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flap extension on 737

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Old 7th Jan 2013, 12:49
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flap extension on 737

Why is the max flap extension altitude limited at 20000 feet? Any specific reason for it?
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Old 7th Jan 2013, 13:21
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Tapshi,
You also chew with the mouth open and burp in public?

Last edited by de facto; 7th Jan 2013 at 13:24.
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Old 7th Jan 2013, 13:45
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From B738 Fctm:

"less maneuver margin to stick shaker exists for a fixed speed as altitude increases"
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Old 7th Jan 2013, 13:48
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Because that was the highest altitude in the relevant part of the flight test programme. No need to do it at greater FLs.

Last edited by kenparry; 7th Jan 2013 at 13:48.
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Old 7th Jan 2013, 14:04
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...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"
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Old 7th Jan 2013, 15:15
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pprune at its finest.

"Thumper, what did your father tell you?"
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Old 7th Jan 2013, 16:31
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While we have the 'intelligents' here - anyone understand the chewing and burping?
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Old 7th Jan 2013, 17:12
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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
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Old 7th Jan 2013, 23:21
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perhaps another reason why the Boeing aircraft with a Smiths box refuses an airport alt higher than 10,000 feet...
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Old 8th Jan 2013, 00:17
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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......
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Old 8th Jan 2013, 01:29
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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.
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Old 8th Jan 2013, 01:59
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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.
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Old 8th Jan 2013, 12:51
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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
I will take my coat now and get some time off

Last edited by de facto; 8th Jan 2013 at 12:55.
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Old 10th Jan 2013, 07:27
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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.
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Old 18th Jan 2013, 04:52
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Understood and your comments taken in a positive and constructive sense.
btw Thank you for the replies everyone
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Old 23rd Jan 2013, 08:11
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This comes out of FCOM chapter 9 - Flight Controls

Code:
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

Last edited by bArt2; 23rd Jan 2013 at 08:23.
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