Alternate Flap Extension - B767

[BarrowBoy]

Can anyone explain why during Alternate Flap Extension on the 767 the following point is stated as part of the QRH drill?

If flap lever is UP:
Flap lever . . . . . . . . . . . . . . . . . . . . . . . . . 1
This prevents uncommanded autothrottle
disengagement.


Cannot understand why the lever at Posn 1 stops uncommanded A/T disengagement.

Thx BarrowBoy

[NSEU]

My notes don't quite hit the mark on this, but... for info...

When the flaps are set to the 1 detent, the thrust management computer estimates the slats moving to the flaps 1 position linearly in 5 seconds. There is a microswitch on the thrust lever assembly specifically for this.

Flap position is used to generate max speeds in EPR/N1 ref mode, but this seems to be more general.

During approach, Go-Around Mode will not be armed (if the flaps are not greater than zero).,.. unless glideslope is captured.

With flaps extended, Min Spd is defined as 1.3Vstall. With flaps up, a stall margin is provided such that a 0.5g pitch up maneuver can be performed.

There seems to be quite a range of things which are different with flaps up/not up.

I could understand why flap position is important, and how a failure of the Flaps 1 switch would cause disengagement, but not why the A/T would disengage if the flaps are not in the 1 detent (perhaps the A/T computer is smart enough to know that the TE flaps are moving, but the flap 1 position has not been activated.... and assumes a failure of the flap 1 switch?)

Rgds.
NSEU

[gimmesumvalium]

As background, the previous procedure generally resulted in the Autothrottle tripping off, resulting in increased workload. They (operators) found that by following this new procedure, the Autothrottle would not trip off, resulting in reduced workload. Boeing then approved this checklist.
Positions of sensors, micro-switches, etc would best be left to SpannerTurner for explanation.