Air Traffic Control Instruction

An air traffic control instruction is a directive issued by an ATC unit requiring a pilot to take a specific action. Unlike a clearance, which authorizes a course of action, an instruction directs one. Pilots are required to comply with ATC instructions unless doing so would compromise the safety of the flight.

Compliance and Deviation

A pilot who cannot comply with an ATC instruction must advise ATC immediately using the phrase “UNABLE” and state the reason. If safety requires immediate deviation, the pilot must manoeuvre as necessary and advise ATC as soon as possible. The PIC always has final authority over the safe operation of the aircraft.

Related Terms

See also: ATC Clearance, Readback, Pilot-in-Command.