The air traffic control failure which led to a spate of flight cancellations was caused by flight data received by National Air Traffic Services (Nats), with both primary and back-up systems responding by suspending automatic processing, chief executive Martin Rolfe said.
There are no indications that the failure was caused by a cyber-attack, he added in a statement released on Tuesday.
Mr Rolfe also wanted to “reassure” people that all Nats systems have been running normally since Monday afternoon to support airline and airport operations.
He said: “Very occasionally technical issues occur that are complex and take longer to resolve.
“In the event of such an issue our systems are designed to isolate the problem and prioritise continued safe air traffic control.
“This is what happened yesterday.
“At no point was UK airspace closed but the number of flights was significantly reduced.
“Initial investigations into the problem show it relates to some of the flight data we received.
“Our systems, both primary and the back-ups, responded by suspending automatic processing to ensure that no incorrect safety-related information could be presented to an air traffic controller or impact the rest of the air traffic system.
“There are no indications that this was a cyber-attack.
“We have well established procedures, overseen by the CAA, to investigate incidents.
“We are already working closely with them to provide a preliminary report to the Secretary of State for Transport on Monday.
“The conclusions of this report will be made public.”