Autobrake Disengaging

[AirbusTEch]

Hi Folks !
On the Airbusses :
Is there a difference in "Brakepedal Deflection Angle" if you disengage the Autobrake System at different levels ? ( i.e. LOW MED or MAX )

[mono]

From my training notes it is not clear if more pressure is required for different auto brake levels. I would assume not.

What my notes do say however, is that for MAX autobrake disarming BOTH pedals must be pressed, but for LOW/MED only one pedal need be pressed.

[dvt]

Looking for a smooth way to disengage autobrakes? This works on Boeings, I'm sure the same principle is at work on the "cheap Boeing imitations" as well.

Move the spoiler handle forward about an inch, forward and back quickly. Not full forward, just an inch. The autobrakes gently pop off because the airplanes thinks you're going around.

[MasterGreen]

Opinion Time :

Disengaging AutoBrakes using the 'backdoor method' of cycling the speedbrake lever 'an inch or two' is not a good idea or airmanship. Reasons are :

1. It takes the brakes from ON to OFF instantly. Lurches the aircraft forward and stresses the systems.

2. The loss of Speedbrake surface deployment - albeit momentary and small - reduces their braking effect and more importantly, the lift dumping. This could be a problem if the runway remaining is marginal or if the tyres are at their adhesion limit in a crosswind.

3. Rather like premature retraction of flaps on the landing roll. Why cycle a hydraulic system and risk a problem at such a critical phase.

4. Not a manufacturer's approved method.

The best and controlled way to disconnect the autobrake is to apply sufficient braking pressure via the foot motors to overtake that (pressure) being applied by the maxerette / autobrake system. This will provide a smooth transition to freewheel as you reduce foot motor pressure and minimal stress on the systems (hydraulic and gear struts). Stow the speedbrakes when the landing is complete and down to taxi speeds (after the high speed turnoff for the pedantic !). Likewise retract flaps after the speedbrakes. Then, should there be any hydraulic line damage due to whatever on the final phases of your now successful flight, you will be in the best position to deal with the subsequent loss of other services.

Local variations apply - but loss of nosewheel steering and main brakes have been recorded after speedbrake retraction / flap retraction on landing. Why get into bad habits when it really is a bad habit.

Discuss ....

MG