Former President George HW Bush has celebrated his 90th birthday by jumping out of a helicopter from 6,000 feet.Mr Bush, who no longer has use of his legs, made the tandem parachute jump near his summer home in coastal Maine.In doing so, the ex-president followed through on a vow he made five years ago.A retired member of the US Army's parachute team, the Golden Knights, helped guide the former commander-in-chief to the ground.