Unmanned Aircraft Systems Roadmap 2005-2030 - Federation of ...

UAS ROADMAP 2005
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
Figure H-1 shows the Class A Mishap Rate per 100,000 hours versus cumulative flight hours for the
Global Hawk, Predator, Hunter, and Pioneer fleet for the period 1986 through 2003. Class A mishaps are
those aircraft accidents resulting in loss of the aircraft (in Naval parlance, “strike”), human life, or causing
over $1,000,000 in damage 2 . These data show a mishap rate (i.e., Class A accidents per 100,000 hours of
flight) of 20 for Predator, 47 for Hunter (24 since the major reliability improvements in 1996), 88 for
Global Hawk, 281 for Pioneer, and 191 for Shadow. For comparison to two manned military aviation
mishap rates, the U-2 and F-16 have cumulative Class A mishap rates of 6.8 and 4.1 per 100,000 hours,
respectively. Comparing to non-military aircraft, general aviation suffers about 1 Class A mishap per
100,000 hours, regional/commuter airliners about a tenth of that rate, and larger airliners about a
hundredth of that rate.
With the exception of Pioneer and to a lesser extent Shadow, these statistics make it apparent that the
reliability of UA is tracking that of early manned military aircraft, and maturing to approach an equivalent
level of reliability to their manned military counterparts. Specifically, the early Pioneers (as discussed
later in this appendix) had an analog air data system, problems with ship-board EMI, and generally
suffered from poor design practices. (A planned conversion to a more reliable engine for the Pioneer
never took place.) Compared to this low benchmark, the Hunter program has seen continuous reliability
enhancements from efforts initiated in the mid-1990’s to improve hardware and maintenance. Not
surprisingly for the higher-end systems, the Predator has enjoyed relatively high and stable reliability
2 Per OPNAV Instruction 3750.6R, “Loss of a UAV is not a Class A unless the cost is $1,000,000 or greater.” All
Pioneer mishaps discussed are therefore Class B Mishaps.
APPENDIX H – RELIABILITY
Page H-2