US authorities are investigating after a British Airways jet was forced to descend sharply to avoid hitting another aircraft over Florida, the airline said.
The pilot was being given instructions by air traffic control to continue climbing from 16,500ft to 20,000ft when the aircraft's emergency avoidance system gave the command "descend, descend, descend", A BA spokesman said.
Cabin crew went into freefall, hitting their heads on the ceiling of the Boeing 777 as it plunged 600ft to avoid colliding with another aircraft flying overhead, he said.
Two of the 175 passengers and four crew suffered minor injuries in the dramatic dive just 15 minutes after taking off from Tampa airport.
Those with bumps and bruises were later treated in the Club Class area.
Having taken off from Tampa at 6.30pm on October 10, the flight landed at Gatwick at 8am the following day.
The airline's spokesman said: "We have no idea who was in the aircraft flying above the BA jet."
He added: "Our pilots are highly trained and they carried out their training correctly here."
BA said the Federal Aviation Administration was now looking into the incident.
The activation of a jet's TCAS (Traffic alert and Collision Avoidance System), which monitors airspace around an aircraft independently of air traffic control, is extremely rare, BA said.
