The Boeing 777-300 (extended range) aircraft took-off from Delhi at 6:50 am. Full emergency was declared at the airport when the pilot informed the Air Traffic Control about the smoke alarm. The measures included stationing of fire brigades, ambulances, ladders and other emergency equipment close to the runway to avert a possible mishap.
Emergency was declared at the airport at 7:50 am and it was withdrawn at 8:25 am, airport sources said.
"The flight has landed back safely. We have a spare aircraft which will be used to take the passengers to London. We are working on putting together the required crew complement to operate the aircraft," Air India's Northern region head D S Kohli told sources.
As soon as the aircraft landed, passengers were disembarked and engineers and technicians went onboard to investigate the cause of the smoke alarm, Kohli said.