Availability is a measure of how often a system or component is in the operable and committable state when the mission is called for at an unknown (random) time. It is measured in terms of the percentage of time a system can be expected to be in place and working when needed, or mission available rate (MAR) in percent.
Class A Mishap Rate is the number of accidents (significant aircraft damage or total loss) occurring per 100,000 hours of fleet flight time. In cases where a UA fleet has not accumulated this amount of flying time, its MR represents its extrapolated losses to the 100,000 hour mark. It is expressed as mishaps per 100,000 hours. It is important to note that this extrapolation does not reflect improvements that should result from operational learning or improvement in component technology.
Maintenance cancellations/aborts were broken out into failures of the aircraft’s major subsystems. Use of these failure modes lead to a higher fidelity representation of the aircraft’s reliability. In order to make uniform comparisons between systems, the following definitions were used to categorize areas of system failure leading to mission aborts or cancellations.
Power/Propulsion (P&P). Encompasses the engine, fuel supply, transmission, propeller, electrical system, generators, and other related subsystems on board the aircraft.
Flight Control. Includes all systems contributing to the aircraft stability and control such as avionics, air data system, servo-actuators, control surfaces/servos, on-board software, navigation, and other related subsystems. Aerodynamic factors are also included in this grouping.
Communication. The data link between the aircraft to the ground.
Human Factors/Ground Control. Accounts for all failures resulting from human error and maintenance problems with any non-aircraft hardware or software on the ground
Miscellaneous. Any mission failures not attributable to those previously noted, including airspace issues, operating problems, and other non-technical factors. Because operating environments are not uniform as a variable affecting the data, weather was excluded as a causal factor in this study.
Data and Trends
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