The UK government has once again delayed a decision on increased runway capacity in south-east England.
Patrick McLoughlin, Secretary of State for Transport, said further environmental research needs to be carried out.
A decision is anticipated to "conclude over the summer", he said.
"The case for aviation expansion is clear – but it's vitally important we get the decision right so that it will benefit generations to come," McLoughlin said.
"We will undertake more work on environmental impacts, including air quality, noise and carbon. We must develop the best possible package of measures to mitigate the impacts on local people.
"We will continue work on all the shortlisted locations, so that the timetable for more capacity set out by Sir Howard is met. At the first opportunity I will make a statement to the House to make clear our plans."
Reaction to the much-leaked non-decision was swift.
Stewart Wingate, CEO of rival bidder London Gatwick, hailed the delay as "a defining moment in the expansion debate".
He said: "There is now a clear choice facing Britain — growth with Gatwick or inertia at Heathrow with an illegal scheme that has failed time and time again.
"We have always maintained that this decision is about balancing the economy and the environment. Expansion at Gatwick would give the country the economic benefit it needs at a dramatically lower environmental cost.
"We are glad that the government recognises that more work on environmental impact needs to be done. Air quality, for example, is a public health priority and obviously the legal safeguards around it cannot be wished away.
"Even Heathrow's most vocal supporters must now realise a third runway at Heathrow will never take off as the environmental hurdles are just too high. If they want Britain to have the benefits of expansion and competition they should now look to Gatwick."
IAG chief executive Willie Walsh criticised the delay as "party politics taking precedence over what is best for the economy".
He said: "If a runway is built at Heathrow, there must be a fundamental review of the costs. Only around one per cent of the £17.6 billion is for the actual runway and more than £800 million is for a new car park. No wonder Heathrow makes more money than any other airport group in the world.
"Terminal 5 cost £5.6 billion in today's money to build yet the new terminal, which will handle the same number of passengers, is slated to cost more than £8 billion. If Britain is to develop new infrastructure, it should be efficient and cost-effective."
Mark Tanzer, ABTA (Association of British Travel Agents) chief executive, said: "It is deeply disappointing that the decision on whether to go ahead with a third runway at Heathrow has been delayed yet again.
"The report published by the Airports Commission in July clearly recommended expansion at Heathrow following three years of fair, transparent, and thorough processes and consultations.
"Whilst ABTA agrees it is essential that environmental impacts must be minimised and mitigated, clear and decisive action is needed now. Failure to act will only lead to further significant damage to the UK economy."
Declan Collier, CEO of London City airport, said: "Even if a new runway were to be approved now, it is at least a decade away from being delivered, and today's announcement means it is now even further away from becoming a reality.
"LCY can provide more capacity within two to three years – it already has permission to operate more flights than it does today – and yet it has been prevented from doing so...
"The London Borough of Newham understood the benefits and decided to grant permission for LCY's development plans, the Mayor of London's own planning officers recommended the same, but the Mayor himself acted alone to refuse the plans.
"London City is appealing against the Mayor of London’s decision and the appeal will be heard at a public inquiry next spring."
Dale Keller, chief executive of BAR (Board of Airline Representatives) UK, said: "Our airline members are dismayed that the uncertainty and indecision over expanding Heathrow is set to continue into next summer for what appears to be local political reasons, rather than the need for further environmental analysis.
"The Airports Commission spent almost three years - and £20 million, to produce the most detailed independent report of its type ever commissioned. It therefore seems inconceivable that the government has had insufficient time, or a lack of information, to make the decision it long promised."
Dr Volodymyr Bilotkach, a senior lecturer in economics and aviation industry expert at Newcastle University Business School, said: "It is clear that additional runway capacity is needed in the south-east of England as we will soon reach the point where current capacity is insufficient and the economy will inevitably suffer as a result.
"Unreliable air services make London, and the UK as a whole, a less desirable location for businesses."
In October, London Heathrow released images of what a third runway at Heathrow would look like (see news, October 5).