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I'm just curious as to what the noises are that you can hear as a passenger in the cabin of an airliner?

For example (ignore the crew talking), the noise at 7:09 - 7:30 on this video; is that the flaps?

What other sounds might a passenger be able to spot?

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    $\begingroup$ +1 I'm especially interested in barking below the passenger cabin of A319 when leaving/arriving a gate. $\endgroup$
    – yo'
    Mar 25, 2014 at 18:34
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    $\begingroup$ ...and on the same type, why is there somebody in the hold sawing through the main spar? Or at least, that what it sounds like. Or is that my interpretation of the same barking noise? I did ask an FO once as he walked down the cabin and muttered something about hydraulics like he had a vague idea but didn't really know. $\endgroup$
    – Simon
    Mar 25, 2014 at 20:03
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    $\begingroup$ @tohecz: The "barking" is the "barking dog pump", or power transfer unit. It pressurizes the two main hydraulic systems (green and yellow) from each other. It briefly runs when the first engine is started. $\endgroup$
    – Jan Hudec
    Mar 25, 2014 at 20:21
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    $\begingroup$ @Jan. I've heard the guy sawing furiously after engine shut down. Also sometimes during gate delays before start. Ah ha, I've just read the link for the PTU. It states A320 but I'm sure that it's on the A319 also. I guess it's the same basic design. $\endgroup$
    – Simon
    Mar 25, 2014 at 20:22
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    $\begingroup$ youtube.com/watch?v=hOZF5y9czS4 At 1:52 you can clearly hear the barking dog on this A319. $\endgroup$
    – user2126
    Apr 15, 2014 at 17:53

4 Answers 4

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There are loads of noises you might hear; there are fuel pumps, hydraulic pumps, air circulation, adjustment screws, servos, and on Airbus aircraft a strange clanking noise when you go over bumps in the tarmac.

On the ground you may hear (and feel) cargo pallets rolling on the hold, and the hold doors being opened and shut. In-flight you have engine noises and air flow noises.

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At that point it was indeed the flaps extending in preparation of takeoff (you can see them moving through the rain).

You would typically also be able to hear the cargo doors closing (before the plane starts taxiing) and the engines ramping up as you start to take off (at 8:54 in the same video).

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  • $\begingroup$ I don't suppose you can find a YouTube clip where you can hear the cargo doors closing? Thanks for your answer btw! $\endgroup$
    – Danny Beckett
    Mar 25, 2014 at 14:08
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    $\begingroup$ you also can hear the gear extension/retraction $\endgroup$
    – Federico
    Mar 25, 2014 at 14:24
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    $\begingroup$ You can also hear whine (or barking) of electric hydraulic pumps in some airplanes. $\endgroup$
    – casey
    Mar 25, 2014 at 16:08
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    $\begingroup$ @casey: The "barking", at least on Airbus, is the PTU, which is hydraulically powered hydraulic pump. $\endgroup$
    – Jan Hudec
    Mar 25, 2014 at 20:22
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An interesting noise you can hear is the sound of the PTU (Power Transfer Unit) during the A320 startup. It sounds like a cross between a dog barking and someone dragging a wet finger across glass.

https://www.youtube.com/watch?v=9aGsXmNjPRw

What happens is that the PTU is transfering pressure from one hydraulics system to the other to equalize them. Since the pressure is not always unequal between the hydraulics systems, this is not audible during every startup.

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A major noise (and vibration) during the flight is the retraction and extension of the landing gear as well as the wheel brake on the wheels once the gear is fully retracted. The vibration is more noticeable (obviously) on aircraft with the main gear in the fuselage and if you are seated over the main gear.

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