Windshear and takeoff flaps settings

[bluehawaii]

In a twin engine jet aircraft with flap 7 or 15 setting configuration option. How does either flaps 7 or flaps 15 setting affect wind shear escape maneuver?

[Capt Claret]

In practical terms, I don't think it does. The procedure on the Douglas/Boeing 717 is pitch to the PLI (Pitch Limit Indicator - onset of stickshaker), max power, emergency max power if required, and, DO NOT RECONFIGURE until clear of shear.

In real terms, it is most likely that Flap 7 (I assume you means degrees?) will provide better climb performance than flap 15, assuming all other variables are constant but the manoeuvre would be flown the same way for either flap setting.

[bluehawaii]

Thanks Capt Claret,does this have any relationship to second segment climb performance?

[Capt Claret]

does this have any relationship to second segment climb performance?

Only in that generally, second segment will be better the less flap that one has, but one might need a higher flap setting to carry the better load off the available runway. It's a compromise. The 717 has a requirement for minimum of 5 degrees of flap for takeoff, and a variable flap selector that allows anything up to 20 degrees for takeoff.

Whereas my understanding of windshear escape is that all segments go out the window, and one uses all available power, and the highest AoA possible - without stalling of course to out climb a severe downdraught. Fortunately my experience to date is limited to simulator models, and I hope it stays that way. :}

[bluehawaii]

Capt Claret, I agree with you entirely. Second segment is not a consideration in an all engine escape maneuver. Thanks for your time and information.

[Intruder]

In practical terms, flap setting DOES have a bearing on performance!

In the 747, the choice of using Flaps 10 or 20 for takeoff has to balance takeoff roll performance (better at Flaps 20) with climb performance (better at Flaps 10). While the 744 usually has plenty of excess thrust available, it is not the case with the 747 Classic. I have been in a situation where Flaps 20 was needed for runway limitations, but the airplane would not climb above 2000' until the flaps were retracted to 10. If you add windshear to that situation, it is clear that Flaps 20 would significantly detract from climb ability, possibly making recovery impossible.

The obvious answer is to not attempt takeoff when there is known low-level windshear. Also, do not attempt takeoff in marginal conditions when windshear is suspected or forecast. If you decide to risk it, optimize for climb performance, because that is where it will be most needed.

[Cough]

Whatever flap setting you go with, using an improved V2 climb will also help matters..

[de facto]

Cough Whatever flap setting you go with, using an improved V2 climb will also help matters..


Cough cough:suspect::ooh:

[GlueBall]

Practical reality suggests that if you can get off the pavement at flaps 10, then there is no need to use flaps 20 . . . because once you're airborne, flaps 20 is unnecessary drag during climb, and especially in case of an engine failure. :ooh:

[bluehawaii]

Good points, so the lowest takeoff flaps setting is the best setting in the event of a low level windshear encounter immediately after takeoff. Though we never depart with windshear reported in the vicinity of the airport. Thanks Ladies and Gennts.

[Natstrackalpha]

and, DO NOT RECONFIGURE until clear of shear.
*********************************************************

[Rick777]

Most FCOMs that I am familiar with have a recommended flap setting for possible wind shear=like if it is gusty but no wind shear actually reported.