NEW YORK, NY, USA
N909CP
Eurocopter MBB-BK117-B2
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.
HISTORY OF FLIGHT On April 15, 1997, at 1737 eastern daylight time, a Eurocopter BK-117-B2 helicopter, N909CP, operated by the Colgate-Palmolive Company, experienced a loss of control during the initial takeoff climb from the 60th Street heliport (6N4), New York, New York, and descended into the East River. The helicopter was destroyed. The certificated airline transport captain received serious injuries, and the co-pilot received minor injuries. One passenger was fatally injured, while the second passenger received serious injuries. Visual meteorological conditions prevailed for the corporate flight which was destined for the Westchester County Airport (HPN), White Plains, New York. The flight was operated on a VFR company flight plan and was conducted under 14 CFR Part 91. The helicopter arrived at the 60th Street heliport (6N4), from the Colgate-Palmolive Research Facility, in Piscataway, New Jersey (00NJ), a few minutes prior to the accident, and landed on the pad nearest the terminal building. Two passengers exited the helicopter, and two remained onboard. During the passenger egress, the engines remained running, and the rotors turning. The helicopter then departed on the 13th flight of the day. Witnesses observed the helicopter climb vertically from the heliport, and as the helicopter was transitioning to forward flight, a loud "pop" or "bang" was heard and the helicopter was observed to rotate in a nose right direction. Some witnesses thought they saw something depart from the tail of the helicopter while others thought that a portion of the vertical fin had bent over. Witnesses reported the helicopter rotated and descended into the East River. Some witnesses reported the air was filled with debris. The pilots exited the helicopter underwater and unaided, and were pulled from water. Divers entered the water to search for the passengers. The fuselage had rolled upside down, and divers reported they entered the cabin through the left side door. The passengers were found inside the cabin, unconscious, free of restraint, and brought to the surface. All occupants were transported to local hospitals. In an interview, the captain reported that he used maximum power for a vertical takeoff, and when the radar altimeter read 30 feet, the co-pilot called "Rotate." The captain looked outside to maintain position, and as he applied forward cyclic, he heard a loud noise and the helicopter immediately started to rotate to right. The captain said he could not feel any feedback through the rudder pedals, cyclic, or collective. He thought it was a complete tail rotor failure. He saw the co-pilot's hand near the throttles and the helicopter continued to rotate. He called for throttles off; however, the co-pilot could not reach them. The helicopter then descended into the water. The captain reported the helicopter was spinning so fast, that he had a difficult time determining up and down. He could not remember if he lowered the collective prior to impact. The captain thought the helicopter hit the water upright. He exited the helicopter underwater and headed toward the surface. In an interview, the co-pilot reported that after the passengers disembarked, he closed the main cabin door and reentered the cockpit. The takeoff was normal with the torque about 82 to 83 percent, and the helicopter was smooth. When the helicopter reached 30 feet, he called "rotate", and the captain pitched the nose forward. At that point he heard a loud bang, and the nose started to rotate to the right. As the helicopter spun around, he could see yellow and orange debris floating in the air. He braced himself with his left hand on the instrument panel, and the right hand on the number 1 throttle, awaiting a power-off call by the captain. When it didn't come, he removed his right hand. As the helicopter moved over the water, the captain called "Power off, power off"; however, the speed of the rotation had increased, and he was unable to reach the throttles. The helicopter impacted the water, and the co-pilot exited underwater while the helicopter was still descending to the bottom. The surviving passenger reported that he had no direct memory of the accident. The accident occurred during the hours of daylight at 40 degrees, 45 minutes, 36 seconds North Latitude and 73 degrees, 57 minutes, 24 seconds West Longitude. OTHER DAMAGE The upper 3 feet of the helicopter's vertical fin came to rest inside the waiting room of the heliport operations building. A window was shattered and the window frame was also damaged. Glass fragments were scattered about on the floor and there was a spill of hydraulic fluid on the carpet. PERSONNEL INFORMATION The captain held an Airline Transport Pilot certificate for rotorcraft/helicopter, and private pilot privileges for airplane single engine land. He was issued a First Class Federal Aviation Administration (FAA) Airman Medical Certificate on August 6, 1996, with the limitation to wear corrective lenses. According to the NTSB Pilot/Operator Aircraft Accident Report, he had accumulated a total of 9,400 hours, of which 3,900 were in the BK-117. He was issued a flight review by a company pilot in the BK-117, on January 4, 1996. He had attended a Helicopter Instrument Refresher course on February 26, 1997, at Flight Safety International, in Vero