Short answer: Almost every sound on an airliner is a system doing its job. At the gate you hear bags being loaded, the small engine in the tail and the air conditioning. On takeoff the engines roar, then the landing gear thunks away. On descent the flaps whir and the gear rumbles down. After touchdown the engines roar again to help slow you down.
Key facts
- The auxiliary power unit (APU), a small engine usually in the tail cone, powers the airplane's systems and air conditioning at the gate and supplies air to start the engines [1].
- Noise-abatement rules let pilots reduce from takeoff thrust once they're at or above 800 feet, so the engines often get quieter early in the climb [2].
- US airline rules treat taxi, takeoff, landing and other flying below 10,000 feet (except cruise) as "critical phases of flight" [3].
- Cabins are typically pressurized to the equivalent of 6,000 to 8,000 feet, and US rules cap normal cabin altitude at 8,000 feet [4][5].
- On many Airbus jets, a "barking dog" sound during taxi comes from the power transfer unit (PTU), which keeps hydraulic pressure up when one engine is off [6].
- Ear pressure is usually most noticeable on descent, because air pressure rises as the plane gets lower [7].
Why airplanes are noisy (and why that's good)
An airliner is full of motors, pumps, fans and moving surfaces, and the cabin is a thin metal tube that carries their sounds to you. Most noises happen at the same moments on every flight because they're steps in a checklist: start the engines, set the flaps, raise the gear, lower the gear.
Once you know the order, the noises become a kind of progress bar. A thunk after takeoff isn't something going wrong; it's the next box being ticked.
Every normal sound, phase by phase
| Phase | What you hear | What it is |
|---|---|---|
| At the gate | Thumps and bangs under the floor | Bags and cargo being loaded into the hold |
| At the gate | A steady hum or whine, even before the engines start | The APU in the tail, powering lights and air conditioning [1] |
| At the gate | A rush of air from the vents | Air conditioning, often supplied by the APU [1] |
| Engine start | A rising whine, then a deep hum | Each engine spinning up, usually started with air from the APU [1] |
| Taxi | Rumbles and bumps | Wheels rolling over joints in the taxiway |
| Taxi | A whir from the wings | Flaps and slats extending for takeoff |
| Taxi (Airbus) | A short, repeated "barking" or grinding | The power transfer unit balancing hydraulic pressure [6] |
| Takeoff roll | A big roar and a push into your seat | The engines at takeoff power |
| Just after liftoff | A thunk or two below you, then quieter wind noise | The landing gear folding up and the doors closing |
| Early climb | The engines suddenly get quieter | Thrust reduced from takeoff to climb power [2] |
| Climb | A whir from the wings | Flaps and slats retracting as speed builds |
| Climb and cruise | Ding chimes | The crew's call system and seat belt sign |
| Cruise | A steady hum and air noise | Engines at cruise power; air flowing over the fuselage |
| Descent | The engines go quiet; sometimes a rumble or vibration | Engines near idle; speedbrakes on the wings to control speed [8] |
| Approach | Whirs from the wings | Flaps and slats extending for landing |
| Approach | A rumble, a thud, and more wind noise | The landing gear coming down and locking |
| Touchdown | A thud, then a loud roar | Wheels meeting the runway, then reverse thrust [9] |
| After landing | Panels rising on the wings | Ground spoilers dumping lift so the brakes work better [8] |
At the gate and during taxi
Thumps under the floor. The hold is right under your feet, and bags are being loaded. Cargo doors close with a clunk.
The hum before the engines start. That's usually the auxiliary power unit, a small engine normally located in the tail cone [1]. It runs the electrics and the air conditioning so the airplane can operate without ground equipment, and its air is used to start the main engines [1].
The barking dog. On many Airbus jets, flyers hear a short, repeating bark or grinding sound during taxi. It's the power transfer unit (PTU), a device designed to keep hydraulic pressure up during single-engine operations [6]. Airlines often taxi on one engine to save fuel; the PTU then lets the running engine's hydraulic system help the other one, and it switches on and off as pressure changes [6]. It's normal, not a malfunction [6].
Bumps on the taxiway. For many flights, the taxi is the bumpiest part of the day. The wheels roll over joints in the concrete, and every one comes up through the seat.
Takeoff and climb
The roar. The engines go to takeoff power and you're pressed back into your seat. The sound builds through the roll until the wings lift you up.
The thunk below you. A few seconds after liftoff, the landing gear folds into the belly and the gear doors close. It can sound surprisingly mechanical. It's one of the best sounds of the flight: the airplane is climbing as planned.
The engines get quieter. This surprises many nervous flyers. After takeoff, pilots reduce from takeoff thrust to climb thrust, often as part of noise-abatement procedures that set the reduction at or above 800 feet [2]. The airplane keeps climbing smoothly; it simply doesn't need full power anymore.
Whirs from the wings. As speed builds, the flaps and slats slide back into the wing. You may hear a whine from the motors that move them. That's normal: the wing is changing shape for faster flight.
Ears popping. As the airplane climbs, the cabin is pressurized to the equivalent of about 6,000 to 8,000 feet [4]. US rules cap it at 8,000 feet in normal operation [5]. Your ears adjust as the pressure changes; swallowing helps.
