Dual use of Heathrow’s twin runways is to be introduced for a four-month trial period.
The runways are normally restricted to either take-off or landing and switch each afternoon to give residents respite from aircraft noise.
Under the trial period, dual use of the runways can be deployed when an aircraft faces a 10-minute wait to land or take off and if 30% of all flights are delayed by more than 15 minutes.
The average delay for flights at the London hub is 12 minutes.
The trial finishes on February 29 while a second will run from July 1 until September 30, 2012.
The trial, recommended by the Department for Transport, will be overseen by the Civil Aviation Authority.
Heathrow owner BAA said there may be fewer late-running flights after 10:30pm as a result.
Emissions could also be reduced as well as the aircraft will spend less time in holding patterns waiting to land.
The number of flights will remain capped at 480,000 aircraft movements a year.