Which plane noises should I be worried about?

Which plane noises should I be worried about?

Nervous fliers have a tendency to scrutinise every little bump, whirr and thud they hear on board a plane. Was that a wheel falling off? Did the wing just crack? I could swear I just heard the pilot snoring in the cockpit…

But which sounds are routine and which should have you reaching for the in-flight safety card?

The issue of aircraft noises has been and the responses – including two from aviation experts – might just help you relax next time you’re in the sky.

Firstly, remember than aeroplanes are generally noisy, creaky beasts, particularly in turbulent conditions.

“The logical assumption is that everything on an aeroplane – the bins, seating sections, loos and galleys – is bolted down,” explains Marc Levy, a mechanical engineer who says he has worked for Boeing. In reality, overhead bins “hang from a sets of tie rods”, lavatories and galleys “are mounted to tracks in the floor”, and so on, meaning “when you give the aeroplane a little jolt, all the stuff on the inside is going to adjust and sometimes bump into things”.

Mike Leary, another former Boeing employee, goes further, providing a checklist of all the normal noises you may or may not hear during your next flight.

The humming noise when you board

That’s the auxiliary power unit at the back of the plane. “That baby hums along while you are boarding the plane to keep every thing up and running while the main engines are off,” says Leary. “In addition, most airports hook the plane up to the ground units to pump air and electricity into the plane to save money.” When the doors close, you may notice the noise changes, and the lights will flicker, as the pilot switches from the airport system to the aircraft system. Next you’ll hear the engine’s being started – first “the whine of the spin-up” and then “the roar”.

What’s that barking sound?

It’s probably not a dog in the hold (although there’s a very small chance it might be – , but a fuel saving device called the PTU, present on all twin-engine Airbus models. “It is making sure the hydraulic pressure is balanced when they only use one engine during push-back and taxiing,” says Leary. “Everyone wants to save fuel so this is their option. It’s noisy and a bit unnerving as it cycles on and off, on and off, on and off due to pressure fluctuations. It sounds like a high pitched bark to some: woof-woof-woof-woof…”

Airbus passengers may also hear a “prolonged whine” by the gate prior to departure and then after landing. “It’s from an electric hydraulic pump used to open and close the cargo doors,” says Leary.

What’s that barking sound? It’s probably not a dog in the hold (although there’s a very small chance it might be – more on that here), but a fuel saving device called the PTU, present on all twin-engine Airbus models. “It is making sure the hydraulic pressure is balanced when they only use one engine during push-back and taxiing,” says Leary. “Everyone wants to save fuel so this is their option. It’s noisy and a bit unnerving as it cycles on and off, on and off, on and off due to pressure fluctuations. It sounds like a high pitched bark to some: woof-woof-woof-woof…”

Airbus passengers may also hear a “prolonged whine” by the gate prior to departure and then after landing. “It’s from an electric hydraulic pump used to open and close the cargo doors,” says Leary.

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