Not all aircraft, and not all flight movements, produce the same noise or are perceived as equally disturbing. This is due to several factors: 

Engine noise as a major source during take off

Aircraft engines are among the main noise sources during departure. Several types of noise are generated, for example:

• Fan noise: The sound of air being drawn through the engine fan. This noise is especially noticeable during taxiing and take off.
• Core noise: Noise produced by the mechanical and thermodynamic processes in the engine’s compressor and combustion chamber. It becomes more pronounced at high engine power. 
• Jet noise: Noise created by the extremely fast exhaust jet leaving the engine. This is particularly loud during take off and the initial climb.

Noise from the aircraft body

The aircraft’s airframe also generates noise, for example through:

• Flaps and slats (high lift devices)
• Landing gear
• Airflow turbulence around the fuselage (airframe noise)

Tonal characteristics

Tonal noise can make an aircraft seem louder or more noticeable. Some aircraft generate tones at specific frequencies that stand out, for example, a high pitched whine that is perceived as particularly prominent or unpleasant.

Aircraft noise is usually loudest during take off. How loud an aircraft is heard on the ground depends on several factors, including:

• Size and type of aircraft
  Larger or older aircraft often generate more noise than smaller or more modern types.
• How the aircraft is flown
  ​For example, the engine thrust used for take off can influence how loud the aircraft is.
• Rate of climb
  ​Heavy long haul aircraft often climb more slowly and therefore remain audible for a longer time.
• Weather conditions
  ​Wind direction, temperature and humidity all influence how sound propagates.
• Altitude of the aircraft
  ​Altitude plays a major role: an aircraft flying at low altitude is significantly louder than the same aircraft at higher altitude.

In addition to aircraft noise, there are many other noise sources at the airport that are not directly related to take off or landing but are essential for airport operations and ground handling. These include, among others:

• Taxiing of aircraft: movements between the gate and the runway.
• Ground handling activities involving various vehicles and equipment, such as:
  - catering vehicles
  - baggage carts and tugs
  - Ground Power Units (GPUs) providing electrical power to parked aircraft
• Buses transporting passengers between the terminal and the aircraft
• APU (Auxiliary Power Unit): small auxiliary engines located in the tail section that provide electrical power and air conditioning while the main engines are shut down
• On site service and maintenance traffic on the apron and taxiways, e.g. maintenance vehicles or refuelling trucks
• Engine run ups, in some cases performed in special noise reduction facilities
• Car parks and access roads: traffic within the airport area also contributes to the overall sound environment
• Construction sites: construction noise is classified neither as industrial and commercial noise nor as aircraft noise
• Bioacoustic signals: during bird scaring operations, airport wildlife control may use scare guns