For a nervous flier, an errant creak or beep on board might make you sweat (or reach for the Xanax). Thankfully, the myriad sounds are completely normal—and you should expect to hear them whenever you fly. “Aircraft make some very standard sounds when certain pieces of equipment are moved," Ron Carr, a former pilot and assistant professor of aeronautical science at Embry-Riddle Aeronautical University tells Condé Nast Traveler. "Airplanes move parts in order to increase aerodynamic forces or decrease aerodynamic forces, the same way a car makes certain noises as it is driven.”
Here are five common sounds you might hear when flying and what they mean:
A "Poof" of Air at the Gate
One of the first noticeable sounds you’ll hear before you takeoff is a loud poof as the ventilation switches from an outside system to one inside the aircraft. The lights will also flicker as they transition to the plane system, known as the APU, or axillary power unit. It saves money to connect to outside systems when airplanes are on the ground.
A "Bark" as the Plane Taxis
When the plane taxis, whether before departure or after arrival, the plane will make a weird barking sound. That’s the hydraulics, or the system that helps steering, braking, and air pressure, among other functions on board. There’s a device called a power transfer unit, or PTU, that balances the hydraulics and makes that lovely noise.
"Whir" of the Wings
Before your plane takes off and after it’s in the air, you’ll hear a whirring sound as the flaps first increase the wingspan and then retract to help give lift, so the plane can take off and maintain air speed. Again, totally normal.
"Bang" From the Belly
As the plane begins its final descent, generally around 2,000 feet, a flap under the wing opens and the landing gear drops. This is often accompanied by a bang, which can be loud, but is perfectly fine. The wheels stay tucked during the flight so they don’t create drag, which would interfere with the plane’s aerodynamics.
"Screech" of the Brakes
When the plane lands, you’ll hear the loud screech of the brakes. It doesn’t mean your pilot is a crazy driver or that the brakes need a tune-up. Rather, the plane just needs to maintain a certain speed to reach the runway, generally around 100 to 150 miles per hour, and that it has the length of the runway to stop a 400,000-pound plane filled with people and luggage.