Aircraft taking off from some airports are required to follow specific flight paths called Noise Preferential Routes (NPRs), unless directed otherwise by air traffic control.
The NPRs at Heathrow, Gatwick and Stansted are designated and overseen by the Secretary of State for Transport (not the CAA), and were designed to avoid the overflight of built-up areas where possible. They set a path for the aircraft to take from the runway until they reach the main UK air traffic routes.
An aircraft’s ability to follow an exact route is affected by factors such as:
- navigational equipment,
- the type and weight of aircraft,
- weather conditions – particularly winds that may cause drifting when aircraft are turning
Each NPR is contained in a corridor extending 1.5 km either side of the NPR centre line. Aircraft flying inside this corridor are considered to be flying on-track.
Once an aircraft reaches the NPR release altitude (typically 4,000 feet), a controller can instruct it to turn onto a more direct heading to its destination, which may take the aircraft outside the NPR corridor - this is called vectoring. There may be occasions where it is necessary for safety reasons (e.g. to avoid severe weather conditions) to vector aircraft off NPRs below the release altitude.
Any change to the dimensions of NPRs would require the approval of the Secretary of State for Transport.
Complaints or comments about NPRs should be addressed to the Secretary of State for Transport for issues at Heathrow, Gatwick or Stansted and to the airport itself for other locations.