Level-bust incidents in UK airspace are continuing to increase, climbing by more than 25% last year despite concerted efforts to rein in the problem.

UK air navigation service NATS and the Civil Aviation Authority have focused on attempting to reduce level busts, the deviation of an aircraft by more than 300ft (90m) from its assigned altitude. But NATS statistics show that the number of incidents last year had exceeded 500 by the end of November. In the previous year fewer than 400 were recorded.

The CAA's Safety Regulation Group concedes that improved reporting by pilots and controllers is partly responsible for the rise, although incidents are still thought to be under-reported by 70%. Most busts occur below flight level 120 in busy terminal airspace. Assessment shows the largest contributing cause - accounting for about one-fifth of all incidents - is pilots failing to take the correct action despite correctly reading back a controller's instructions.

The CAA has released a revised "best practice" advisory, stressing caution when dealing with possible call-sign confusion or simultaneous transmissions.

Source: Flight International