Flaps Asimmetry

[L'Argonauta]

Does it happen more often during extension or retraction?

[bookworm]

Depends on the nature of the systems. One would hope that with modern transport category aircraft it happens rarely if at all!

With some of the older Piper light aircraft like the Comanche, retraction is by spring forces pulling the flaps up against air loads. Friction in the system can cause an asymmetric retraction, which is somewhat exciting but usually quite controllable. Re-extending flaps and retracting at lower speed to reduce the air loads seems to do the trick.

[Jumbo Driver]

In my experience, it has tended to happen much more frequently in the simulator than in the aircraft, for some reason ...


JD

[James02]

I can only remember one incident that a 747-400 performed a landing with flap assymetry. It happens indeed more frequent on the simulator than in real-life.

[dixi188]

Once had an Assym. and that was on extension on the ground while taxiing for take off. Lockheed L188 Electra. Caused by failure of screwjack nut.

Just remebered another one on Electra caused by a very firm landing, I think one of the detection micro-switches bounced.

Had several Slat and Flap Jams but no Assym. on A300 caused by water ingress in screwjacks and freezing in flight, hence won't extend. Usually cleared by flying around at low level for a while, but not always.

Hope this helps.

[Checkboard]

My company has had a couple of these a year, for several years - mostly caused by corrosion problems in the flap asymmetry contact switch - and indeed happens much more on extension than retraction.

[421dog]

Had one many years ago on approach in IMC in a C402. An actuator cable broke on one side and the chain came off of the sprocket. Flaps would not do anything but go down more on one side.


It was pretty... entertaining, and we scattered check boxes and fedex overload around the cabin a bit before we got it on the ground.

[Flight Detent]

Uh! I don't understand your last comment.

[CaptainSandL]

On the 737 it (assym, skew, disagree etc) happens far more often on extension than retraction. Maybe it is because the airloads are higher during extension.

[Swedish Steve]

Does it happen more often during extension or retraction?

The question is does flap asymmetry occur. My answer is that in 40 years on airliners I have never seen flap asymmetry. I have seen plenty of times where the flap asymmetry detection system operates and shuts down the flap motor and applies the brakes and puts up a flap asym message, but it has always been indication to me. I can recall one slat asymmetry where aa gearbox sheared on a B767, but no flaps.
The flap asym brake system is so good on airliners because the effects of real flap asymmetry are so great.

[Bullethead]

G'day Gents,

I've had two flap asymmetry events in over 35 years of flying both on B767s. One was a spurious warning and the system behaved as advertised and locked up, the other was a real failure of the torque drive tube to the outboard three sections of LE slats. In this instance the asymmetric override protection function failed and the LE devices went completely asymmetric with three quarters fully extending and the busted bits only just leaving the fully retracted stops.

Interestingly there was little adverse roll tendency. We weren't even aware that the protection function had failed and that the slats were actually asymmetric until after the aircraft was parked and shutdown.

Engineering investigation failed to reveal why the protection function didn't activate.

Regards,
BH.