Master aircrew (MAcr) is the warrant-officer rank held by aircrew in the Royal Air Force. It is equivalent to warrant officer in other trades, and is effectively the highest non-commissioned aircrew rank. It has a NATO rank code of OR-9.
People holding this rank are actually referred to by different titles depending on their specialisation: master signaller (MSig), master engineer (MEng), master air electronics operator (MAEOp) and master air loadmaster (MALM). This rank is the sole survivor of a system of separate ranks for aircrew which existed between 1 July 1946 and 1950 (another system for technical staff existed between 1950 and 1964). Other designations, such as master pilot and master navigator, once existed, but now these specialisations are only held by officers.
The badge of rank is a small version of the Royal Arms (as worn by a warrant officer) with an eagle below, all surrounded by a wreath. Master aircrew receive a warrant signed by the Secretary of State for Defence.