§ Mr. Salter
To ask the Secretary of State for Transport, Local Government and the Regions on how many occasions in the last six months there has been a significant computer failure at National Air Traffic 53W Services leading to the disruption of aircraft movement in UK airspace; what action he is taking to prevent such failures; and if he will make a statement. 
§ Mr. Jamieson
[holding answer 17 April 2002]: This is an operational matter for NATS. I understand the position to be as follows.
There have been two occasions in the last six months, on 27 March and 10 April, when aircraft movements in UK airspace have been disrupted by unplanned computer stoppages. Both events occurred at West Drayton as a result of a software problem associated with an unusual set of circumstances connected with flight data.
NATS is conducting a full inquiry into the incidents, to establish whether further adjustments are required to ensure the long term robustness of the system.
Apart from these two incidents, NATS has experienced no significant computer failures in the last six months. Notwithstanding the incident on 27 March, the Flight Data Processing System at West Drayton achieved 99.6 per cent. availability in the year ended 31 March.