Flight Priority Categories (from MATS Part 1)
4.45 Controllers shall give priority to aircraft according to flight priority
category listed below, where category A is the highest priority and Z is
the lowest priority.
Category Type of Flight
A: Aircraft in emergency (e.g. engine fault, fuel shortage, seriously ill passenger). Aircraft which have declared a ‘Police Emergency’. Ambulance/Medical aircraft when the safety of life is involved.
B: Flights operating for search and rescue or other humanitarian
reasons. Post accident flight checks. Other flights, including
Open Skies Flights, authorised by the CAA. Police flights under
normal operational priority.
C: Royal Flights Flights carrying visiting which have been notified by
Heads of State } NOTAM/Temporary Supplement
D: Flights notified by the CAA carrying Heads of Government or very senior government ministers.
E: Flight check aircraft engaged on, or in transit to, time or weather
critical calibration flights. Other flights authorised by the CAA.
NORMAL FLIGHTS:
i) Flights which have filed a flight plan in the normal way and conforming with normal routing procedures.
ii) Initial instrument flight tests conducted by the CAA Flight Examining Unit.
Z: Training, non-standard and other flights.
From the UK AIP (ENR 1.1.4)
4.1 Non-Standard Flights (NSFs) in Controlled Airspace
4.1.1 A Non-Standard Flight (NSF) in Controlled Airspace is an aerial task that may not necessarily follow published routes or notified procedures; a formation flight of civil aircraft other than for VFR transit of CTA/CTR/TMA; or flights to and from a temporary landing site for multiple short term operations.
4.1.1.1 Applications for NSFs within Controlled Airspace should primarily be made via the NATS Non-Standard Flight Application website (
Non-Standard Flight Applications | NATS) with the minimum 21 or 28 days notice (see paragraphs 4.1.2 and 4.1.6). If applicants are unable to utilise this website, applications may be submitted to the units listed below.
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4.1.2.1 Those applications which are agreed will be allocated a non-standard flight reference number. This is only an approval in
principle and prior clearance must be obtained from the appropriate ATC Watch Supervisor on the day.....
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4.1.2.1.4 Operators are to note that in no circumstances can any discussion be entered into on any frequency in the event that permission
is refused or withdrawn