On Airbus aircraft, before taxiing and before take off, pilots turn auto brakes to MAX.

But on Boeing aircraft, they will set auto brakes to RTO.

Why does Boeing not use auto brakes MAX instead of RTO?

  • $\begingroup$ Welcome to Av.SE! $\endgroup$ – Ralph J Apr 1 '19 at 1:41
  • $\begingroup$ THank you @ Ralph J $\endgroup$ – user9935 Apr 1 '19 at 20:36
  • $\begingroup$ What does RTO stand for? $\endgroup$ – Robin Bennett Aug 12 '19 at 8:38
  • $\begingroup$ @RobinBennett RTO stands for Rejected Takeoff. $\endgroup$ – J.Torre Aug 17 '19 at 14:21

For the 737:

RTO is used for takeoff, and puts full hydraulic system pressure to the brakes. The other autobrake settings, 1, 2, 3, and Max, are used for landing, and brake to achieve a specified deceleration rates. In autobrakes Max, you get very firm brake application, but it's still something less than unmetered system pressure to the brakes.

In all cases, the anti-skid system will prevent a wheel from locking up by reducing (modulating, actually) hydraulic pressure to a particular brake.

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    $\begingroup$ You may want to add that this is for Boeing aircraft. Airbus simply uses different terminology: MAX is equivalent to Boeing's RTO and never used for landing. $\endgroup$ – Bianfable Apr 1 '19 at 8:00
  • $\begingroup$ @Bianfable Good call - edited. Thanks! $\endgroup$ – Ralph J Apr 1 '19 at 14:47
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    $\begingroup$ If I understand correctly: 1, 2, 3 & Max are for landing and will slow the plane with increasing urgency (runway length & request/desire to vacate the runway ASAP), while maintaining control and preserving brakes & brake temps. RTO is damn the torpedoes, we need to stop this thing before we run out of pavement even if it leads to brake fires and/or exploding tires. $\endgroup$ – FreeMan Apr 1 '19 at 17:59
  • $\begingroup$ Thanks for the comments, I conclude Airbus MAX is equal to Boeing RTO. $\endgroup$ – user9935 Apr 1 '19 at 20:33
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    $\begingroup$ @Vijay While I'm not familiar with the Airbus, that's exactly what it sounds like in light of Bianfable's comment above. Boeing calls the takeoff setting "RTO" while Airbus calls it "Max". $\endgroup$ – Ralph J Apr 2 '19 at 4:54

On a Boeing 737,

1, 2, 3, and MAX deceleration positions command the autobrake system during landing brake control to modulate brake pressure until the airplane is at a full stop.

The rejected takeoff (RTO) position commands the autobrake system to apply full pressure to the wheel brakes and stop the airplane. The autobrake system operates in RTO when the pilot starts a rejected takeoff at groundspeed more than 88 knots.

The 1, 2, 3 and MAX deceleration positions have different control logic from the RTO position.

RTO Application Logic:

The autobrake function applies the brakes when these conditions occur:

• RTO autobrake is armed

• Two thrust levers are in the idle position

• All wheel speeds average more than 88 knots

• No fault in the normal antiskid system

• Two normal metered pressures are less than 750 psi.

When the RTO autobrake function applies the brakes, it energizes a relay in the antiskid/autobrake control unit. This sends power to the solenoid and control valves on the autobrake pressure control module.

The autobrake system sends full hydraulic pressure to the brakes to slow and stop the airplane.

Landing Application Logic:

The autobrake function applies the brakes when these conditions occur:

• Landing autobrake is armed

• Both thrust levers at idle

• Either air/ground system continuously indicates ground for 0.2 seconds (if wheel spin-up occurs more than one second before ground is sensed) or 0.7 seconds (if wheel spin-up is occurs less than one second before ground is sensed).

• Wheel spin-up detection occurs or the spin-up latch sets.

Wheel spin-up detection occurs when one wheel on each main landing gear increases to 60 kts or greater and the wheel speed stays above 30 kts. (Source: 737NG AMM)

Therefore, after accelerating to an average wheel speed above 88 knots during takeoff, the RTO autobrake will be applied if the thrust is retarded to idle. When the airplane touches the ground and the thrust levers are put to idle, the 1, 2, 3 or MAX autobrake will be engaged.

On an Airbus 320, however, maximum mode is normally selected for take-off and medium or low modes are selected for landing.

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