By Nathan Raab

What's That Noise? Common Sounds on an Aircraft Explained

Understanding the Sounds of Flying

Air travel can be a noisy experience — and for some passengers, unfamiliar sounds can spark anxiety or curiosity especially if you haven't got a window seat which heightens your hearing. From random beeps to strange vibrations, the cabin can feel like a soundscape from another planet. But here’s the truth: almost every sound you hear is completely normal and part of a well-oiled safety and communication system.

In this blog, we’ll break down the most common noises heard on board, and what they actually mean. So the next time you fly, you can sip your Jumbo Jet Espresso in peace, knowing exactly what’s going on.


Cabin Chimes and Dings

Intercom Calls

These are among the most frequent sounds you’ll hear onboard. Cabin crew use the interphone system to call each other or the flight deck. A single chime usually means a routine call made on the interphone between crew or a passenger pressing their call bell; a double or triple chime is just another way to communicate something. For example a double chime might be used to tell the crew we are about to line up on the runway and take off.

Passenger Call Bell

Every seat has a call bell button. When pressed, it pings a soft ding to alert the cabin crew and you'll then see a light above the passenger seat illuminate.

Seatbelt Sign

When the seatbelt sign is switched on or off, you’ll hear a loud ding across the cabin. A double-ding (on-off-on quickly) for some airlines means takeoff — a discreet way for the pilots to signal cabin crew.

The Barking Dog Sound: The PTU

One of the most confusing and comically nicknamed sounds is the "barking dog" noise often heard once the aircraft has pushed back off stand or is taxiing onto stand. This is the Power Transfer Unit (PTU), which transfers hydraulic pressure between systems if only one engine is running on the ground. It’s loud, rhythmic, and completely normal. It runs a self-test during ground operations or engine start-up depending on aircraft type. Another high-pitched tone you might hear after boarding is from the aircraft’s hydraulic system. This usually happens when the ground crew closes the baggage doors — a process that uses hydraulic power and can trigger that brief, whining noise. It’s totally normal and nothing to worry about.


The Whirr of Flaps and Slats

As you approach takeoff or landing, you’ll hear motors whirring from the wings. These are the flaps and slats extending or retracting. They increase lift at slower speeds and are a routine part of configuring the aircraft for different phases of flight.

You may also feel or hear:

Vibration or humming near the wings

A steady mechanical movement sound

Again, totally normal — just physics and engineering in action.


Speedbrakes and Spoilers

You might hear an air buffeting noise or feel a subtle deceleration/light bumps during descent. That’s the speedbrakes or spoilers deploying on top of the wing to reduce speed and increase drag. It might feel like a drop in power or a loud whoosh, but it’s completely normal and you will see them being used if you have a window seat. 

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Engine Noise Changes After Takeoff

Immediately after takeoff, you might hear the engines spool down slightly. This is often due to thrust reduction as the aircraft transitions from takeoff to climb thrust. It saves fuel and reduces wear on the engines. This is often described by passengers as, 'feeling like the plane is dropping' but, this is your senses tricking you and we are still climbing away from the ground at a rate of thousands of feet per minute. After that, we retract the flaps on our wing which will also create a motor noise and feel like a slight drop in your seat.

During very cold winter weather on the ground, it’s completely normal for us to briefly increase engine power to around 50% thrust at regular intervals. This is called an ice shedding procedure, and it helps prevent ice from forming on the engine fan blades. To passengers, it might sound like the aircraft is about to take off and then suddenly stops — but rest assured, it’s a routine safety measure that often goes unnoticed.

What Lightning Really Sounds Like

Believe it or not, aircraft are designed to withstand lightning strikes. When it happens, it may sound like a loud crack or thump, often accompanied by a bright flash. Modern aircraft are built with conductive materials and lightning diverters that safely channel electricity away from critical systems.

The aircraft is inspected after landing, but most strikes leave no damage at all. Again, a noise that is very rare but completely normal. On average an aircraft is struck by lighting every 3000 flight hours. This is an average, in Europe it is a lot rarer to be stuck by lighting than flying around the tropics for example.


Final Thoughts

Flying comes with a symphony of sounds — but once you understand what each one means, the noise becomes comforting, even reassuring. From barking dogs to secret seatbelt chimes, every sound has a purpose.

Nathan Raab
Airline Pilot | Better Coffee Advocate | Jet Bean Founder

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