What happened
On January 27, 2014, at approximately 11:18 p.m. PST, a General Atomics MQ-9 unmanned aircraft system, registered as CBP159, was intentionally ditched 23 miles west of Point Loma, California. The flight was operating under instrument flight rules within Warning Area W-219 under visual meteorological conditions.
Approximately one hour before the ditching, the aircraft experienced a generator failure. Following audible alarms and various voltage and power system warnings, the pilot reversed course and performed the Dual Generator Failure Checklist. Despite multiple attempts to reset the generator, the system remained inoperable. The crew determined that the remaining battery power was insufficient to reach the nearest recovery site at Fort Huachuca, Arizona, without flying over populated areas.
To avoid populated areas, the crew proceeded to a Flight Termination Point (FTP) on the eastern side of W-291. During the descent toward the FTP, the aircraft experienced a loss of link at approximately 600 feet MSL due to a low voltage condition that triggered an automatic reset of the Interim Link Manager Assembly. After two minutes, the crew re-established the command link and positive control. The pilot then maneuvered the aircraft to the FTP, stopped the engine, and completed the ditching. The aircraft impacted the water approximately 1.7 miles north of the FTP, resulting in the destruction of the aircraft. There were no injuries.
The investigation
The investigation focused on the sequence of electrical failures. The operator reported that the aircraft was at FL280 when alarms indicated the 28 V bus voltage was approaching its lower limit, accompanied by payload shed warnings. The crew maintained electrical power for control by leaving most electrical equipment active during the ditching process. The investigation also noted that the loss of link during the descent was caused by a low voltage condition affecting the Interim Link Manager Assembly.