generator drive switch

[goksunkurkcu]

during my line training i'va had many questions from my teachers, but the ones that is not on the books are he hardest. can anyone tell me why are the drive and alternate flaps switches are colored red?

[dream747]

One notable fact is that extending the flaps using alternate power is a irreversible thing inflight. You will not be able to retract them again in the air.

[SNS3Guppy]

One notable fact is that extending the flaps using alternate power is a irreversible thing inflight. You will not be able to retract them again in the air.


In what aircraft?

In aircraft I've flown with an alternate means of operating leading edge and trailing edge flaps or devices, (the question and the replies thus far don't state which), the device can be extended and retracted under alternate power.

As Dream747...the flaps when operated under alternate power (electric motors) in the 747...can be extended and retracted in flight, and on the ground. Same for the leading edge devices. I the case of the leading edge devices, arming the system permits continued operation using pneumatic crossbody bleed air, and when the alternate leading edge switches are used, the bleed is bypassed for the use of electrical power. In the case of the trailing edge flaps, arming the alternate switches disables the hydraulics by putting them into bypass, until the arm switches are shut off. When the arm switches are shut off, the hydraulic operation of the flaps resumes. If the hydraulics for the trailing edge are left in bypass, the flaps may be raised and lowered using the electric motors controlled through the alternate trailing edge flap switches.

This brings up the obvious...when one asks a question such as "why is the switch red?" this leads one to wonder which aircraft it is to which the speaker is referring. Of hundreds of airplanes and tens of thousands of switches an switch combinations, one might be a little more specific.

[MarkerInbound]

While in the 727 the trailing edge flaps could be extended and retracted by the alternate electric motors but if you used the standby hydraulic system to extend the LEDs, they have to stay extended unless you can go back to the normal system.

[dream747]

Apologies for my mistake. I went to read up and refresh; they can be retracted again after extension. My bad!

Guppy, as a side question, what happens if you extend the flaps normally on a routine approach and on one wing it doesn't extend to the degree as commanded resulting in asymmetric drag? Is it possible extend it to the commanded degree by switching to alternate power without affecting the wing that is operating normally?

[bcgallacher]

Flaps will not extend differently on each side as assymetry protection systems will lock them out, on Classic 747 there is no assymetry protection with the alternate electrical system so it is not a permitted procedure to operate the system after an assymetry trip. One flap drive unit operates inboard flaps while a second operates the outboard so it is possible to have a failure of one system in which case the alternate drive system may be used.The assymetry protection system uses the cockpit flap indicator - split pointers trigger the trip.

[Coldbear]

The IDG is guarded because it's, as others pointet out, irreversable. The drive can ONLY be reconnected on the ground, with the engines stopped, because a mech guy has to do it.

Martin

[flyburg]

It's to late to look it up but on the B737 on the flaps, I think when using the alternate system, you can extend and retract the flaps but not the leading edge devices. That would make it irrevisible just as the CSD.