Cruise
Dings. Chimes are how the pilots and cabin crew call each other, and how the seat belt sign announces itself. Each airline uses its own patterns. A chime isn't an alarm.
Pilots also keep a "sterile cockpit" during critical phases. US rules define these as taxi, takeoff, landing and other flying below 10,000 feet, except cruise [3]. Some airlines mark passing that height with a chime, and cabin service often starts soon after.
The hum. A steady engine hum and the rush of air over the fuselage are the background music of cruise. Changes in pitch usually mean small changes in power or altitude. If bumps join in, with a few creaks from the cabin panels, that's turbulence; read is turbulence dangerous? for why the airplane takes it in stride.
Descent and landing
Quiet engines and a gentle tilt. The descent often begins with the engines easing toward idle and the nose tipping down slightly.
A rumble or vibration in descent. Pilots may use speedbrakes, panels on top of the wings that add drag, to control speed during descent [8]. You can feel a light buzz through the floor. It stops when they're stowed.
Whirs, then a rumble and a thud. Flaps and slats extend in stages for landing. Then the landing gear comes down: a rumble of air as the doors open and a firm thud as the gear locks.
Ears again. Descent is when ears notice the change most, because air pressure rises as the airplane gets lower [7]. Swallowing, yawning or chewing helps air reach the middle ear [7].
Touchdown and the roar. A thud as the wheels meet the runway, often followed by a loud roar. That's reverse thrust: engine thrust directed the opposite way, which can significantly increase deceleration [9]. At the same time, ground spoilers rise on the wings to dump lift and put the airplane's weight on the wheels so the brakes work well [8]. A firm landing is often deliberate, for good grip on the runway.
Sounds worth mentioning to the crew
Almost everything you hear is routine, but you never need a reason to ask. If a sound worries you, ask a flight attendant: they hear the same airplane all day and will tell you what it is. For more on what happens when, see what to expect on a flight.
Using sounds to feel calmer
Many nervous flyers find it helps to turn sounds into a checklist: "engines started, flaps set, gear up, power reduced." Each sound becomes proof that the flight is following its plan. Pair it with slow breathing from our guide to calming anxiety on a plane, and see nervous flyer tips for planning the rest of your trip. If noises are only one part of a bigger worry, our guide to fear of flying explains what helps most.
How Sorapuff helps
Sorapuff's flight tracker follows your flight from the schedule and from what your phone feels, so it works in airplane mode. At each phase, Sora explains what you may hear right then: the bags thumping under the floor, the gear folding away, the engines easing back after takeoff, the flaps whirring before landing. The tracker is free (pricing). It's information and comfort, not a flight instrument; always follow your crew.
FAQ
What is the loud thump after takeoff?
It's almost always the landing gear retracting. A few seconds after liftoff, the wheels fold up into the belly of the airplane and the gear doors close, which can sound like a firm thunk or clunk under your feet. It means the takeoff went to plan. The wind noise often drops a little right after.
Why do the engines get quieter after takeoff?
Pilots reduce from takeoff thrust to climb thrust once the airplane is safely airborne, often under noise-abatement procedures that allow the reduction at or above 800 feet. The airplane doesn't need full power to keep climbing, and the reduction is part of the normal plan. It can feel like slowing down, but the airplane is still climbing.
What is the barking sound on an Airbus?
It's the power transfer unit (PTU), part of the hydraulic system. When one engine is shut down during taxi, which airlines often do to save fuel, the PTU lets the running engine's hydraulic system support the other, switching on and off as pressure changes. That on-off cycling makes the bark. It's normal and not a sign of a problem.
What are the dings on a plane?
Dings and chimes are the airplane's call system. Pilots and flight attendants use them to call each other, and a chime also sounds when the seat belt sign switches on or off. Each airline has its own chime patterns. A chime is a message between the crew, not an alarm.
What is the whirring noise before landing?
That's the flaps and slats extending from the wings. They make the wing bigger and more curved so the airplane can fly slowly and safely for landing, and they move in stages, so you may hear several whirs. Shortly after, you'll hear a rumble and a thud as the landing gear comes down and locks.
Why is it so loud after the plane lands?
After touchdown, pilots often use reverse thrust: the engines direct their thrust the opposite way to help slow the airplane, which can significantly increase deceleration. It sounds like a loud roar for a few seconds. Panels also rise on the wings to put the airplane's weight on the wheels so the brakes work well.
Sources
- Auxiliary Power Unit (APU), SKYbrary Aviation Safety
- Civil Aviation Rules Part 93, Appendix D (noise abatement take-off procedures), Civil Aviation Authority of New Zealand
- 14 CFR § 121.542, Flight crewmember duties, Legal Information Institute (Cornell Law School)
- Air Travel, CDC Yellow Book 2026, Centers for Disease Control and Prevention
- 14 CFR § 25.841, Pressurized cabins, Legal Information Institute (Cornell Law School)
- The Barking Dog: Those Strange Noises on Airbus Planes, Ask the Pilot
- Ears and Flying (2024), Patient.info
- Spoilers and Speedbrakes, SKYbrary Aviation Safety
- Reverse Thrust, SKYbrary Aviation Safety