Expansion at Heathrow Airport will bring economic benefits to the UK economy, Willie Walsh, ceo of BA, said.
Mr Walsh said Heathrow was the main airport for business travellers in London and the only viable one for long haul passengers.
He said that if the proposed third runway was built, it could add a further 75 destinations to the 180 already served by the airport.
But without this development, Heathrow could lose 30 destinations.
Mr Walsh added: "If Heathrow's international connectivity continues to decline, UK-based businesses will lose competitiveness and be forced to consider relocating abroad," he said.
"Meanwhile, businesses in the UK regions will find it increasingly difficult to attract inward investment or promote their products in new overseas markets.
"Good air links are essential to success in a global economy."
On environmental issues, Mr Walsh said that by the time the third runway was built, "aviation emissions will be capped by the European Union carbon trading scheme."
BA, in a press statement, also said that delays caused by bad weather at Heathrow could be cut by two thirds if "mixed mode" where a runway is used for both landing and take off were used.
Paul Ellis, BA's infrastructure manager, said: "Years of practical experience of runway operation at Heathrow and Gatwick has shown conclusively that mixed mode operation provides much better protection against delays when weather conditions are difficult.
"The introduction of mixed mode at Heathrow would be a real bonus for passengers.
"We estimate that it would cut weather delays by up to two thirds from Day One and provide much greater reliability throughout the timetable."
Sir Richard Branson, president of Virgin Atlantic, also joined the call for a third runway.
He said that multi-national businesses were "likely" to move out of London if the expansion did not go ahead.
In its submission to the UK government's consultation process on the planned extra runway, Sir Richard said: "With more runways being built in other European cities, such as Frankfurt, it is more important than ever that London expands its capacity.
"Business travellers need an airport that flows seamlessly, not one that seizes up due to lack of space on the runways.
"Businesses will move their global headquarters to elsewhere in Europe, and they will take thousands of jobs with them if a third runway fails to be built at Heathrow.
"Routine delays and circling overhead by all airlines, manoeuvres that simply increase pollution levels, will only be stopped with extra capacity."
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