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pudd
27th Sep 2004, 18:43
Anyone know why the A330 stays in alternate law not direct law when putting the gear down? (autopilot off)

catchup
27th Sep 2004, 19:18
Isn't it a normal procedure, even for the A330, to put the gear down before landing?

regards

Capt. Inop
27th Sep 2004, 23:45
Isn't it a normal procedure, even for the A330, to put the gear down before landing?

Yes it is, takes too much power taxiing to gate with gear up :}

Cripple
28th Sep 2004, 11:48
The A330 does stay in Alternate Law after selecting Gear Down.

The Flare Mode engages at 100' RA (as it does in normal law), where pitch trim is frozen and the sidestick pitch demand is proportional to elevator deflection (as in Direct Law). Roll however is still in Alternate Law (sidestick commanding a roll rate) with or without Bank Angle protection depending on ALT 1 or 2.

The aircraft is therfore in Alternate Law Flare Mode, which is not dissimilar to Normal Law Flare Mode (where pitch is direct but roll normal below 100'RA).

I think the confusion comes from the fact that the A320 series has a more complex Normal Law Flare Mode, involving memorising the attitude at 50' RA and then inducing a nose down trim that the pilot has to Flare against, simulating a "conventional" Flare. This calculation is quite complex, and therefore Flare Mode is not available in Alternate Law on the A320. The control Laws revert to Direct Law (in Pitch and Roll) on selection of Gear Down to allow the pilot to Flare the aircraft in a conventional manner.

There is a similar difference between the A320 and A330 in the event of a dual RA fault. In this case the absence of RA information prevents the computers from calculating when to engage flare mode. As someone has already pointed out, it is usually SOP to select Gear Down before Landing. So, with a dual RA fault, Gear Down causes transition from Normal Law to Direct Law on the A320, but from Normal Law Flight Mode to Normal Law Flare Mode (pitch direct but roll normal) on the A330.

Hope this helps.

FD Standby
28th Sep 2004, 12:43
I only fly the minibus - but I think Pudd is refering the the fact that when in alternate law, and you drop the gear - the small bus reverts to direct law.

pudd
1st Oct 2004, 15:49
Silberfuchs RTFQ!! I am well aware of flight control laws but thanks for the tongue in cheek answer anyway! Cripple, many thanks for the in depth answer which I was looking for. Fd standby,yes I was comparing the 320 to the 330 in this situation, Happy flying Pudd.