NTSB Identification: LAX02LA213.
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Accident occurred Tuesday, July 02, 2002 in Chatsworth, CA
Probable Cause Approval Date: 06/30/2004
Aircraft: Robinson R22 BETA, registration: N4072T
Injuries: 1 Serious,1 Minor.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The 2,155-hour pilot reported that the helicopter developed an abnormal vibration while en-route to a local practice area. The pilot added that he became concerned about the unusual vibration and elected to land the helicopter as soon as possible to investigate the source of the vibration. The pilot executed a power-on approach to a terraced paved area located to the right of his intended course. While on the approach on a northerly heading, as the pilot was flaring the helicopter for a landing, control was lost after the main rotor blades came in contact with the terraced terrain to his right-front. The pilot stated that the engine was performing "normally" and he did not experience a loss of engine power. He added that at the time of the accident, the winds at the accident site were from the south at an estimated 10 to 13 knots. On June 25, 2002, the Robinson Helicopter Company issued an R22 Safety Alert Letter dealing with unusual vibrations and the possibility of a main rotor blade crack. The letter states that "IF MAIN ROTOR VIBRATION INCREASES RAPIDLY OR BECOMES SEVERE DURING FLIGHT, LAND IMMEDIATELY." The pilot recalled receiving this letter three days prior to the accident and indicated this as the reason for his landing attempt. Both tail rotor blades were broken off about 3 ½ inches from their outboard mount points with severe leading edge damage to both blades. One main rotor blade was bent aft and up from its normal position leaving the trailing edge buckled. The other main rotor blade was bent aft and down from its normal position leaving the trailing edge buckled. Small cracks were observed on both main rotor blades near the root fitting and spar cover area. Due to the observed cracks in the main rotor blade root area, the sealant was removed from both blades and they were subjected to a dye penetrate inspection per Robinson Helicopter Company Service Letter 21A. No indications of cracks in the root fitting material of both blades were found.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's inadequate flare resulting in rotor blade contact with the ground. Contributing factors were the high altitude and the airframe vibration for an undetermined reason. Full narrative available
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