PPRuNe Forums - Changing auto brake setting during roll out

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- - Changing auto brake setting during roll out (https://www.pprune.org/tech-log/614604-changing-auto-brake-setting-during-roll-out.html)

Quote:

Originally Posted by Uplinker (Post 10855456)

Actually sorry, no I was briefed on it very comprehensively but never actually flew it - my bad :ugh:

I'll get my coat.........

No worries. It’s dirt simple and heaps of fun. Keep the road to your left, then follow the lights in. Have an eye on the PAPI (which is offset so you can see it in the turn).

Quote:

Originally Posted by Fursty Ferret (Post 10855138)

If you're not capable of smoothly disconnecting the autobrake and modulating the brakes to an appropriate level manually then IMHO you shouldn't be flying a passenger aircraft. Or driving a car, frankly...

To deride fellow professionals based on the assumption that they cannot do something because they choose one way of doing that something as and when it's suitable is laughable.

I did it once or twice on the Airbus and found it mildly satisfying but I would advise against routinely using it as your go-to auto brake deselection method.

Quote:

Originally Posted by Kirks gusset (Post 10849797)

The Autobrake settings equate to pressures:
• Autobrake setting 1 - 1250 PSI equates to 4 ft per second squared.
• Autobrake setting 2 - 1500 PSI equates to 5 ft per second squared.
• Autobrake setting 3 - 2000 PSI equates to 7.2 ft per second squared.
• Autobrake setting MAX and RTO - 3000 PSI equates to 14 ft per second (above 80 knots) and 12 ft per second squared (below 80 knots).

If the autobrake is stopping you too quickly, then it's easy to as the PM to select a lower setting, or simply gently apply brakes until the disarm like comes on, at this point you will have the same pressure as the system, conversely if more stopping is required either select a higher setting or apply brakes gently and increase the pressure. The common mistakes are jolts from over ambitious disarming via the switch or stamping on the brakes.
Remember some landing conditions dictate the use of autobrakes so its not a personal choice
Its much safer usually to manually brake to make the required adjustments rather than have heads down in the cockpit,

Forgive me, but how can a brake pressure in PSI possibly equate to a specific deceleration rate? Wind, weight, touchdown speed... They're all going to affect that MASSIVELY. Surely the autobrake setting modulates brake pressure to give the desired deceleration rate upto the max brake pressure? I'm not saying it doesn't apply that specific pressure in PSI but there is no way that a pressure can remotely guarantee a deceleration rate - even on the worlds most perfect and dry runway.