Airbus question

[Doors to Automatic]

Having travelled on BMI's new A330 recently I have a couple of questions about the airbus auto-brake system.

Am I right in assuming that reverse thrust has no effect on the stopping distance when Autobrakes are set but merely transfers some of the braking effort away from the brakes when selected?

Secondly at say typical landing weight on an A320 what is the difference in stopping distance between the Low, Medium and Max settings?

Any info appreciated as always.

[SLT]

Hi

The use of the reverse thrust will sometimes have an effect on the landing distance when used, either with or without the autobrake system. It can reduce landing distance by as much as 4% at typical landing weight on an A320, in normal conditions, when used with Autobrake Low. It can be much more in for instance slushy or icy conditions, up to 26% in the icy case!. Reverse has very little effect on landing distance when used with Autobrake Medium, on a dry or wet runway. Reverse thrust is not taken into consideration for landing performance figures.

Second, at a typical weight of 60 tonnes, the following are the figures for Actual landing distances (Config Full, ie. Full Flap/Slat) :

(Assuming runway dry, normal C of G, sea level airfield, no reversers operative, and no tailwind component)

Autobrake Medium - 1250 metres
Autobrake Low - 1840 metres
Autobrake Max - 830 metres (at 62 tonnes)

Use of Autobrake Max is not recommended for landing, as it applies Max braking immediately the main wheels are down. This could result in the nose coming down very hard, with subsequent damage to the nosegear, especially on A330/340, as the nose is a long way up on landing. Autobrake Medium applies 2 seconds after main gear touchdown, and Low after a 4 second delay.

All info from FCOM 2.

Hope this helps!!

[wonderbusdriver]

The autobrakes in min or med select a certain deceleration (!!) of the aircraft.(don´t remember about max - full brake press is probably correct).

So, yes, if the pilots use reverse, the brakes themselves have to work less depending on the amount and amount/effectiveness of reverse. (same on MD11 actually, as I´m just learning).

Among other positive factors, use of autobrake reduces the wear on carbon brakes much less also, since they have a better temp for braking during taxi.

It also causes them to be used more "equally" than with manual e.g "foot" braking.- "car-driver-syndrome".

[Doors to Automatic]

Many thanks for the info. When we landed at O'Hare the brakes appeared to apply quite hard but I distinctly remember a 2 second gap so I guess it must have been medium!

[F/O Junior]

SLT, don't mix the system of the A320 and the A330. All decelereation times given by you are only valid for the A32x.
On the A330 on the other hand, Automatic Braking is activated by the ground spoiler extension command. In addition for MAX mode, the nose landing gear compressed signal is required. This avoids the hard landing of the nose wheel.

[SLT]

Junior,

If you read my post again, you will see that I did in fact say that all those landing distances are for A320 - which was what was asked for. So I'm not mixing the systems. The A320 family is the same as the A330 for autobrake activation - ground spoiler extension. I described it as main landing gear touchdown - not wanting to get too technical for someone who doesn't fly the a/c. Sorry.

I didn't know that about the A330 in MAX A/BRK - thanks for that.

[Flap 5]

In my experience on the A330 we would use Low Autobrake, Medium would be a bit too abrupt.

On the A320 we would use Medium. With Low on the A320 it would be close to max reverse which would mean the brakes cutting in and out (as the autobrake works on a constant rate of deceleration), thus leading to more brake wear.

[Doors to Automatic]

The braking was rather abrupt (we were in an A330) and the ground run was in the order of 4500 feet (1400m)

[Flap 5]

That would seem to equate to Autobrake Med or heavy boots!