The result of the inquiry into the need for a new airport runway in the south-east may be delayed for more public consultation.
Sir Howard Davies, the chairman of the Airports Commission, has decided to take further evidence on problems caused by air pollution.
His decision comes after a Supreme Court ruling in April, ordering the UK to do more to improve air quality.
The consultation will begin immediately and end on Friday 29 May.
The commission has already recommended three options, one of which was a new runway at Gatwick.