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Landing With Assymetrical Flaps  
User currently offlineRNOcommctr From United States of America, joined Jan 2001, 834 posts, RR: 3
Posted (6 years 10 months 1 week 5 days 23 hours ago) and read 4977 times:

We had an Alert II here at RNO with an AA 757 landing with assymetrical flaps. The aircraft landed safely although it looked slightly crabbed on touch-down. I would guess that with one flap extended more than the other, you would have a different lift force on each wing, resulting in one wing being higher than the other. Would additional thrust on the opposing engine be used? Or is assymetrical thrust not a serious matter? What causes this condition-- hydraulic problem?

Thanks for any information.

Active loading only, ma'am, keep it moving!
4 replies: All unread, jump to last
User currently offlineRendezvous From New Zealand, joined May 2001, 543 posts, RR: 0
Reply 1, posted (6 years 10 months 1 week 5 days 23 hours ago) and read 4968 times:

Having one side with more flap means more lift on that side, and also more drag. The asymmetric lift would have to be countered with aileron. The asymmetric drag would cause the aircraft to yaw to the left or the right, and this is countered with the rudder.

Depending on the degree of asymmetry, it can be a pretty serious problem. You have to be able to apply enough control deflection to counter the asymmetry.

User currently offlineTristarSteve From Sweden, joined Nov 2005, 4354 posts, RR: 33
Reply 2, posted (6 years 10 months 1 week 5 days 15 hours ago) and read 4873 times:

Asymmetric flaps is very serious. Just compare the area of the flaps to the area of the ailerons and you can see that it would not take much asymmetric flap for the ailerons to be overpowered. So airliners have devices to stop it.
The usual flap motor drives a single torque tube that runs across the aircraft driving all the flaps. At the wingtips are rotary transducers that measure the movement. Any discrepancy, and the flap motor stops. Sometimes there are also brakes at the wingtips that lock on. This cannot be reset in flight. The crew will get an Asymmetric flap, or flap locked message. There are quite often also no back brakes on the individual flap drives.
All this is done to avoid asymmetry.

Now a story. We had just completed a B737-200 D check, and the aircraft went out on a manual reversion test flight. The pilot could not stall the aircraft as the left wing was dropping before he could slow to the stall. We adjusted one side of the flaps IIRC it was one turn of the flap drive tube (that turns about 250 turns flaps up to down). Problem solved.
I have seen many reports of Flap asymmetry recordrd in the log book, but never seen a real one. The flaps had always locked up.

User currently offlineBoeing767mech From United States of America, joined Dec 2000, 1037 posts, RR: 2
Reply 3, posted (6 years 10 months 1 week 5 days 14 hours ago) and read 4852 times:

Quoting RNOcommctr (Thread starter):
We had an Alert II here at RNO with an AA 757 landing with assymetrical flaps. The aircraft landed safely although it looked slightly crabbed on touch-down.

N622AA on flight 1933, that was a indication problem. The airplane was turned with only a 29 minute delay.


[Edited 2009-07-19 03:43:53]

Never under-estimate the predictably of stupidty
User currently offlineDufo From Slovenia, joined May 1999, 846 posts, RR: 4
Reply 4, posted (6 years 10 months 1 week 5 days 4 hours ago) and read 4753 times:

On embraer 120, flap assymetry is one of two things (the other is propeller overspeed) that can kill you if you don't react immediately. Luckily, some types have left and right sides mehanically interconnected to prevent such problems.

I seriously think I just creamed my pants without any influence from any outside variables.
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