EI-ROG

I'm curious about some noises on the BAe 146/RJ, which I hope some '146 drivers or techies can answer for me - and no, it's not the usual flaps question....

Prior to pushback, a short, sharp, hydrualic-sounding whine can often be heard for about 3 or 4 seconds. It doesn't always happen, and seems to me to occur mostly on the '146 rather than the RJ. Occasionally, I've also heard it run continuously from takeoff, until a few minutes after flap retraction. In the latter case, it's activated again on approach, prior to flap extension, through to the taxy.

My best guess is that the noise comes from either the AC pump, DC pump, or the brake accumulator. I'd be grateful if anyone could identify it for me.

It can be heard in the linked video. The sound starts following touch-down at 5:59.

YouTube - LFSB-EHAM

Thanks in advance.

Longhitter

It's the AC pump. On aircraft without an auto mode on it the AC pump must be on for take-off and approach / landing. The 3-4 seconds on the ground is most likely to top up brake pressure.

EI-ROG

Thanks very much, Longhitter. That clears that up.