Disengaging autobrakes in the 737 Classic
 

I read an A330 incident report where the pilot during an abort tried to disengage the autobrake system which was on MAX (RTO in the 737?) by depressing the brake pedals. He had great difficulty doing so. The report stated that in the A330, the amount of pedal deflection required to disconnect the autobrakes from the MAX setting, is 2.5 times that required for disengaging the autobrakes from LOW setting.

Does that also apply to the Boeing 737 series because there is nothing I could find about that in the various manuals?

Why not simply stow the speed brakes?

Disengaging auto brakes with manual braking requires applying heavier manual braking than the auto brakes are applying. So it makes sense that the pedal deflection would be higher for higher auto brake settings.

For the classics, over the range of AB 1 to 2, there is no difference in the pedal pressure required to trip the auto brakes OFF. I don't know the exact number, but the trip pressure is somewhat lower than the lowest setting (1) brake pressure (1250psi).

To cancel the autobrake on the landing roll with toe brakes you must apply a brake pressure in excess of 800psi (ie less than that required for autobrake 1).

For the techies amongst us:

Autobrake Selector / Max Pressure at Brakes (PSI) / Deceleration Rate (ft/sec²)

1. 1 / 1250 / 4
2. 2 / 1500 / 5
3. 3 / 2000 / 7.2
4. Max / 3000 / 12 (below 80kts)
5. Max / 3000 / 14 (above 80kts)
6. RTO / Full / Not Controlled

There is an "on ramp" period where autobrake pressure is applied over a period of time. Approximately 750psi is applied in 1.75 sec, then the pressures above are reached in another 1.25sec for autobrakes 1, 2, or 3 and approx. 1.0 sec for autobrake MAX.