Level busts in the UK have reached record levels in the first few months of this year, according to a report by the UK Civil Aviation Authority safety regulation group (SRG).

The study also revealed that level busts, the term for incidents where aircraft climb or descend through the altitude to which they have been cleared by air traffic control, resulting in the loss of ATC separation, increased at a higher rate in 1997 than in both the two previous years.

In a continuing campaign to counteract the level bust phenomenon, the SRG has published an analysis of occurrences in UK airspace and has commissioned an independent project to uncover the reasons why the mistakes occur.

The overall trend in level bust reports has been upward for the years analysed (1992-7), the SRG says. In addition, the reports for the first four months of 1998, at 138, are "-higher than they have ever been", and have shown a steep month-on-month increase at a time of the year when the frequency normally tends to decline.

In the years 1995-7, the annual numbers of level bust reports were respectively 142, 171 and 252 and, in the same years, the numbers of level busts which caused loss of ATC separation were respectively 45, 45 and 79. The CAA says: "It is difficult to say whether this is due to more diligent and self-aware reporting, or whether there is a genuine deteriorating trend."

The major cause of level busts is "-pilots not complying with correctly read-back ATC vertical clearances," says the study.

The SRG report has analysed the incidents by aircraft type, factoring the figures for the numbers of each type involved. Those most likely to be involved are, in descending order, the Boeing 747, British Aerospace 146 and Airbus A320.

Source: Flight International