Air traffic controllers 'repeatedly misread altitude'

Controllers have "repeatedly" misread the altitude of aircraft by thousands of feet because of badly designed screens at the new £623m control centre at Swanwick, it was claimed yesterday.

In at least one case, an aircraft was sent into a sector at the wrong altitude, although the mistake was spotted, according to a confidential submission by a controller to management at National Air Traffic Services (Nats).

Air traffic staff have also registered "great difficulty" in distinguishing Glasgow from Cardiff because the codes for cities – EGPF for the Scottish city, EGFF for the Welsh capital – are so similar and the print size so small. One controller had initially treated an aircraft as if bound for Cardiff and then discovered it was headed for Glasgow. Another report refers to a controller "mixing up" FL360 (36,000ft) and FL300 (30,000ft).

Although the partly privatised company claims that none of the complaints by controllers was safety related, a letter dated 18 January from the Health and Safety Executive said the design defects "may have implications for safety". The controllers who filled in the "feedback" forms also indicated that safety might be impaired, according to the magazine Computer Weekly.

A report from the Health and Safety Executive has pointed out that the screens do not meet Nats' own specifications. The HSE document says the print size on some screens is too small and the figures 0.8 and 6 can be difficult to distinguish.

Screens were designed to be read from 50cm away but many controllers sit about 70cm away, it says. The magazine reported that Swanwick controllers had "repeatedly" misread the altitude displayed on a screen by thousands of feet.

Computer problems at Swanwick delayed the opening of the new Swanwick centre in Hampshire from 1996 to January this year. Electronic glitches have caused flight delays and cancellations three times over the last two months. Last Friday computer problems led to hours of chaos at all of Britain's major airports.

Nats said the problems had been with planners who did not handle aircraft "live" on their screens. It said there had been no "safety-related incidents" and the CAA had said repeatedly that Swanwick was "safe". A spokesman added: "An improved display has been developed and prototype testing is due to begin shortly."