AIRCRAFT NOISES AFTER TAKE OFF - The retraction of the undercarriage is the most significant noise just after take off. Passengers will hear firstly the deployment of the main undercarriage doors and then the undercarriage itself retracting followed by the closing of the doors. This is typically followed by a reduction in the aerodynamic wind noise associated with having the undercarriage deployed. Shorty after the undercarriage is retracted and once the aircraft reaches certain airspeeds the trailing edge flaps and leading edge slats will be gradually retracted.

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Aircraft Noises After Take Off

WHAT ARE ALL THOSE NOISES AFTER TAKE OFF?

By Airline Ratings

Variety of noises

Just after takeoff the most significant noise is the retraction of the undercarriage.

Passengers will hear firstly the deployment of the main undercarriage doors and then the undercarriage itself retracting followed by the closing of the doors.

If you are lucky enough to be sitting in the very front of a 747 you will also hear the spinning nose wheel as it retracts right under where you are sitting.

This is typically followed by a reduction in the aerodynamic wind noise associated with having the undercarriage deployed.

Shorty after the undercarriage is retracted and once the aircraft reaches certain airspeeds the trailing edge flaps and leading edge slats will be gradually retracted.

Again once these are fully retracted the aircraft is ‘clean’ and aerodynamic wind noise decreases further.

Engine cutback

Many airports around the world require what is called noise abatement procedures.

So shortly after takeoff, passengers may both sense and hear a rapid reduction in power which can be concerning.

Don’t worry… it will almost certainly be the pilots easing power back to reduce the impact of noise on local communities.

Air Traffic

And at some very busy airports air traffic control may keep your flight at a low altitude and thus at reduced power until you clear the area.

So almost certainly your aircraft is fine and the pilots are so busy they may not have the opportunity of telling you what is going on.

Landings

Like takeoff, there are lots of noises associated with landings.

Firstly, however you will have reduced thrust – back to idle – as your flight descends. Then the pilot will start a gradual deployment of the flaps and slats to increase lift while reducing speed.

The pilot may also deploy spoilers on the upper surface of the wing to slow the plane and these often cause a noisy buffeting.

Thrust reversers   

Once the aircraft (jet) touches down pilots will almost always deploy the aircraft’s thrust reverser doors which close behind the engines and deflect the thrust forward to help reduce the aircraft’s speed.

This will be associated with an increase in thrust.

In turboprop planes, the pilots may alter the pitch of the blades to reduce speed and this can also be quite noisy.

https://www.airlineratings.com/did-you-know/what-are-all-those-noises-after-take-off/

THRUST REVERSERS - Jet engines on early jet airliners channel their thrust in the opposite direction for high-speed braking action with “thrust reversers” that redirect exhaust gasses forward using clamshell doors. Today’s powerful and efficient turbofan engines use an aft-sliding ring on the back of the fan section to reverse thrust, with internal doors redirecting fan airflow forward. The ultra-high-bypass turbofan engines used on the Airbus A380 have reversers on the inboard nacelles.

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Thrust Reversers

HOW DO THRUST REVERSERS WORK?

By Airline Ratings 

Although reversing propeller pitch was effective for stopping piston-powered airliners, new methods were needed to bring faster and heavier jet airliners to a safe stop on landing.

Wheel brakes reduce speed from 60 knots down to taxi, but more braking action was needed to slow the airplane from its 120-knot touchdown speed.

While military jets use drag-inducing parachutes deployed on landing, these have to be jettisoned, retrieved, and repacked after every use which would be impractical at a commercial airport.

Jet engines on early jet airliners could channel their thrust in the opposite direction for high-speed braking action with “thrust reversers” that redirected exhaust gasses forward using clamshell doors to block engine exhaust.

Today’s powerful and efficient turbofan engines use an aft-sliding ring on the back of the fan section to reverse thrust, with internal doors redirecting fan airflow forward.

The ultra-high-bypass turbofan engines used on the Airbus A380 have reversers on the inboard nacelles only to avoid causing severe adverse yaw on wet or icy runways.

https://www.airlineratings.com/did-you-know/how-do-thrust-reverses-work/