Gear downlock override.

[FIRESYSOK]

Does anyone have opinion on the use of the downlock override mechanism present on most A/C? I can't find mention of it in any QRH or normal procedures.

My question is- would it be prudent to use if the landing gear did not want to retract? Or only in an engine-out situation. My thinking is to return to land, leaving it down rather than risk further gear problems forcing it up.

Thanks-

[Oktas8]

I have no practical experience with such aircraft, but I have a brief comment that may perhaps be helpful.

That said, (and if I've understood you correctly), the E110 Bandeirante flight manual suggests that this mechanism is to be used to raise the gear on the ground in an emergency, and will cause major damage to the undercarriage system.

The E110 was designed with military applications in mind, and in some cases it may be better to raise the gear during the landing roll than slide off the end of the too-short strip - eg if there's a cliff at the end...

[Captain Stable]

Put simply, you'd use it if you urgently, desperately needed to get the gear up; for example, to get over that big lump of rock when you've suffered a failed donk and the gear likes letting it all hang loose.

Any other situation, yes, you'd probably wander around to the other end and place the wheels nicely on the hard bit of tarmac they thoughtfully placed there for such eventualities.

I once used it in the sim when still on the runway. (The gear lever lock works quite nicely with weight on wheels! :D ). We had an engine out, but I had convinced myself we were airborne, so I hit the override. The gear came up - and we carried on flying, at about 4' QFE! Gradually climbed away - afterwards the TC said "I REALLY don't know how you pulled that one off!".

Nor did we. ;)

[Kotare]

I investigated an accident where a downlock override was used. The pilot lost braking coming into the line and rather than plow into the military terminal, hit the override and selected gear up at the same time pulling the idle cutouts. The DH Devon slid gracefully to a halt in front of the waiting passengers. Damaged both props, belly skin and the pilot's career.

[Fresca]

It is in the QRH of both the 737-Classic (300-500) and the 757.

If the gearhandl will not move after T7O there is some procedure to follow on the 737, which can lead to return to a suitable airfield (if I remember it correctly). On the 75 however it is just: press the button, move the handle, procede normally.

This difference is I beleve due to the 737 uses squat switch in the R-H main gear for air/ground sensing, but the 757 uses bogie tilt; when the gear enters the wheel well it will tilt and the aircraft goes into airmode

[411A]

If the bogie is not in the correct position, damage to the wheel well/doors can occur or the gear can become jammed in the well...not good in either case.
On the B707, the override was called the '30 day trigger'...use it without good cause resulted in 30 days off without pay.

[Elliot Moose]

The lock mechanism itself is obviously there as an idiot switch--to prevent accidental retraction on the ground (ala Homer Simpson:D ) If however, it is possible that the microswitch will fail to release the lock as weight comes off wheels. This used to happen to us on one B200 when the weather got down around -40 ish. So we would just pull the release out manually, and continue on our merry way. It seems to me we had a 748 that tended to do the same thing. It just meant that you had to use two hands to pull up the gear.

[Fresca]

411A.

If the bogie is not in the correct position, damage to the wheel well/doors can occur or the gear can become jammed in the well...not good in either case.

The 757 has a mechanism that tilts the bogie when it enters the wheelwell if it fails to tilt by it self. Therefore no damage wil occure to either the wheel well nor its doors, and as the gear has the correct tilt it will not be jammed in the well. As for landing: At touchdown the gear will de-tilt and then the aricraft enters ground mode again.

Ergo: No problem using the override switch

Pretty clever huh?

[renard]

On the Jetstream41, the flight manual says that the undercarraige override button must only be used when you are in danger of ground contact e.g. enginge faliure and the gear hasn't come up and you're not climbing that well.


I think that if the gear didn't come up, I would leave it down, subject to the example above. If you did use the override and then the gear didn't come down, the subsequent "tea and biscuits" could be very uncomfortable.