What happened
On August 17, 2008, a Robinson R-22 Beta II helicopter, registration N301MA, crashed near Olalla, Washington. The pilot, the sole occupant, had departed Bremerton National Airport approximately 20 minutes prior to the accident for a personal pleasure flight. The pilot's intention was to land on a newly constructed landing pad at his residence.
Witnesses observed the pilot performing several low-level passes near his home, flying at approximately 200 feet above ground level. The pilot was reportedly waiting for a passenger to arrive at the residence by car before attempting his first landing on the new pad. During these maneuvers, witnesses reported varying sounds from the engine, including a loud grinding noise and, in one instance, the engine sputtering and misfiring.
Shortly after a north-to-south pass, the helicopter descended rapidly. During the final stages of the descent, the main rotor blades struck tree limbs at a height of about 20 feet. The aircraft then struck a wooden fence before coming to rest partially inverted in a dense growth of vines. The pilot sustained 1 fatal injury.
The investigation
Investigators examined the wreckage and the engine. The engine was removed and tested on a dynamometer, where it performed normally through the entire RPM range without any identified malfunctions. The fuel system showed no evidence of contamination or water.
Examination of the mixture control cable revealed that the inner wire was not secured through the eye of the attachment bolt; instead, it was resting alongside the bolt. Laboratory analysis of the hardware indicated that the wire had been properly threaded through the bolt prior to the accident, suggesting the displacement occurred during the impact.
Findings
- The aircraft was operating in ambient weather conditions that were conducive to the formation of carburetor ice.
- The pilot failed to properly monitor the carburetor air temperature gauge and failed to use appropriate carburetor heat settings to prevent ice accumulation.
- The pilot had recently used diphenhydramine, a sedating antihistamine, though the exact level of impairment could not be determined.