Accident Overview
A certificated helicopter flight instructor was conducting an introductory flight instruction lesson under Title 14, CFR Part 91 with a prospective student. The helicopter crashed in a residential area, coming to rest between two houses. The impact damage was consistent with a high-speed, fuselage-level, vertical descent.
Witness Observations
A witness located about one mile south of the accident site reported seeing the helicopter pass overhead at an estimated altitude of 1,000 feet above ground. Shortly after, the witness heard a "pop," followed by the helicopter initiating a shallow, controlled left turn. Two or three additional popping sounds were heard. The helicopter then began descending rapidly while spinning counter-clockwise. As the descent rate increased, the main rotor blades stopped turning, and the helicopter entered a vertical descent. The witness noted that no engine sounds were audible during the final descent.
Postaccident Inspection
A postaccident examination of the engine core and airframe found no evidence of preimpact anomalies. Impact damage prevented functional testing of the engine's carburetor and ignition wiring harness assemblies.
Pilot Background
A review of the accident pilot's historical training records revealed a series of failed check rides and overall substandard performance. Interviews with previous and prospective employers indicated that the pilot had been dismissed or not hired due to a lack of academic or flight skills.
Emergency Procedures Reference
The FAA-approved flight manual for the helicopter includes emergency procedures for engine failure. The required actions at the first indication of engine failure are: lower the collective immediately to maintain rotor rpm and enter a normal autorotation, then establish a steady glide at approximately 65 knots. The helicopter manufacturer published a safety notice addressing low rotor rpm conditions. It states that a failure to maintain rotor rpm is a primary cause of accidents in light helicopters. The notice emphasizes that pilots must be conditioned to instantly add throttle and lower the collective to recover rpm. It further warns that pulling up on the collective without lowering it can lead to rotor stall, causing the rotor to either blow back and sever the tail cone or stop flying, resulting in a high-rate descent. The safety notice advises that, regardless of the cause of low rotor rpm, the pilot must first roll on throttle and lower the collective simultaneously to recover rpm before troubleshooting. In forward flight, applying aft cyclic to reduce airspeed can also aid in rotor rpm recovery.