Just months after opening the long-awaited £623m Swanwick air traffic control centre, the National Air Traffic Service (Nats) suffered an embarrassing computer crash at one of its other sites.
Last week's software glitch at West Drayton, the second in a matter of weeks, was splashed across the pages of the national newspapers, raising further questions about whether the part-privatised air traffic service can run reliable IT systems.
West Drayton is the base for Nats' London Terminal Control Centre and oversees aircraft flying at less than 24,000 feet in the London area. However, it works closely with the Swanwick centre, which is responsible for most of the airspace over England and Wales.
Nats said the problems last week were caused by a software glitch on West Drayton's Flight Data Processing System (FDPS). This produces flight progress strips, which have crucial information such as radio call signs, aircraft type and destination, for air traffic controllers at West Drayton and Swanwick.
When the system failed at 6.05am on 10 April, staff had to write this information by hand, which created disruption to the air traffic network.
A Nats spokesman said the computer was re-started at 6.21am and the system was operating at full capacity by 8.30am. He was keen to point out that controllers remained in contact with aircraft at all times. "There was no interruption to the radar screens or to the radio contact with the pilots," he said. Controllers could see where the aircraft were and talk to the pilots, he added.
The problems, however, raise questions about the software employed by Nats. Although the affected FDPS at West Drayton runs on two IBM S/390 mainframes which are only six months old, it uses software that was originally developed in the 1970s.
The Nats spokesman said the program, which is used in several countries, had been updated many times but said, "We are now conducting a technical examination of the software to pinpoint the problem and eliminate it."
Nats has narrowed the fault down to a small area of the software and is examining it in great detail, he said.
The problem was restricted to West Drayton, Nats insisted. The spokesman said, "It had an effect on Swanwick only because it provides information for Swanwick. The FDPS at West Drayton is not the same as the new technology system we employ at Swanwick."
But Nats has been here before. In June 2000, the FDPS crashed twice. The second time the system tried to reboot in a "multiple start-up mode", and the problem was not resolved for nearly seven hours. Hundreds of flights around the world had to be cancelled and the journeys of thousands of passengers were severely delayed. At the time, Computer Weekly revealed that FDPS software, which is more than 20 years old, would not be replaced until 2007.
Nats said it is not reviewing the replacement date in the light of last week's outage.
Liberal Democrat transport spokesman Tom Brake called on Nats to give assurances on safety in the aftermath of the problems. "Nats must give assurances that there is no possibility that this fault has been replicated in the new system," he said. He hoped that further testing of West Drayton's flight data system would be carried out.
Conservative MP Theresa May criticised the Government. "These continuing problems for Nats raise further concerns about the consequences of Labour's flawed partial privatisation of air traffic control," she said.
But despite the disruption to airline customers, a spokesman for the Airline Group, which owns 46% of Nats, said last week's events have been blown out of proportion. "The net effect on flights was no more than a day of adverse weather conditions." The group is confident that Nats can identify the problem and ensure it does not recur.
The Airline Group spokesman said investment is available to replace old systems.
But he was unable to clarify where the investment would come from. Nats is due to receive a £60m loan from banks and the Government as it awaits the results of an application to the Civil Aviation Authority to raise its prices. Nats may face financial collapse if it is unable to increase prices, it said in its application to the authority.
Nats is fighting a case in the high court against IT services giant EDS over the computer system for its Oceanic control centre. Nats could face a £50m legal bill if it loses.