Problems for Boeing's Dreamliner aircraft were mounting yesterday, with worries the fleet could be grounded for an unprecedented second time.
Heathrow, meanwhile, was returning to normal following a day of travel chaos after a fire on one of the planes on Friday afternoon.
Company investigators are still trying to find out what caused the flames on the Ethiopian Airlines Boeing 787, prompting the airport to close both runways on Friday.
No one was on board the plane but the disruption affected about 80 arrivals and departures, causing three-hour delays and the cancellation of nearly 30 flights. Another 42 were cancelled yesterday as planes were "reshuffled" during the busy holiday season.
The airport said flights were expected to return to normal today, but the fire has raised further concerns about the aircraft's safety. The UK Air Accidents Investigation Branch, which reports to the Department of Transport, is leading the fire investigation.
A Boeing statement said: "[We have] a team working in support of UK authorities and Ethiopian Airlines, to determine the cause of the 787 event at Heathrow." But this did little to stop shares in the company, which had been up 40 per cent since March, sliding 7 per cent at one point on Friday.
The Dreamliner, which carries about 250 passengers, was unveiled as the world's most eco-friendly aircraft. Its use of carbon fibre makes it 20 per cent more fuel-efficient than comparable planes. It was supposed to enter service in 2008, but testing problems meant the first commercial flight, by Japan's All Nippon Airways, did not get off the ground until three years later.
The aviation industry will be monitoring Boeing's latest investigation closely. Initially, there were concerns that Friday's fire was caused by the same lithium-ion battery problem that grounded the entire Dreamliner fleet of 50 planes at the start of the year. But last night investigators said early indications were that the fire was not near the batteries.
After two fires in January, new batteries were eventually fitted and given more protective casing, which led to the planes resuming service in April. However, last month, Boeing's chief executive, Jim McNerney, admitted experts did not know what caused the problems in January.
Zafar Khan, an analyst at Societe Generale, said if the battery was again found to be the cause of the fire it would have a massive impact on Boeing, which, with more than 930 Dreamliner orders to fulfil, has staked much of its future on the plane.