Flight Details
A twin-engine helicopter was traveling to an oil platform located 90 miles south of Sabine Pass, Texas, in the Gulf of Mexico. The pilot contacted company dispatch at 0711, reporting departure from Sabine with 2.5 hours of fuel on board. At 0729, the pilot made a normal position report, stating 67 miles from destination. Another normal report at 0744 indicated 38 miles from destination. No further radio transmissions were received from the aircraft. According to the chief pilot, the helicopter's cruising altitude was most likely between 500 and 1,000 feet above ground level.
Examination Findings
Detailed examinations of the engines revealed no abnormalities. Tear-down inspection of the main transmission identified a failure of the sun gear. This failure resulted in the main rotor system not being driven. Structural deformations of the airframe indicated that the helicopter impacted the water vertically in a high rate of descent.
Probable Cause
The probable cause of the accident is the failure of the sun gear in the main transmission, which resulted in the loss of main rotor drive, leading to a vertical, high-rate descent and subsequent water impact.