REVEALED: Titsup flight plan mainframe borks UK air traffic control

The clock was ticking

During Friday's incident, NATS engineers actually got the flight data processing system back up and running within 15 minutes, one source told us. Once the flight data system was operational again, the information couldn't be sent to the central flight server in a usable format because the link had gone down at the same time as the server, and was proving impossible to immediately reconnect.

It's not clear what caused these problems. The ATC computer network originally ran on a token ring network, but in the last couple of years this has been swapped out for a standard Ethernet setup.

"Today's system outage was in reality somewhere in the region of 15 minutes. Unfortunately that's about seven minutes too long," one source said. "If the recovery had been faster this wouldn't have even registered on the news."

As a result of the extended delay the whole system went into a safety lockdown, albeit briefly. But the knock-on effects were huge. Planes are diverted to other airports, which completely screws up airlines' schedules as ongoing flights can't pick up passengers, fuel, and vaguely revolting food for the cattle-class citizens.

Scene at @HeathrowAirport this evening during flight disruption [apologies - earlier picture was not Heathrow today] pic.twitter.com/jfoEMlGA2K

— BBC Breaking News (@BBCBreaking) December 12, 2014

The alternative is having thousands of people on hundreds of aircraft flying over the nation's capital in an unsafe manner. Under the circumstances, NATS had no hesitation shutting the system down.

This evening, UK Transport Secretary Patrick McLoughlin said: "Any disruption to our aviation system is a matter of the utmost concern, especially at this time of year in the run up to the holiday season. Disruption on this scale is simply unacceptable and I have asked NATS for a full explanation of this evening's incident. I also want to know what steps will be taken to prevent this happening again."

When we explained what we knew to NATS, a spokesman confirmed that Friday's shutdown stemmed from "problem with the system delivering flight data to air traffic control."

"The issue is still being investigated but all systems are now back up and running, and we now need to ramp air traffic levels up slowly. Thankfully now all systems are back up and fully operational." ®