Promotional film for the Hawker Siddeley HS-121 Trident 3. Engineers decided to add a fourth engine in the tail, the tiny Rolls-Royce RB162 turbojet, fed from its own intake behind a pair of movable doors. The engine added 15 per cent more thrust for takeoff, while adding only 5 per cent more weight, and it would only be used when needed. BEA accepted this design as the Trident 3B, and ordered 26. The first flight was on 11 December 1969 and the aircraft entered service on 1 April 1971. Addition