Flight Recorders Recovered, Show RPM Drop After Noise

In its continuing investigation of the January 4, 2009, fatal accident involving a PHI Sikorsky S-76C++ helicopter that crashed in a swamp near Morgan City, LA, on Thursday the National Transportation Safety Board released the following factual information:

A detailed examination of the wreckage and components has not revealed any evidence of pre-impact engine, transmission, hydraulic servo, or systems failures. Additionally, no evidence of a midair collision, or in-flight rotorblade failure was found. An adequate amount of fuel was on board the helicopter at the time of the accident. No evidence of fuel starvation, a bird strike or electrical arcing has been found.

Data from the Penny & Giles combination flight data recorder (FDR) and cockpit voice recorder (CVR) were analyzed at the NTSB's Recorders Laboratory with download assistance from the manufacturer's facility in England, and the US Army Safety Center in Fort Rucker, AL. Both recorders captured the accident flight. 

Analysis of FDR data indicates that the helicopter was cruising at 138 knots, at an altitude of about 700 feet above the ground. The CVR indicates a loud noise followed by a substantial increase in the background noise level that was recorded on both intercom microphones and area microphone. About one second after the loud noise, the torque of both engines drops simultaneously to near zero.

The engine and rotor parameters recorded by the FDR and recorded sounds from the CVR show a simultaneous drop in RPMs over the next several seconds. The airspeed decreased slightly for the next 10 seconds while the helicopter descended. The engine continued to operate at low power levels until the end of the recorded data.

The non-volatile memory (NVM) from the engines' digital engine control units was successfully downloaded, and no faults were recorded. Additionally, NVM from the enhanced ground proximity warning system was successfully downloaded, and was consistent with DFDR data.

All three main rotor hydraulic servos and the tail rotor servo were found in good condition with no external leakage or damage. Functional tests and tear downs revealed no problems. Hydraulic reservoirs were full and no leakage was found.

The main rotor transmission had no external damage and the rotor shafts were free to rotate. The transmission case was opened and all internal components appeared normal with no damage. 

The engines were examined. They showed evidence of having been producing power at impact. No anomalies were noted that would have prevented normal operation.

Portions of the windscreen and composite center post have been recovered and sent to the NTSB laboratory in Washington, DC for further examination and analysis of the composite structure and windscreen.

Parties to the investigation include the FAA, PHI, Turbomeca, and Sikorsky.

FMI: www.ntsb.gov