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B737 Maximum Flaps Extended Altitude

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B737 Maximum Flaps Extended Altitude

Old 26th Mar 2013, 21:26
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B737 Maximum Flaps Extended Altitude

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.

Thank you

Last edited by Breakthesilence; 26th Mar 2013 at 21:30.
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Old 26th Mar 2013, 22:25
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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?
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Old 27th Mar 2013, 00:26
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What a ridiculous question

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
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Old 27th Mar 2013, 03:38
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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.

Last edited by de facto; 27th Mar 2013 at 03:41.
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Old 27th Mar 2013, 15:07
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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.

Last edited by Breakthesilence; 27th Mar 2013 at 15:08.
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Old 27th Mar 2013, 15:27
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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: ?
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Old 27th Mar 2013, 15:46
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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...
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Old 27th Mar 2013, 16:40
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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.
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Old 28th Mar 2013, 12:55
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Once again proof there are stupid questions.
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Old 28th Mar 2013, 14:16
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Originally Posted by Breakthesilence

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.

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.
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Old 28th Mar 2013, 16:01
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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.
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Old 28th Mar 2013, 17:28
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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!

Last edited by Breakthesilence; 28th Mar 2013 at 17:30.
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Old 28th Mar 2013, 22:04
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Originally Posted by 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.



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.
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Old 29th Mar 2013, 02:44
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You may want to share the http://www.pprune.org/tech-log/51113...ransports.html thread with your instructor. And I would confirm the wording is the Boeing approved version regarding flap extension above 20k.
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Old 29th Mar 2013, 04:13
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- 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?
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Old 29th Mar 2013, 04:58
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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.
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Old 29th Mar 2013, 05:09
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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.
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Old 29th Mar 2013, 08:24
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The list of posters here who are completely failing to answer the question is staggering. Let me do 'a Clandestino'?

Originally Posted by exeng
20.000 ft limitation
- in terms of the wording, there is no '20000ft limitation'.
Originally Posted by de facto
particularly on maneuvring issues.
- tell us what these are.
Originally Posted by FlyingStone
it's the flaps extended,
- your test results showing this?
Originally Posted by aterpster
Once again proof there are stupid questions.
- waste of server space!
Originally Posted by busserday
You may want to share the http://www.pprune.org/tech-log/51113...ransports.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!
Originally Posted by SMOC
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'.
Originally Posted by b44
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.
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Old 29th Mar 2013, 08:53
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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.
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Old 29th Mar 2013, 09:11
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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?

Last edited by SMOC; 29th Mar 2013 at 09:30.
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