In real world flap failure on a commercial airliner,are there redundant backup ways of lowering flaps -are there alternate electrical or mechanical devicesengineered into the aircraft.If not, how does one land?Peter Sydney Australia

On some aircraft, yes, there are alternate drive systems for the flaps. On other aircraft, no, there are not. A no flap landing can be made. The approach speeds are just higher.

I don't know of any commercial aircraft with an alternate drive mechanism, although a number do have an alternate control mechanism.A no-flap landing is no big deal as long as it's done lightweight and on a long and preferably dry runway. I've done no-flap practice landings in most of the transport category jets I've flown.RegardsBob ScottATP IMEL Gulfstream II-III-IV-VSantiago de Chile

>I don't know of any commercial aircraft with an alternate>drive mechanism, although a number do have an alternate>control mechanism.quite correct. the alternate control is simply if the flap handle breaks off.>A no-flap landing is no big deal as long as it's done>lightweight and on a long and preferably dry runway. I've>done no-flap practice landings in most of the transport>category jets I've flown.true again. a no flaps approach and landing is part of the CA's type ride. usually expect about 50-60% increase in the expected rollout (without reversers would add about 25% more).

There are two issues here, Flap commanding and Flap operation. In a fly by wire aircraft, this allows the possability of multiple electronic cable runs in seperate locations reducing the risk that a single physical failure [ e.g. a small bomb ] will disable the Flap commanding function, the Flap operation function is assured to the highest possible level by having multiple hydraulic systems. All in all this is not a big issue, since a total flap failure in a commercial airliner would have no more serious effect than a resulting requirement to land at a faster speed, than could be achieved if flaps were available. The big problem in a large airliner would be loss of function on control surfaces in that would leave the flight crew with differntial thrust from the engines as the only way to retain some degree of flight stability and directional capability. http://yarchive.net/air/airliners/dc10_sioux_city.htmlBest and Warm RegardsAdrian Wainer

747-400 flaps have both a primary and alternate drive system. If the primary hydraulic system is inop, there is a backup electrically driven drive system for alternate flap deployment. And 737s have a similar system as well.

Thanks all, for your very kind & informative responses.That's exactly the info I wanted.Sometimes you hear of incidents around the world & youwonder what the proper procedures are.Thanks again.Peter Sydney Australia

G'day Peter,Most modern commercial airliners (Boeings) have mechanical torque tubes, extending from a gearbox in the wheel well, that drive thru angle gearboxes and Saginaw jackscrew actuators to extend the trailing edge flaps. The gearbox in the wheel well has 2 power sources. The primary source is a hydraulic motor ( controlled by the flap handle) and the secondary (emergency) source is an electric motor (controlled by guarded switches on the pilots overhead panel).Thus if its a power source problem then the alternate power source can be used but if anything goes wrong with the mechanical drive mechanism then there is nothing the crew can do.. as soon as assymetric flap is detected the flaps will automatically stop functioning and the pilot will have to land the aircraft as best he can.Cheers,Roger

Thanks Roger.Peter Sydney Australia

>Thus if its a power source problem then the alternate power>source can be used but if anything goes wrong with the>mechanical drive mechanism then there is nothing the crew can>do.. as soon as assymetric flap is detected the flaps will>automatically stop functioning and the pilot will have to>land the aircraft as best he can.Unless the assymetric flap protection mechanism fail as well, in which case the results of assymetric flaps may lead to dangerous results!I personally witnessed such case in a 757 that had arrived in Athens one night back in 1993 (or 94). I was working as the airline supervisor then, and while waiting for the a/c to park I noticed the left wing flaps still at landing position while the right wing flaps were retracted. Rushed into the cockpit, informed the captain, checked the flap gauge, both needles showed 'UP'.The aircraft departed 8 days later after Boeing had sent special crew to examine why the assymetric protection failed and the aircraft was repaired.Good thing it was a very nice calm night and the aircraft did not need to perform a go-around for some reason. I can't think of what could happen during the go-around when the crew selected flaps 15...I think I still have some photos of the repair process.George DorkofikisAthens, Hellashttp://online.vatsimindicators.net/811520/1704.png