HYD PUMP ELEC 2 (A) and ELEC 1 (B) - when to turn on ???

[Bulva]

HYD PUMP ELEC 2 (A) and ELEC 1 (B) - when to turn on ???

I watched some on  YT videos of B733 booting from Cold & Dark state and saw various times when people turn on HYD PUMP ELEC 2 (A) and ELEC 1 (B).
Some do it after plugging in the GPU, others after starting the APU, and still others after starting the main engines.
What is the correct procedure?
 

[Litjan]

The ELEC pumps usually stay on "all day" - you turn them on in the morning (before the first flight) and then shut them down in the evening (when leaving the aircraft).

You need to have clearance from ground personell to turn them on, often the guy doing the outside check will knock on the plane skin and then give you a thumbs-up when all flight surfaces are clear (because they can move when turning on the ELEC HYD). You do need AC power to turn them, so you will need GPU or APU supplying the main AC buses.

They are turned on very early in the preparation, because running them has the advantage of supplying power to the brakes (in case the accumulator wears down during extended ground time) and also being able to spot leakage during the outside check.

You will normally not turn them off during "the day" - the only reasone I can think of right now is the supplementary procedure "Push back with no bypass pin installed" - where you need to depressurize the A system during pushback.

Cheers, Jan

 

[Bulva]

Thank You very much. This great plane is all the more perfect thanks to Your support and assistance. ;-)