NTSB Identification: NYC97FA076.
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Accident occurred Tuesday, April 15, 1997 in NEW YORK, NY
Probable Cause Approval Date: 05/16/2000
Aircraft: Eurocopter MBB-BK117-B2, registration: N909CP
Injuries: 1 Fatal,2 Serious,1 Minor.
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.
After taking off, the helicopter climbed to approximately 30 feet, and produced a loud bang. The helicopter rotated nose right several times, descended, struck the heliport pier and continued into the East River where it submerged. The pilots were evacuated underwater; the passengers were found in the cabin unconscious and recovered by divers. The throttles were found in the flight position. The investigation revealed that the upper 3 feet of the vertical fin had failed due to fatigue fractures and had separated, along with the tail rotor assembly. About 4 1/2 years prior, the left-hand yaw SAS actuator mounting plate attached to the vertical fin developed a crack and was replaced using blind rivets in lieu of the solid rivets specified in the manufacturer's design drawings. Neither the repair nor the substitution of rivets was addressed in the manufacturer's maintenance manual. Literature from the rivet manufacturer indicated that blind rivets may be substituted for solid rivets in most applications. No specific reference by the FAA was found to allow for this rivet substitution. The investigation revealed 11 other helicopters with fatigue cracking in the vertical fin spar similar to the accident helicopter. Testing revealed that materials fastened with blind rivets are more susceptible to fatigue cracking than materials fastened with solid rivets. Passenger interviews disclosed that many were not aware of emergency exit locations, or how to operate them; life vests were available, but were not used.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Fatigue failure of the vertical fin, accelerated by the installation of blind rivets in lieu of solid rivets in the replacement of the yaw SAS mount support, which resulted in the loss of helicopter directional control and collision with the terrain (water). Factors contributing to the accident were: a lack of information regarding repair of the yaw SAS mount support in the manufacturer's maintenance manuals, and the design of the vertical fin which was susceptible to fatigue cracking. An additional factor was the lack of an adequate passenger briefing. Full narrative available
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