Configuration change during Windshear recovery

[Hachiouji-shi]

From the QRH, the windshear recovery maneuvre prohibits changing GEAR and flap configurations. Why?

Retracting the gear results in less drag and hence better climb performance?

[mong`s]

This is true. however you have to get the gear up first and that means opening the gear doors. ie more drag in a critical phase of flight.

[JW411]

Apart from which having the gear down would be quite beneficial if you are unfortunate enough to hit the ground during the process of recovery!

[FougaMagister]

...er, depends what aircraft we're talking about. While I agree that QRH/SOPs require NO config change during windshear recovery, on some planes (ATR for example) the main gear doors are open when the gear is down, hence the extra drag would only come from the operation (opening, then closing) of the nosewheel's two half-gear doors... quite a limited temporary drag increase really, but still let's stick to SOPs!

Cheers :cool:

[Hachiouji-shi]

What is the relationship between changing GEAR and FLAP configurations and Stall qualities etc? I swear I came across this somewhere sometime.

[Old Smokey]

GEAR - If you've taken the aircraft all the way to the thrust and pitch limits, but descent still continues, you are INFINITELY better off in the ground impact with the Gear extended to absorb all or much of the impact load. Of secondary importance is the drag rise with some aircraft which open the gear doors during retraction. Bear in mind that for those aircraft that do not experience a drag rise during retraction, it still extracts power from the engines to operate the Hydraulic or Electrical systems to do so. Aircraft with Pneumatically operated gear retraction (becoming a rarity) would be the only exception (Even then the compressers will extract power to top up the pneumatic accumulator as the pressure is used).

FLAPS - Flap retraction would cause lift loss, thus making the sink rate even worse. There may be some merit as a discussion point in selecting the next stage of flap if stall is imminent and sink rate continues. It would be a short term 'fix', as drag would consequently increase, BUT, there are recorded cases of pilots in a performance limiting situation when impact was imminent in taking an extra stage of flap to delay the stall. The 'Increasing Flap' argument is obviously of no relevance during landing, when, in all probability, Full Flap is already being used.

Regards,

Old Smokey

[alf5071h]

GEAR ... you are INFINITELY better off in the ground impact with the Gear extended to absorb all or much of the impact load.
Windshear – an example of a successful recovery – the crew followed SOPs (www.fly-safely.org/story.asp?id=32)