LAX00GA114 · Bell OH-58C

The helicopter hit a trailer and the ground during an autorotation precipitated by pilot perceived malfunctions in the electrical and hydraulic systems during cruise. A city police department operated the helicopter for law enforcement patrol missions. After exiting an orbit around a ground situation, the crew saw the low rotor rpm warning light flash on, then back off, then on again. Normal rotor and engine rpm was shown on the tach. They were only 3 miles from their airport base and the pilot decided to return there. The low rotor warning light began to flash on and off, with an increasing frequency until it was steady. Suddenly all the cockpit warning and caution lights illuminated, both on the eyebrow panel and center pedestal panel. The hydraulic system also turned off and the pilot had to resort to manual force on the flight controls. The pilot checked the engine and rotor gages and noted that the rotor needle was pointing off scale high; however, neither crewmember heard any change in the engine and rotor sounds. The observer reported that he believed they lost their radios and exterior lights at this time and also said that the engine and rotor tach needles were married together at 100 percent until the autorotation. The pilot was on an extended final approach to the runway and helicopter control was becoming difficult. Suddenly, an airplane appeared on base leg to the runway and the pilot had to maneuver to avoid a collision. With the control difficulties and uncertainty about what was happening to the helicopter, the pilot decided to autorotate to a clear area in a schoolyard. The night sun spotlight failed during the autorotation and the pilot cleared a building but could not avoid a parked trailer that he had not seen before. The helicopter collided with the trailer, then the ground, and rolled over. The hydraulic system solenoid valve is electrically operated and it takes electrical power to close the valve and turn off the hydraulics; the valve fails to the open position when electrical power is lost. Post accident testing of the hydraulic system found normal operation. The complete electrical system wiring was traced from the generator and battery to the ground points on each circuit, with no discrepancies found. The main rotor tach drive and the cockpit gauge were functionally tested. No like events were found during searches of the historical records for the US Army, Bell Helicopters, or in the FAA SDR database. Bell Helicopter opined that an almost complete electrical system voltage spike/surge simultaneously in a large number of circuits would be required to replicate the event as described by the crew.

Verbatim NTSB analysis and probable cause from the NTSB dataset