Crewmember fatigue can be defined as:

• A physiological state of reduced mental or physical performance capability resulting from sleep loss or extended wakefulness, circadian phase, or workload (mental and/or physical activity) that can impair a crew member’s alertness and ability to safely operate an aircraft or perform safety related duties.

Fatigue is a major human factors hazard because it affects most aspects of a crewmember’s ability to do their job. It therefore has implications for safety. ICAO defines a Fatigue Risk Management System (FRMS) as:

• A data-driven means of continuously monitoring and managing fatigue-related safety risks, based upon scientific principles and knowledge as well as operational experience that aims to ensure relevant personnel are performing at adequate levels of alertness.

An FRMS aims to ensure that flight and cabin crew members are sufficiently alert so they can operate to a satisfactory level of performance. It is a set of guidelines aimed at reducing fatigue-induced safety risks and considers additional factors such as the circadian rhythm, the importance of adequate sleep within the rest period, and the unique properties of the individual operation. FRMS is based on computer models which anticipate the expected performance capability of a person from his/her sleep/awake history. Such models must be continuously updated by analyses of data and reports. The quality of the FRMS depends on its ability to learn. The term used for this kind of safety culture is “learning culture”.

It is also dependent on the willingness of aircrew to report fatigue-related issues and in a culture where crew members are encouraged to report safety risks. However, such safety cultured is named “just culture” and not “non-punitive culture”.