Bird Strike Possible Factor in PHI Helo Crash

Feb 24, 2009

A bird strike may have played a major role in causing the Jan. 4 crash of a PHI, Inc., Sikorsky S-76C++ helicopter into a marsh near Morgan City, La.

Microscopic remains of a "hawk variety" were present in a sampling of matter taken from the pilot-side windscreen, according to the NTSB in a Feb. 23 accident update.

The sampling of matter, which was tested by The Smithsonian Institution Feather Identification Lab, was taken from an area of windscreen that showed concentric ring fractures, similar to the concentric rings found in the gel coat of the fuselage just above the windscreen.

Swabs were also taken from fuselage, various inlets including the engines; rotor hub and main rotor blades. In addition, subsequent tests showed presence of small parts of feathers under a windscreen seal and in the folds of the engine inlet filter on the right side, according to the NTSB.

PHI Inc. lost satellite tracking of the aircraft (N748P) about seven minutes after it departed Amelia, La., carrying workers to oil platform in the Gulf of Mexico. The crew did not indicate there were any problems prior to the crash, in which eight of the nine people onboard were killed.

Operator PHI, Inc. had replaced the original-production laminate glass windscreen about two years prior to the accident. The company, according to the NTSB, replaces all windscreens on its S-76s, with a lighter weight, cast acrylic windscreen, which is FAA-approved under a Supplemental Type Certificate (STC).

However, about a year prior to the accident, the PHI Inc. S-76C++ windscreen was replaced a second time due to cracking.

The safety board is continuing structural analysis of the windscreen and composite center post.

Investigators also will continue examination of data from the flight recorders, issuance of the windscreen STC, as well as possible scenarios that may have caused loss of engine torque.

In a Feb. 5 accident update, the NTSB noted that data from the aircraft's combination cockpit voice/flight data recorder indicate the aircraft was cruising at 138 kt. at 700 ft. AGL (above ground level), when the CVR picked up a loud noise and a substantial increase in the background noise level. About one second later, the torque of both engines dropped simultaneously to near-zero, with corresponding drop in RPMs.

In that update, the NTSB said that tests indicated no problems with three main rotor hydraulic servos and tail rotor servo, all of which were in good condition with no external leakage or damage. Also, investigators found no leakage in hydraulic reservoirs, which were full. Also, there were no anomalies in the engines that would have prevented normal operations; evidence indicates both were producing power at time of impact.

Sikorsky S-76C photo: Sikorsky

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