 On 27 February 1987 , Chinook HC Mk1 ZA721 crashed in the Falkland Islands on a test flight following servicing . After leaving RAF Mount Pleasant , the helicopter was at a normal cruising speed and an altitude of between 300 and 700 feet when it nosed down and crashed into the ground about 6 kilometres south @-@ east of the airfield ; it was destroyed by a subsequent fire . The board of enquiry was unable to determine the exact cause but it may have been the forward @-@ swivelling upper boost actuator jamming . All seven on board , three crew and four technicians , were killed . 
