A United Airlines plane had to make an emergency landing shortly after take-off from Heathrow on Wednesday (July 30). The San Francisco-bound aircraft declared an emergency following reports of smoke in the cabin.br Flight UA949, a Boeing 777-200ER, took off at 12.23pm but stopped its climb at 15,000 feet and turned back near Milton Keynes. It is understood the crew reported a technical issue and broadcast a 7700 emergency squawk with smoke said to be visible in the cabin.