Hi BOAC. It's the stall warning. The Airbus Flight Crew Operating Manual 3 defines the point at which recovery should be made, the new procedures are an amendment to the current procedures and deal purely with the recovery actions. However, you will only get a stall warning in a reversion flight control modes.
The FBW Airbus will normally be flying in Normal Law where stalling is theoretically impossible. The protections will not let you do it. If there are flight computer degradations or an upset which has not been prevented by the normal protections, then you may be in Alternate Law. If you lose more computers or ADCs, then you may be in Direct Law which means that the control surface deflection is proportional to stick movement - i.e. like a conventional aircraft. The aircraft can be stalled in Alternate or Direct Law, but there is a very definate stall warning associated with his. In Normal and Alternate law, the aircraft will not pitch up with power application. Only in Direct law.
So the instances where these new memory items may be required will be very rare. I have never been out of normal law in 4000hrs of Airbus flying. My company has a fleet of 30+ and we have had one case of Direct law in the last 5 years - casued by a double RAD ALT failure where the aircraft reverts to Direct Law when the gear is lowered.
And as for the new procedure, I suggest any pilot would apply a healthy dose of airmanship if required. I think if I was to stall at 200' on approach, I would use some power.
As for the use of ailerons, I don't remember exactly at what stage of the stall we used them down to while flying the Hawk- I will ask someone who has flown it more recently. As for the Airbus procedure, it's in the memory item procedure therefore, it is approved by the manufacturer. Perhaps it's because in Alternate and Direct law that VSW (Velocity Stall Warning) is somewhat higher than the actual stall speed and the ailerons are still safe to use and limiting the load factor by reducing the angle of bank is the main priority.
I'm in agreement about the different characteristics of swept wing stalling. Earlier types tended to pitch up as the tips stalled first and the centre of pressure moved forwards. Two of my previous types exhibited this trend (Victor and VC10) and as both had T tails, this was definately not a good thing! Some other types exhibit a classic nose down pitch. The B747 was originally designed with no stall warning or protection at all. It was only the British ARB which demanded a warning system which led to a stick shaker being fitted. Which is why the B747's device looks like an afterthought - an electric motor with an eccentric weight attached, and clamped to the control column.
The VC10 has a duplicated shaker and warning system. The pusher actuates before the stall and the system has a 'rate computer' which takes a feed from the AoA sensor and triggers the system earlier if there is a nose up pitch detected. The Victor had no stall recovery aids - except for deploying the brake chute in the vague hope it would pitch the nose down before the weak link broke. More than one Victor met it's demise in stalling.
Last edited by Dan Winterland; 24th Jul 2010 at 17:52.