767 BRAKE ACCUMULATOR

[jpilotj]

Hey Guys,

How many brake applications would you expect to get from an accumulator on a 767 if you had lost all hydraulic pressure?

Many thanks

[DunePrune]

767 accumulator is not for stopping the aircraft, only for applying the parking brake when the hydraulic systems are unpressurised. If you were moving and lost all hydraulics you would have a limited number of accumulator applications, the number depending on how hard you pushed the brakes each time.

[LongLats]

1. Simple as that.

[EMIT]

Accuracy

Hey mates,

Please be accurate in your questions and answers.

767 accumulator is not for stopping the aircraft

if you had lost all hydraulic pressure?

The brake accumulator is the last kettle than contains hydraulic pressure to actuate the brakes, so, in certain circumstances it will be the last source usable for stopping the aircraft (that principle goes for any type of airliner).

Brake systems are usually powered via 2 hydraulic systems (normal and alternate), out of the 3 hydraulic systems that are often available in airliners.

So, on the 767, CTR and R HYD SYS FAIL would leave you with accumulator pressure only for the brakes, while safely landing the aircraft would be done on L hydraulic pressure.

Accumulator pressure should be enough to bring the aircraft to a stop out of a landing. Every application of brakes taps pressure from the accumulator, so don't pump the brake pedals and don't brake so hard that anti-skid releases brake pressure for you. Try to make one steady brake application.
After stopping on the runway, do not taxi further, counting (on) the number of applications that some expert on PPRUNE once gave you.

[Piper19]

Seven full applications is what we mechanics are told. It's also the average needed when we want to remove the pressure from the accu through the pedals for servicing. (If you're a 767 pilot, press reserve brakes till the accu is fully charged, release the switch and all hydr systems off. Now count the amount of pedal pushes till you hit the red band on the brake press gauge, which is the residual air pressure). Place chocks first

Also, on the answer above, antiskid normally doesn't function in this emergency I think (can be I mess up with Airbus now though...)

[flyingchanges]

IIRC, you will have normal anti skid on the accumulator on both the 757 and 767 as it is using the same system as normal brakes.