Beach, Florida. The training included single engine operations that were conducted in an S-76 simulator. The last documented emergency training conducted in a BK-117 occurred on October 23, 1993, with an American Eurocopter instructor pilot. The co-pilot held an Airline Transport Pilot certificate for rotorcraft/helicopter, and private pilot privileges for airplane single engine land. He was issued a First Class FAA Airman Medical Certificate on August 20, 1996, with a limitation to possess corrective lenses. According to the NTSB Pilot/Operator Aircraft Accident Report, he had accumulated a total of 10,250, of which 142 hours were in the BK-117. He last flight review occurred on November 11, 1996, in a Sikorsky S-76 simulator, at the Flight Safety International facility in Vero Beach, Florida, while in the employment of another company. The co-pilot had received individual flight and ground training from the Colgate-Palmolive chief pilot, and the other two captains in the company. The training consisted of several hours from each person on the cockpit, company procedures, and techniques used in flying the BK-117, but he had not attended the manufacturer's schools. The Chief pilot reported the co-pilot had been scheduled for formal training; however, the accident occurred prior to the scheduled date of training. The investigation revealed that a BK-117 simulator did not exist. The S-76 simulator was used for helicopter general and instrument procedures. Emergency procedures specific to the BK-117 were not practiced in the S-76 simulator. AIRCRAFT INFORMATION The helicopter was a 1989 Eurocopter BK-117-B2, delivered new to the operator on December 22, 1989, as a B1 model, and later upgraded to a B2. The helicopter was maintained under the manufacturer's inspection program, utilizing a Progressive Maintenance Program with phased inspections, which occurred at 50 hour intervals. The helicopter was certificated for single pilot operations; however, the company procedure was to use a co-pilot on all passenger flights. The passenger cabin was fitted with facing couch seats, which seated three passengers each, forward and aft. Pull out drawers under the couch seats contained personal flotation devices (life vests) for the passengers. There were four doors on the helicopter. Two of the doors were the pilot's entrance doors, and two doors were for the main cabin. The primary cabin door was an airstair door located on the left side of the fuselage. It was hinged at the bottom, and was used for normal passenger entry and exit. The emergency exit door was a sliding door, located on the right side of the helicopter. The sliding door opened from forward to aft. The forward couch obscured the normal door release handle inside the cabin. In addition, an emergency actuation handle was located on the upper left corner of the emergency door as viewed from inside the cabin. When the handle was pulled, the door was released from the helicopter to fall away. A white placard with red lettering was located next to the inside emergency exit door release. AERODROME INFORMATION The 60th Street heliport was owned by the City of New York, and managed by Johnson Controls. The heliport was 330 feet wide and 75 feet deep. It was bordered on three sides by obstructions, and on the fourth side, by the East River. WRECKAGE AND IMPACT INFORMATION The helicopter was removed from the East River on the night of April 15, 1997. It was examined at the accident site, with follow-up examinations conducted at the Colgate-Palmolive facility at Teterboro, New Jersey. Divers reported that the fuselage was nose down, with the tail boom resting against the seawall. The fuselage had rotated to the inverted position. When raised from the water, the tail boom had separated from the fuselage and was held by hydraulic and electrical lines. The tail rotor drive shaft was bent about 40 degrees to the right where it exits the aft fuselage. There was an additional bend in the opposite direction, just aft of the horizontal stabilizer. At that bend, there was an impact mark on the exterior surface of the tail boom. Impact damage was visible on the left side of the fuselage. Plexiglas was fractured, and the skin on the left side of the fuselage was crushed inboard about 3 inches between the rivet lines. The damage was consistent with a water impact on the left side. The left side airstair door was partially separated from the fuselage. The divers reported that they had opened the door underwater. Flight control continuity was verified to the rudder pedals, and to the cyclic in both lateral and fore/aft movements. The collective was jammed in the up position. Control linkages to the collective were verified as connected. Both engine compressor sections were rotated. The turbine sections rotated freely in the freewheeling direction, and would not move in the power direction. There was no evidence of foreign object damage (FOD) in the intakes or exhausts. The chip plugs on both engines were clean. The engine power controls were in the flight position. The input shaft to the transmission could be rotated in the freewheeling direction, but not in the power direction. The pitch link control rods to the main rotor blades were bent and fractured. The red main rotor blade was fractured about 12 inches from the hub blade grip. The remaining main rotor blades were fractured within 1-2 inches of the hub. Impact marks