NTSB Identification: LAX00FA130.
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Accident occurred Sunday, March 19, 2000 in Snelling, CA
Probable Cause Approval Date: 11/25/2003
Aircraft: Bell 212, registration: N415B
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The twin-engine helicopter impacted terrain following a mast bumping event and subsequent the loss of control. The helicopter was the second in a flight of two and trailed the lead helicopter by a short distance. The lead pilot noticed the second helicopter wreckage after the pilot did not receive a radio response from the accident pilot; he reported receiving no distress transmissions from the accident pilot. The first helicopter pilot reported they were in cruise flight between 400 - 500 feet agl at 100 knots. He said that he encountered a large bird about 1 mile before the accident. A 12-foot section of one of the main rotor blades was found early on in the wreckage debris path, which equaled approximately 1,000 feet in length and was oriented along the flight's course. Cut portions of the left skid, battery door, and the left elevator were found early on in the debris path. The separated main rotor blade underwent an overhaul approximately 8.3 hours prior to the accident. The main rotor mast displayed evidence of a mast bumping event, with indentations corresponding to the blade stops. The mast separated at the blade stop area. The commercial helicopter pilot was wearing a cast on his right leg, which extended from below his knees to his toes. The pilot received a check-out flight after not flying for 3 months. According to the pilot who provided the check-out flight, the accident pilot performed a few traffic pattern operations and was found to be able to fly. A mechanic who flew with the accident pilot during the first legs of the flight indicated the pilot was able to fly with no problems. Though there was evidence of a mast bumping event, the initiating event is unknown. Examination of the wreckage disclosed no anomalies that would have prevented normal system operation and the engines displayed evidence of rotation at the time of ground impact. The main rotor blade with the separated section was examined and it was noted that its failure was a result of overload separation and did not delaminate in flight.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

the in-flight separation of the main rotor mast while in cruise flight following a mast bumping event. The reason for the mast bumping event was not determined.

Full narrative available

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