Because of the high buildings around London City an approach needs to be done at 5 degrees rather than the normal 3 of most airports.
Airbus has fitted a special "steep descent mode" button to the two A318s which configures the flight control computers to achieve this. If you notice the spoliers automatically retract at the same time the 'retard' call is made in the cockpit (entry into the flare).
If a go-around is needed the spoilers will also automatically retract when the thrust levers are pushed to TOGA (take-off/go-around power).
Originally Posted by PPRuNe
Airbus have managed to achieve this "steep approach" capability for the A318 essentially by special programming of the Fly-by-wire Flight Control System. To achieve a speed-stabilised steep approach (and to demonstrate this at even steeper approach angles than the LCY glideslope), some of the speedbrake panels are partially extended during the approach. This reduces lift and so Vref is increased (to Vls+8 kts). It seems that lots of things happen behind the scenes with the control computers, including changes to the gains in the autothrottle, AOA protection, roll authority and flare laws.
However, Airbus claim to have made it as straightforward as possible for the crew. Evidently additional simulator training is required at Toulouse, and the aircraft monitors all of the various mode selections and modified control laws [as I understand it, in a similar manner to the "autoland" warning function, ...any malfunction leading to a mandatory go-around (unless there are mitigating circumstances, eg a fire). Standard call out heights are substantially modified as are rules for GPWS activation, etc, due to higher rates of descent.
The interesting bit as I recall is the flare, as retracting the spoilers would cause a float and leaving them extended makes for a bit of a firm arrival, so there is some sort of compromise where they are retracted from 30 degrees to a lesser angle, and of course all fully deployed as usual after touchdown. The flare is initiated much higher than normal, due to the steeper approach angle and higher rate of descent.
So there are modified SOPs and some new skills involved, though I think I read that the steep approach, once armed and activated, can still be "hand-flown", Airbus-stylee, using the "bird" (Track/Flight Path Angle selected on Primary Flight Display). I remain mightily impressed by the capabilities of the airbus FBW aircraft, and the A318 (together with the new Embraers) will surely open up new possibilities from LCY and new sales for an aircraft that, hitherto, didn't really have an unique selling point.
Glad you enjoyed BA004...it's a great service.