were found on the seawall above the East River. The marks matched the color of the main rotor blades. Other than small pieces of skin and interior foam, the main rotor blades were not recovered. The spars of the tail rotor blades remained attached to the blade grips. The tail rotor and 90 degree gearbox was still attached to the upper portion of the vertical fin. Both tail rotor blades were damaged, with more damage on the trailing edge portion of the blades. The left horizontal stabilizer with its attached vertical stabilizer was found near the ramp side entrance to the waiting room. The ramp was littered with small pieces of white and orange fiberglass, and orange foam. The tail rotor blades were painted white with orange tips, and the interior foam for the tail rotor blades and main rotor blades was orange. MEDICAL AND PATHOLOGICAL INFORMATION Blood samples were released by both pilots voluntarily, and were forwarded to the FAA Toxicology Accident Research Laboratory in Oklahoma City, Oklahoma. No evidence of drugs or alcohol was found. An autopsy was conducted on the deceased passenger on April 16, 1997, by Dianne Kaluk, MD, Medical Examiner, City of New York, New York. SURVIVAL ASPECTS The Chief Pilot for Colgate-Palmolive reported that he did not keep evacuation cards in the cabin because if a modification was made to the cabin, the information on the card would be outdated, and that would give the passengers wrong information. Emergency lights were in place over both the main cabin door (airstair), and the alternate cabin exit/emergency exit. The battery was depleted, and the system had been exposed to salt water. The system could not be tested. A passenger who was on the flight into the 60th street heliport was interviewed. She reported that she had flown in company helicopters about 2 to 3 times a week for the last 3 1/2 years, and was only aware of the main cabin door, which they entered and exited through. She was aware of the location of the personal flotation equipment; however, she had never tried on a life preserver. Interviews were conducted with six persons who had flown in company helicopters ranging from between 4 months, to 15 years. The interviews disclosed three of the passengers were not certain if there was another exit in the cabin, its location, or its operation, other than the airstair door that they normally entered and exited through. Two of the passengers thought the seat cushions were personal flotation devices for the occupants. No one had tried on the personal flotation equipment. The passengers also commented that passenger briefings were not given on every flight, but were given to new passengers prior to their first flight on the helicopter. The investigation revealed that passenger briefings included, remaining seated and to wait for a crewmember to open or close the main cabin door, the use of air vents, the telephone, the location of emergency flotation equipment, and the location of the emergency exit. The co-pilot would normally perform the briefing. The lift vests were contained in sealed packets, which if opened rendered them unusable. No spare life vests were available for demonstration or to try on. TESTS AND RESEARCH The right side passenger door/emergency exit was recovered from the river. The door had been actuated utilizing the external handle. The inside release was still in the stowed position. The emergency door was placed on the helicopter and latched in place. The door was actuated open and closed several times, and then jettisoned utilizing the inside cabin release with no problems noted. A check with the divers failed to reveal who had opened the right side passenger door/emergency exit. The separated portion of the vertical fin, and the lower portion of the vertical fin were forward to the NTSB Metallurgical Laboratory in Washington, DC for further examination. Fatigue cracks were observed in the vertical fin skin, frame assembly, stiffener rib, and spar. Compression and deformation were found on the right side of the fin. The skin crack on the left side of the vertical fin measured 5.5 inches long. About 1 inch was visible, with the rest of the crack located under the yaw SAS mounting support. Five distinct cracks with independent initiations near blind rivet holes were found. For two segments, the origins were under the heads of blind rivets. The left hand frame assembly was fractured about 0.5 inches below the plane of the skin fracture. The fracture face had a polished appearance, and further examination did not uncover the original fracture features. The L shaped stiffener rib was fractured about 0.5 inches above the level of the skin break through a blind rivet hole in one leg and a lighting hole in the other leg. The fatigue initiated at multiple origins on the outboard face of the rib, progressed through the thickness and away from the hole, in the forward and aft directions. About half of the rib was fractured in fatigue, with the remainder in tensile overstress. Two separate cracks were found in the spar, one in the spar cap, and the other in the spar web. The fracture face of the spar cap crack, which intersected a blind rivet hole, was polished and the original features were obliterated. The spar web crack was a fatigue crac
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.
Source: NTSB Aviation Accident Database
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