A mental patient who stormed the cockpit of a jumbo jet had been been escorted to his seat by police officers who thought he was nervous of flying.
The British Airways plane bound for Nairobi plunged out of control after Paul Mukonyi seized the controls.
Before he had boarded the flight at Gate 54 of Gatwick Airport's North Terminal, ground staff had called police officers to calm him down.
Chief Inspector Alan Wingrove, who is in charge of police at Gatwick, said: "He had arrived on a connecting flight from Lyon and thought he had been followed from France.
"He was concerned about the possibility of guns or drugs being smuggled on to the plane but once we had assured him of our security arrangements he calmed down.
"He gave the appearance of being a nervous flyer and showed no signs of mental health problems."
Several passengers of the Boeing 747 were injured when it plunged 10,000ft before cabin crew restrained 27-year-old Mukonyi.
Mr Wingrove said the cabin crew and pilot of the flight had accepted the passenger on board just after 10pm on Thursday.
He said: "We outlined the circumstances to the cabin crew director and she went to receive confirmation from the pilot who has ultimate responsibility.
"She returned a few minutes later and we asked for him to be monitored during the flight.
"He had not committted any offences so we could not stop him getting on."
Rock singer Bryan Ferry and the wife of former cricket ace Imran Khan, Jemima, who was travelling with her two children, brother and mother were amongst the nearly 400 passengers on board.
Mukonyi was arrested when the plane touched down at the Kenyan capital.
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