CFS Percival Proctor Mk IV. Royal Air Force United Kingdom. The Percival Proctor was a British trainer and communications aircraft of the Second World War. The Proctor Mk IV was a single-engine, low-wing monoplane with seating for four. Repainted as RAF Proctor Mk IV # RM221, yet today airworthy and based at Biggin Hill. FS98 Aircraft Designers.. Frank Elton & PEGASUS AVIATION DESIGN. RAF BMP textures and DP for CFS. Edmundo Abad Jan. 2011.