What happened
While performing a landing at an unprepared sand pad near a creek, the pilot of a Eurocopter AS3/30B was on final approach at approximately 20 feet above the ground. During the attempt to reduce the descent rate, the pilot heard the low rotor horn indicating a drop in rotor speed. Despite efforts to use the collective, the pilot could not arrest a rapid increase in the rate of descent, resulting in a hard landing.
Upon impact, the helicopter's tail stinger and right skid struck the ground, causing the tail boom to separate and the forward section of the right skid to break. The aircraft pitched nose-down and rolled onto its right side. During the rollover, the weight of the four passengers shifted, causing the right rear cabin door to slide off its track. One passenger was partially ejected and pinned between the door and the fuselage, though the other occupants managed to lift the airframe to rescue them. All occupants were transported to a local hospital for treatment.
The investigation
Investigators examined the engine's bleed valve, an electro-pneumatic component designed to prevent compressor stalls. Testing revealed the valve operated erratically and was prone to closing at a slower rate than intended. This delay prevented the engine from reaching full power, resulting in a loss of approximately 63 shaft horsepower.
Technical analysis determined the valve had been incorrectly assembled during manufacturing, specifically regarding the indexing of the rack and pinion gearing. Additionally, dust and sand contamination from normal operations had accumulated within the valve, contributing to its erratic behavior. The investigation also noted that while the passengers were wearing lap belts, they were not utilizing the provided shoulder harnesses, which may have influenced their movement during the roll.
Findings
- The engine bleed valve malfunction prevented the engine from developing sufficient power during a critical phase of flight.
- The pilot's attempt to arrest the descent by applying collective pitch led to over-pitching the main rotor blades, further reducing rotor RPM.
- The valve's failure was caused by a combination of incorrect manufacturing assembly and internal contamination.
- The passenger's injury was exacerbated by the lack of use of shoulder harnesses, which allowed the passengers to slide during the rollover.