Delays at Heathrow and Gatwick are expected from today as a new digital air traffic information system is implemented by the National Air Traffic Services (Nats).
The new technology is being introduced because the old paper-based system for recording instructions passed to pilots cannot cope with increased demand.
Nats says the new electronic tool, known as EXCDS, will improve efficiency and enable it to handle forecast demand in the future. It replaces a manual system used for the past 40 years.
As the new system is being introduced NATS said it will reduce the volume of air traffic on the southeast of England as controllers get used to it.
Nats, which is based in Hampshire, told the BBC it will be controlling the amount of traffic at Heathrow at Gatwick for two days.
A spokesman said: “It’s very difficult to predict exactly what that delay will be – there are many other factors like the weather and industrial action in France.
“Broadly speaking, as a rough rule of thumb, we anticipate that where aircraft are delayed – going into Heathrow, for example – the average delay per aircraft will be about 20 minutes.
“It’ll be about half of that at Gatwick – about 10 minutes.”
Night time curfews for landing and departing aircraft will also be relaxed after Nats requested permission for some services to operate slightly earlier and slightly later than usual.