may be different in the Boeing 737-NG series. Here the flaps are double slotted, not triple slotted. And Boeing says this:
Although the flap placard limit speeds are different for each 737NG variant, the structural limit speed for the flaps is equal to the placard speeds (175k – F30, 162k – F40) for the heaviest variant (737-800/900). The Flap Load Relief trigger speeds (176k – F30, 163k – F40) are set to allow all variants to fly to the structural limit speed without system activation. Setting lower flap placard speeds for the –600 and –700 variants allows for greater service life of flap components due to the larger margins to the structural design speed.

For the NGs, speed is important, can you cruise and maintain level flight above 20,000 feet at less than 200k, 176k or 163k?

Going back to the Boeing Classic, Boeing says:
A flap load limiter (-3/4/500) / flaps/slats electronics unit (-NG) will automatically retract the flaps from 40 to 30 (-3/4/500) / also 30 to 25 (-NG) if the limit speed is exceeded. The flaps will extend again when speed is reduced.
At this point, I am assuming there to be an automatic sequencing of leading devises ( 2 Kruger flaps inboard of each engine) and 6 slats outboard of the engine per wing. So extending the TE flaps, these devises extend first, correct? If so, I wonder if there are stress limits determined by speed for these, more so than the TE flaps? Any thoughts, any one?

[galaxy flyer]

I'd add that with the LEDs extended the flow over the wing might be accelerated beyond Mach 1, which would add the the stress on both sets of high lift devices.

[zxccxz]

Guys: not an emergency, but the flight was continued..


Report on the low fuel incident of KL874, a Boeing 747-406, PH-BFC, en route from Bombay (VABB) to Amsterdam (EHAM), on 14 July 1994


Operator: KLM - Royal Dutch Airlines - Aircraft type: Boeing 747-406 Combi Registration: PH-BFC Flight: KL874, scheduled from Bombay Airport (VABB) to Amsterdam Schiphol Airport (EHAM) Date: 14 July 1994 Place: During descent into EHAM


Synopsis
After an uneventful take-off from Bombay Airport in heavy rain, the EICAS alerts "Flaps Primary" followed by "Flaps Drive" were triggered during climb, passing FL220, at an airspeed of approximately 330 kts. The respective emergency checklist procedure was performed and after some delay, due to poor HF communications, clearance was obtained from Bombay ATC to descend to FL200, in accordance with the emergency checklist procedure. KLM movement control and KLM maintenance support were contacted via HF radio and in concert with KLM maintenance support the flaps were recycled between positions 'up' and 5 several times, by use of all available operating modes. However the flap warning persisted and it could also not visually be verified that the leading edge flaps were fully retracted. It was decided that the flight could continue but that the respective flaps 5 limit speed should be observed. However in concert with KLM operational engineering, it was decided that the stated altitude restriction was not applicable and that the aircraft could climb, given the normal operational envelope and the additional speed limitation. An intermediate landing at Dubai was considered, but at that time the aircraft was still operating above its maximum landing weight. Fuel calculations indicated that the flight could proceed to Athens with 25.000 kg fuel remaining upon arrival. While the flight continued, it became apparent that it was also possible to continue the flight to Frankfurt. KLM movement control was informed and a technical team with spare parts was put on standby to proceed to Frankfurt as soon as the final decision was made to make an intermediate landing at Frankfurt. While the flight continued, fuel calculations indicated that KL874 might continue to Amsterdam with approximately 4000 kg fuel remaining upon arrival. Shortly before passing abeam Frankfurt, fuel calculations indicated slightly more than 30 minutes reserve fuel remaining upon arrival in Amsterdam and after consult (via KLM movement control) with the Schiphol Meteorological Office, Air Traffic Control and the chief pilot, it was decided to continue the flight to its original destination Amsterdam. After passing Frankfurt, the indicated amount of fuel remaining upon arrival however started to decrease and ATC did not clear KL874 for an unrestricted descent and approach into Schiphol. During descent it became apparent that the aircraft would land with less than 30 minutes reserve fuel. KL874 did not declare an emergency, but ATC was informed of the critical low fuel situation, after which KL874 was cleared direct to Schiphol. Due to a late descent cleararce, an intermediate level off at FL260, diverging radar vectors from ATC and early flap extension, to verify the correct operation of the flaps, the calculated remaining fuel decreased further and after parking at the gate it was noted that there was 2200 kg fuel left.

[john_tullamarine]

Far be it for me to second guess KLM. However, I can see an interesting time of it at the Enquiry had it all turned to custard.

I don't think that the corporate risk management approach necessarily would win hearts in all parts ...

[737Jock]

1994... explains a great deal I reckon.

[JammedStab]

Not too bright planning to continue to AMS with 4 tons remaining. How do I know. Look at their landing fuel. What about ATC delays or a go-around. What will that burn....3 tons. Will the flaps extend properly. FRA has plenty of things to do.

AIRMANSHIP (http://www.airmanshiponline.com/fall99/articoli/02a99-kl874.htm)

[737ngpilot]

My AOM...To prevent excessive structural loads from increased Mach at higher altitude, flap extension above 20,000 feet should not be attempted