Early morning flights into and out of London airports (Heathrow, Gatwick and Stansted) were delayed following a post-maintenance planning system failure at National Air Traffic Control (NATS).
The internal flight planning software normally uploads the plans to the controllers' displays before each plane arrives or leaves, but late last night the software stopped automatically uploading, after the routine maintenance.
The problems delayed flights to and from the airports for up to an hour. Staff were left manually inputting flight plans, until the system was fixed at 8.30 this morning.
A spokesperson at NATS said overnight routine maintenance had taken place and that the system had not worked fully afterwards. But she said it was "too early" to ascertain further details.
NATS, which is currently trialling cloud computing with 300 staff under its Future Workspace programme, said the new system did not play a part in the problem because they did not concern front line air traffic control operators.