Accident Overview
On June 4, 2012, at approximately 0645 Pacific daylight time, a Hiller UH-12B helicopter, registration N93467, impacted fruit trees in an orchard near Pasco, Washington. The commercial pilot, the sole occupant, was not injured. The helicopter, operated by Larsen Helicopter Operations, sustained substantial damage. The flight was conducted under 14 Code of Federal Regulations Part 91 for fruit orchard drying operations in visual meteorological conditions. The pilot had departed Tri-Cities Airport in Pasco about 0615; no flight plan was filed.
Pilot Narrative
According to the pilot, after completing drying of one orchard section using the main rotor downwash, he ascended to an estimated 100 to 150 feet above the trees to survey for obstacles in a separate section he planned to dry next. During the subsequent descent to operating altitude, he observed that main rotor rpm, initially in the lower part of the normal range, began to decrease. He added throttle but the rpm continued to decay. He then lowered the collective in an attempt to recover rotor rpm, but by that time he was approximately 20 feet above the trees. He applied full throttle and attempted to pump the collective, yet the rpm continued to decay. Maintaining a level attitude and using forward airspeed, he guided the helicopter between two rows of trees, where it settled upright to the terrain. Just before touchdown, both the main rotor and tail rotor contacted the fruit trees.
Post-Accident Examination
A Federal Aviation Administration inspector performed an initial examination at the accident site. The helicopter was subsequently moved to AvTech Services in Maple Valley, Washington, where an NTSB aviation safety investigator examined the engine and airframe. Examination confirmed spark at all spark plug leads, compression in all cylinders, gear continuity to the accessory section, and normal wear on spark plug electrodes. The carburetor bowl contained a small amount of fuel consistent with aviation low lead; a small sliver of metal was found in the inlet finger screen, but no preimpact anomalies or malfunctions were evident. The oil filter showed no metal or debris, and internal gearing appeared well lubricated with no signs of thermal distress. Due to impact damage to the crankcase, the engine could not be test run, but no evidence of any preimpact malfunction of the airframe or engine was found. The pilot reported that during engine start, battery voltage may have been insufficient, but he noted no unusual engine sounds or performance irregularities throughout the flight.