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Flight Level or Altitude Confusion

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Article Information
Category: Level Bust Level Bust
Content source: SKYbrary About SKYbrary
Content control: EUROCONTROL EUROCONTROL

Description

Flight level or altitude confusion occurs when a pilot is cleared to fly at a particular level and correctly acknowledges this clearance, yet levels at a different flight level or altitude.

Flight level or altitude confusion is usually the result of the combination of two or more of the following factors:

  • Mindset tending to focus on two digits, e.g. “one zero” and thus to understand more easily "FLIGHT LEVEL ONE ZERO ZERO" when the clearance was to FL110;
  • Subconsciously interpreting a request to slow down to 250 kt463 km/h <br />128.5 m/s <br /> as a clearance to descend to FL100.

A common example of this is confusion between FL 100 and FL 110 (i.e. the pilot is cleared to fly at FL 110 but levels at FL 100, or vice-versa).

ICAO standard phraseology is "FLIGHT LEVEL ONE ZERO ZERO" and "FLIGHT LEVEL ONE ONE ZERO";

Alternative non-standard phraseology used with success by a number of European air navigation service providers (ANSPs) is "FLIGHT LEVEL ONE HUNDRED", and some states have extended this phraseology to include "FLIGHT LEVEL TWO HUNDRED" and "FLIGHT LEVEL THREE HUNDRED".

Similar confusion can occur at other flight levels or between altitudes, although it is much less common and FL100/110 confusion is both the most common and the most hazardous flight level confusion seen in Europe and North America.

Solution

Sound Standard Operating Procedures (SOPs), especially with regard to:

  • Adherence to the pilot-controller confirmation/correction process (communication loop); and,
  • Cross-checking between flight crew to ensure that the selected altitude is the cleared altitude.

Related Articles

Further Reading

HindSight Magazine
  • HindSight 10: The tenth edition of HindSight, titled "Level Bust or... Altitude Deviation ?", published in December 2009, contains a variety or articles addressing different aspects of the Level Bust issue. These and other Level Bust products are listed in the article Level Bust Products