Accident MBB BK 117B-2 N909CP,
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ASN Wikibase Occurrence # 37037
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Date:Tuesday 15 April 1997
Time:17:37 LT
Type:Silhouette image of generic BK17 model; specific model in this crash may look slightly different    
MBB BK 117B-2
Owner/operator:Colgate Palmolive Company
Registration: N909CP
MSN: 7189
Year of manufacture:1989
Total airframe hrs:4190 hours
Engine model:Lycoming LTS101-750B-1
Fatalities:Fatalities: 1 / Occupants: 4
Aircraft damage: Destroyed
Location:New York, NY -   United States of America
Phase: Initial climb
Departure airport:(6N4)
Destination airport:White Plains, NY (HPN
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
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.

Probable Cause: 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.

Accident investigation:
Investigating agency: NTSB
Report number: NYC97FA076
Status: Investigation completed
Duration: 3 years 1 month
Download report: Final report




Revision history:

24-Oct-2008 10:30 ASN archive Added
24-Jul-2010 12:37 Alpine Flight Updated [Aircraft type, Other fatalities, Source]
20-Aug-2010 03:07 TB Updated [Aircraft type]
20-Nov-2012 11:56 TB Updated [Time, Operator, Source, Narrative]
21-Dec-2016 19:23 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
08-Apr-2024 15:57 ASN Update Bot Updated [Time, Operator, Other fatalities, Phase, Destination airport, Source, Narrative, Category, Accident report]

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