LEVEL BUSTS

This is a reprint of AIC 94/2000.
The original can be found here

AIC 67/1996 (Pink 124) described the results of a safety review, conducted by the Civil Aviation Authority, on the subject of level busts recorded in UK airspace during 1994.  The information contained in this AIC is an update based on an analysis of all level busts in UK airspace reported between 1 January and 31 December 1999.

A total of 455 level busts (i.e. any unauthorised vertical deviations of more than 300 feet from ATC assigned levels) were recorded during this period.  The analysis identified the most common causal and contributory factors associated with each occurrence.  These included:

The sum of the figures in the above breakdown of factors exceeds the total of 455 level busts, as each occurrence could involve more than one factor.  Level busts occurred most commonly during the climb phase of flight, at between 3000 feet and FL120 and in TMA airspace. The split between UK and foreign operators was close to 50:50.

The Civil Aviation Authority continues to have concern about these potentially hazardous occurrences. The majority of the factors identified in the above table are manifestations of human errors in operating techniques or in communications areas and can be addressed by the use of already established good practice in the use of appropriate and standard RTF phraseology and techniques, together with adherence to established flight deck drills and ATC procedures.

The purpose of this circular is to draw attention to the following:

• Aircraft operators’ attention is drawn to Flight Operations Department Communication 2/97 which provides information on good practice regarding flight crew drills.

• Aircraft operators and air traffic control providers are urged to continue to highlight level busts in their ongoing training arrangements and are requested to bring this circular to the attention of their flight crews, air traffic controllers and other staff who are involved in the training and briefing of these groups.

• Flight crews who are uncertain of the exact content of an ATC instruction should not rely on a readback for confirmation purposes, instead they should query that instruction on the RTF.

• Air traffic controllers should actively listen to readbacks of instructions to ensure that the readback matches the original instruction and that they do not simply “hear” what was expected when an error is made.

• Air traffic service providers should take steps to ensure that sector and other airspace capacities are set such that there is adequate time available to flight crews and controllers to allow safe and unrushed interchanges via RTF.

The awareness campaign instituted by the Level Bust Working Group will continue for the time being and aircraft operators and ATC providers are asked to continue providing their valuable support by continuing to encourage the full reporting of level bust incidents through Air Safety and MOR schemes.