What happened
On the flight, a pilot with 2,155 hours of experience reported that the Robinson R22 developed an abnormal vibration while en-route to a local practice area. Concerned by the unusual vibration, the pilot elected to land the helicopter as soon as possible to investigate the source. The pilot executed a power-on approach toward a terraced paved area located to the right of the intended course.
While on a northerly heading during the flare for landing, control was lost after the main rotor blades made contact with the terraced terrain to the right-front of the aircraft. The pilot reported that the engine was performing normally and there was no loss of engine power at the time of the accident. Weather conditions at the site involved winds from the south at approximately 10 to 13 knots.
The investigation
The investigation examined the damage to the rotor system. Both tail rotor blades were broken off approximately 3.5 inches from their outboard mount points, exhibiting severe leading edge damage. Regarding the main rotor, one blade was bent aft and up from its normal position with a buckled trailing edge, while the other blade was bent aft and down with a buckled trailing edge.
Small cracks were observed on both main rotor blades near the root fitting and spar cover area. Following the discovery of these cracks, the sealant was removed from both blades to allow for a dye penetrant inspection in accordance with Robinson Helicopter Company Service Letter 21A. This inspection found no indications of cracks in the root fitting material of either blade.
Findings
- The pilot had received an R22 Safety Alert Letter from the Robinson Helicopter Company on June 25, 2002, which addressed unusual vibrations and the potential for main rotor blade cracks.
- This letter instructed pilots to land immediately if main rotor vibration increases rapidly or becomes severe.
- The pilot recalled receiving this specific safety alert three days prior to the accident and cited it as the reason for attempting the landing.