What is Level Bust?

Hello, in this article, we will talk about what the term “Level Bust” means and why these events are experienced.

Based on Eurocontrol definitions, the term level bust is as follows; Vertical deviation of more than 300 feet from the level instructed by ATC. This limit has been reduced to 200 feet in RVSM airspace. Although this is generally accepted, some authorities accept only 300 feet or more as Level Bust.

level bust

The level bust is a potential cause of serious aviation hazards and occurs when flying at the FL required for safe separation is not achieved. In such cases, the separation between aircraft may be impaired, or the separation between aircraft and terrain may be impaired.

There are several things that can contribute to level busts, including:

  • Pilot error: This can be due to factors such as fatigue, distraction, or misreading instruments.
  • Incorrect altimeter settings: If the altimeter is not set correctly, it can give the pilot a false indication of the aircraft’s altitude.
  • Communication errors: Misunderstandings between the pilot and ATC can also lead to level busts.

ATC – Pilot Communication

According to the FAA and US Airlines analysis results, approximately 70% of Level Bust incidents occur due to faults in pilot-ATC communication. From this point of view, it is crucial to act in accordance with the rules of ATC Pilot transmission, use standard phraseology, rely on read-back procedures, and control the frequency health.

ATC-Pilot Radio check
ATC-Pilot Radio check

In addition, situations such as SID, Star operations, Autopilot problems, and Altimeter adjustment problems are some factors that cause Level Bust.

Another reason for these events is the late FL instructions given by ATC. During a descent or climb of an aircraft, late instructions are executed after being read-backed by the pilot. In addition, variables such as the climb rate and speed of the aircraft also affect the realization of the desired instruction. In such cases, the aircraft may not hold the desired level.

Reducing Level Bust

Many studies are being carried out to reduce these events; the most important is personnel training. Some airlines have developed level/altitude awareness programs. It is crucial to follow the rules in the use of standard phraseology and ATC Pilot conversations. If a drawn SID or Star contains rules and maneuvers that tends to cause Level Bust events due to its structure, editing these charts can also be considered. In addition to these, technical problems arising from the aircraft, even if it is a rare cause, should be emphasized, and necessary measures should be taken to prevent them from happening again.,


  1. SKYbrary Article: https://skybrary.aero/level-busts-skyclip
  2. SKYbrary Products (includes EUROCONTROL Toolkit): https://skybrary.aero/video/level-bust-scenario-1
  3. https://en.wikipedia.org/wiki/Level_bust