Airbus A319 Noise Options

[cshine877]

What is the weird noise they make when they get to the gate and before the push back? It's almost like pump? Or a tightening noise? Anyone know what I mean?

[nianmuzik]

Yes, it is the PTU.

I am no longer 100% sure how it works but if memory serves me right, this is how it is:

During start-up of the second engine (Engine 1 when it is a normal automatic start), the PTU makes a self-test that lasts about 10 seconds IIRC.

After engine shutdown the PTU is de-energized which makes the "barking" noise slow down because both green and yellow systems slowly depressurize.

When you activate the Yellow Electric Pump from the overhead panel (or when a cargo door is opened from down under), the sound of the pump is actually a loud and high-pitched noise.

You cannot hear both noises from the cockpit, but you'll most likely hear them in the cabin, especially if your sitting near the overwing emergency exits.

When dead-heading in the passenger cabin, we would sometimes tell curious passengers (as a joke of course) that there was carpenter in the cargo compartment opening the cargo doors with a saw.

Hope this helps.