Definition

Level Bust is defined as any unauthorised vertical deviation of more than 300 feet from an ATC flight clearance.

Within Reduced Vertical Separation Minima (RVSM) airspace this limit is reduced to 200 feet. (EUROCONTROL - HEIDI)

Definitions applied by other organisations are similar but sometimes refer to a deviation of 300 feet or more.

The level bust issue only relates to aircraft in controlled airspace or a designated ATZ outside controlled airspace and under either radar or procedural ATC control.

Description

A Level Bust or Altitude Deviation occurs when an aircraft fails to fly at the level to which it has been cleared, regardless of whether actual loss of separation from other aircraft or the ground results.