无人机系统路线图 Unmanned Aircraft Systems Roadmap(185)

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RQ-5/Hunter
Following three crashes in close succession in August-September 1995, OSD terminated the RQ-5/Hunter program after LRIP completion by deciding to not award a full rate production contract.  Seven systems of eight aircraft each were delivered between April 1995, and December 1996.  A total of 62 aircraft were built by IAI/Malat and assembled by TRW, now Northrop Grumman Corporation.  Since that redirection, however, the Hunter program has made numerous component quality related improvements and been used to demonstrate a wide variety of payloads including SIGINT, chemical agent detection, and communication relay for UA use.  It has supported National Training Center exercises and NATO operations in Kosovo, and it recently served as the surrogate TUA for the Interim Brigade Combat Team at Ft Lewis, Washington.
The acquisition of the Hunter system by the Army presents a case study in the peril of ignoring, and the benefits of overcoming, reliability problems.  During system acceptance testing in 1995, three Hunter aircraft were lost within a 3 week period, contributing to a decision to terminate full rate production. 
APPENDIX H – RELIABILITY
Page H-7
UAS ROADMAP 2005

Wanting to benefit as much as possible from its substantial investment in the Hunter, its Program Management Office and the prime contractor (TRW) performed an end-to-end Failure Mode Effect and Criticality Analysis (FMECA) and a Fishbone Analysis on each of the critical subsystems.  An interconnected network of failure analysis and corrective action boards was implemented with the authority to direct design changes to Hunter.  Failures of its servo actuators, the leading culprit for the series of crashes, were identified, and their MTBF increased from 7800 hours to 57,300 hours, a sevenfold improvement.  Other key components received focused attention including the data link and engine.
Hunter returned to flight status three months after its last crash.  Over the next two years, the system’s MTBF doubled from four to eight hours and today stands at over 21 hours.  The aircraft itself achieved its required MTBF of ten hours in 1998, and today that figure stands close to 26 hours.  Prior to the 1995 stand down and failure analysis, Hunters were experiencing a mishap rate of 255 per 100,000 hours; afterwards (1996-2005) the rate was 24 per 100,000 hours.  Initially canceled because of its reliability problems, Hunter has become the standard to which other UA are compared in reliability.
In addition to the reliability data shown in Table H-1, an in-house reliability assessment performed by the prime contractor for the period of 1995 through 2005 found an availability of 0.991.  The calculated reliability per mission was 97 percent.
The failure modes analysis in Table H-2 is built on data from December 20, 1995 to June 15, 2005.  This data shows that Hunter’s non-weather related failures were led by power and propulsion issues (38 percent). This concentration is a shift from the more evenly distributed failure mode breakout shown during a 2003 reliability assessment (2003 OSD UAV Reliability Study). This follows in the trend of the Predator and Pioneer systems, which also suffer failures due primarily to power and propulsion. The 19 percent of failures attributed to “Miscellaneous” includes malfunctions with the flight termination system and parachute aircraft recovery system.
　
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