flap extension on 737

[Tapshi]

Why is the max flap extension altitude limited at 20000 feet? Any specific reason for it?

[de facto]

Tapshi,
You also chew with the mouth open and burp in public?:E

[Fullblast]

From B738 Fctm:

"less maneuver margin to stick shaker exists for a fixed speed as altitude increases"

[kenparry]

Because that was the highest altitude in the relevant part of the flight test programme. No need to do it at greater FLs.

[BOAC]

...and as someone pointed out in one of the many threads about this

"Why would you want too? How many airfields do you know above 17000ft?AMSL":)

[ImbracableCrunk]

pprune at its finest.

"Thumper, what did your father tell you?"

[BOAC]

While we have the 'intelligents' here - anyone understand the chewing and burping?

[Fullblast]

It's not important if anyone understand or not, the fact you ask is self explanatory that those kind of comments are out of place. This is supposed to be a professional forum, and this section a technical one, not yours or Defacto chat.

FB

[FlightPathOBN]

perhaps another reason why the Boeing aircraft with a Smiths box refuses an airport alt higher than 10,000 feet...

[Mach E Avelli]

Actually, 20,000 feet is a common enough certification standard and is likely to be quite arbitrary. If there is no requirement to extend the test parameters beyond that, why go to the expense?
Like the common 8 or 10,000 feet bird impact speed limit with windshield heat inoperative. But AFMs may be written that this limit is 10,000 feet AMSL rather than AGL, so what happens when you are over mountains where eagles fly? Common sense prevails, one would hope......

[FlyingStone]

Additionally, certification for use of flaps above FL200 would probably also require determination of flap placard speeds in terms of Mach number (as is the case for landing gear).

In any case, I don't think there is any need for Boeing to certify use of flaps above FL200 on any current jet aircraft.

[Spotlight]

Rather! It was discovered in earlier testing programs, British not Boeing that large electric motors would arc in less dense atmosphere.

At what altitude will they not arc with the insulating alloys (heavy) that we understand?

Twenty thousand was roughly the figure and development proceeded with this understood baseline.

Thus a limitation became a standard on the drawing board for the design of modern airliners.

Hydraulics, not without their own problems of rubber seals, purity and type of oil and flammability overcame a lot of this of course! Hence speedbrakes and hydraulically controlled control surfaces.

Now! If the aircraft you are flying has a limitation for flap or gear extension, respect it as it is likely that it has only been designed and tested to that parameter.

Some of the earlier posters should pay more attention in class and have the wit to understand that whatever they are now, they are not the finished product. Knowledge grows with time.

[de facto]

Eh Tapshi...

'Please','thank you' ...are terms that do exist.
All your post are the same (even I admit some are interesting questions) as not a single polite request.As people here owe to answer questions you may have.
Hence the comment on burping and chewing...general education..

Fulblast,I see your comment is quite useful as well:ok:
I will take my coat now and get some time off :oh:

[Mach E Avelli]

Thread drift warning and sorry, but to follow up on de Facto's comment.
Recently I was anchored in my little yacht having a nice afternoon nap.
Next I hear a female voice shouting "hello you MUST help us"
I look out and see these idiots have tried to cut between me and the shore and gone hard aground.
They were in no immediate danger, but she kept yelling "you MUST help us, you come and tow us off" etc.
Even though it was obvious I could hear her, I just kept asking her to repeat. She did not get it until her mate worded her up to use the "please" word. Whereupon I rendered assistance.
So yes, Tapshi, next time please use the P word, and maybe thank those of us who take the time to answer.

[Tapshi]

Understood and your comments taken in a positive and constructive sense.
btw Thank you for the replies everyone

[bArt2]

This comes out of FCOM chapter 9 - Flight Controls


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

I find this book to be handy giving a lot of info, although not always with enough detail.:}

Bart