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.