777 Windshear recovery

[wilco77]

Manual Flight recovery procedure:
-Disengage auto pilot
-TOGA
-apply max thrust
-disconnect auto throttles
-roll wings level pitch to 15 degrees
-retract speed brakes
-follow fd.

my question is what is the reason we have to disconnect auto throttles.

[STBYRUD]

To prevent the thrust levers from being retarded if for example the AFDS captures a target altitude and thus changes the thrust mode to SPD.

[flapsupdown]

STBYRUD:

Then why for windshear recovery with the autopilot in do we not disconnect the A/T? Surely, when ALT captures with the autopilot in, the thrust levers are going to retard to give SPD

[STBYRUD]

Yes, but the difference is that the autopilot will actually fly the leveloff if you reach the MCP altitude, if you handfly your recovery you might have different plans than to stay at low level and don't want thrust taken away from you in any case. Regardless-up until the 777 it used to be Boeing procedure anyway to disconnect the autothrottles whenever flying without autopilot, this could be the last remainder of that previously ubiquitous rule...

[Tee Emm]

it used to be Boeing procedure anyway to disconnect the autothrottles whenever flying without autopilot.

It still is Boeing policy in the 737 series except during take off and climb in either automatic or manual flight. A sound policy too.

[flapsupdown]

Thanks STBYRUD

[STBYRUD]

Couldn't agree more, Tee Emm, I don't like that it changed... If that was the rule on the 777 as well I very much doubt the Asiana accident would have taken place as it did.

[PW1830]

Wilco,
The 747 windshear escape manoeuvre, with the windshear warning system, is as you state except "rotate TOWARD an initial pitch attitude of 15deg" and follow F/D guidance.

Subtle difference but in extreme cases 15deg will lead to stall.

[FCeng84]

Autothrottle during Manual Flight

One of the main reasons for disengaging the autothrottle when flying manually is the workload associated with having to re-trim pitch each time that the thrust setting is changed. This is the case on an airplane without FBW pitch control augmentation that has under-slung engines.

On the B777 and B787 the FBW augmentation provided in the pitch axis during manual control (C*U) does such a good job of adjusting the elevator to account for thrust pitching moment changes this is no longer a problem. The autothrottle helps greatly with maintaining speed so that benefit is preserved by keeping it engaged.

[wilco77]

Thanks So much guys. Clears my head to that question I have always pondered upon..

[ANCPER]

Flew for an operator (733) that didn't follow that rule of AP off, AT off and it wasn't a problem, and neither was trimming the a/c with the AT on and AP off!