Landing Gear Retraction??

[Snigs]

I'm currently involved in an FMEA on the A380 gear retraction systems and we're looking at inadvertent retraction scenarios.

What I'd like to ask is: What are the criteria for the PF calling "gear up"? Is it as simple as just positive rate of climb or is there a particular speed to be reached before gear up is selected (e.g 1.2*V2 or similar)?

[A-V-8R]

Me thinks it depends on the airplane....

Little Airplanes we used to use positive rate of climb/gear up callout....

Some airplanes on rotation show a false rate of climb indication - the B 737-200 that I flew many years ago would show up or down on rotation....

And on the 777-200 I'm on now it is so long that if you pull the gear up on the positive rate of climb during rotation the mains are still on the runway! Most people at my airline wait to hear the Autobrakes snap off before calling "gear up.."

[BRAKES HOT]

In my airline we must have both positive rate of climb and increasing rad. alt. readings before retracting the gear. hope this helps

[Snigs]

Yes thanks for that.

The problem we're working through is a failure of the hydraulic valve which pressurises the system to retract the gear, whilst on the ground. The retraction of the body landing gear before airborne (nose wheel up, weight coming off the MLG) would be catastrophic (nose down rapidly, leading to NLG failure).

Hence, we need an isolation valve in the system. Thus this isolation valve will need to give authority back to the main hydraulic system from between the wheels leaving the ground and gear selection up, which judging by your replies, this isn't a long time.

The valve that operates the emergency extension (gravity fall) could be used but is (as you've pointed out) way too slow.

A-V-8R I presume that the autobrakes "snap off" after the weight on wheels switch is deactivated!?

[Snigs]

I guess BRAKES HOT SOP's are pretty standard. Any one out there with significantly different procedures?

[411A]

VSI/IVSI are, at times, unreliable.

Rad Alt is likewise for a very good reason, sloping terrain.

The only really reliable indication for a positive rate of climb is....a positive sustained climb indicated by the pressure altimeter.

Rad Alt and VSI/IVSI should be used in a support role only.

[BRAKES HOT]

actually the rad alt is an extremely reliable aid to use. If the autoland can trust it so can I! In most a/c it will be calibrated to the main gear anyway.

[411A]

Brakes Hot,

You of course realise that the rad alt is used for autolands over a predetermined surveyed surface. Should you depart from a runway, with the rotation and initial climb close to the end, the terrain may drop away rather quickly, leaving you with the rad alt indication of a sustained climb when in fact the aircraft may well be doing quite the opposite.

Those that have been flying heavy jets for a long time realize this, and act accordingly.