# NTSB NYC97FA076: Eurocopter MBB-BK117-B2, N909CP, New York, NY, April 15, 1997 - Type: NTSB accident investigation - Classification: Accident · Fatal · Field investigation · Final report - Date: April 15, 1997, 17:37 local (21:37 UTC) - Place: New York, NY - Coordinates: 40.759021, -73.969497 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=40.7590&lon=-73.9695&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Highest injury: Fatal - Injuries: 1 fatal, 2 serious, 1 minor - Status: Completed, report May 16, 2000 - Report: Approved by Office Director - Safety recommendations: Yes - NTSB case key (mKey): 39272 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=NYC97FA076 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/39272/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=39272 - Page: https://openairdocs.org/ntsb/NYC97FA076 ## 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. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, takeoff - initial climb - nacelle/pylon,plate - maintenance,replacement, company maintenance personnel (cause) - information - inadequate, manufacturer (contributing factor) - acft/equip,inadequate design, manufacturer (contributing factor) - misc rotorcraft,tail pylon - fatigue (cause) - misc rotorcraft,tail pylon - separation (cause) - Loss of control - in flight, takeoff - initial climb - In flight collision with terrain/water, descent - emergency - terrain condition - water - passenger briefing - inadequate, pilot in command (contributing factor) ## Analysis 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. ## Factual narrative 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 n ## Aircraft - Registration: [N909CP](https://openairdocs.org/deregistered/N909CP-1997-08-29), registration cancelled 1997-08-29, S/N 7189 (OpenAirDocs) - Reported make and model: Eurocopter MBB-BK117-B2 (MBB-BK117-) - Registry model: [Messerschmitt-Bolkow-Blohm BK 117 B-2](https://openairdocs.org/model/messerschmitt-bolkow-blohm-bk-117-b-2) (registry code 5626013) (OpenAirDocs) - Category: Helicopter - Serial number: 7189 - Airframe hours: 4190 - Engines: Lycoming LTS101-750B-1 650 horsepower turbo shaft - Damage: Destroyed - Flight: Executive/Corporate, Part 91 - Registered owner: Colgate Palmolive Company - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, March 25, 1997, 36 hours before - Departed: 6N4 - Destination: HPN, WHITE PLAINS, NY - Flight plan: Company VFR - Airport: 6N4, 60th Street Heliport ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 52; private, airline transport; airplane ratings: single-engine land; instrument ratings: helicopter; medical: class 1, valid medical--w/ waivers/lim; seat: right; toxicology performed; flight hours: 9,400 total, 3,900 in this make and model, 5,050 as pilot in command, 154 in the last 90 days, 53 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 200° at 12 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 55 °F, dew point 37 °F - Altimeter: 30.00 inHg - Observed at: LGA, 4 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19970415005959A](https://openairdocs.org/incident/19970415005959A), Apr 15, 1997: Bolkms BK117B1, New York, NY, Destroyed, 1 fatal. (.4)After climbing about 30' after takeoff, loud bang was heard, then helicopter (hel) rotated right, descended, struck edge of heliport, and descend into east… ## Docket (47 files) The files NTSB released with the investigation on March 18, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=39272. 19.7 MB in all. - Supplement c (item 1, PDF, 4 pages, 408 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404772&FileExtension=pdf&FileName=Supplement%20C-Master-Rel.pdf - Supplement d (item 2, PDF, 6 pages, 503 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404783&FileExtension=pdf&FileName=Supplement%20D-Master-Rel.pdf - Supplement e (item 3, PDF, 2 pages, 145 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405022&FileExtension=pdf&FileName=Supplement%20E-Master-Rel.pdf - Supplement g (item 4, PDF, 1 page, 102 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404673&FileExtension=pdf&FileName=Supplement%20G-Master-Rel.pdf - Supplement s (item 5, PDF, 1 page, 74 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405126&FileExtension=pdf&FileName=Supplement%20S-Master-Rel.pdf - Pilot-operator aircraft accident report NTSB form 61201-2 (item 6, PDF, 6 pages, 443 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404328&FileExtension=pdf&FileName=Pilot-Operator%20Aircraft%20Accident%20Report%20NTSB%20Form%2061201-2-Master-Rel.pdf - NTSB summaries of interviews (item 7, PDF, 20 pages, 324 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405187&FileExtension=pdf&FileName=NTSB%20Summaries%20of%20Interviews-Master-Rel.pdf - Witness statement (item 8, PDF, 2 pages, 67 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405129&FileExtension=pdf&FileName=Witness%20Statement-Master-Rel.pdf - NTSB metallurgist's factual report (item 9, PDF, 18 pages, 673 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405658&FileExtension=pdf&FileName=NTSB%20Metallurgist%27s%20Factual%20Report-Master-Rel.pdf - Cp work order for yaw sas mounting support replacement (item 10, PDF, 3 pages, 155 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404710&FileExtension=pdf&FileName=CP%20Work%20Order%20for%20Yaw%20SAS%20Mounting%20Support%20Replacement-Master-Rel.pdf - Last 1200 hour inspection (item 11, PDF, 12 pages, 585 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405191&FileExtension=pdf&FileName=Last%201200%20hour%20inspection-Master-Rel.pdf - List of helicopters with cracked vertical fins (item 12, PDF, 1 page, 54 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405662&FileExtension=pdf&FileName=List%20of%20Helicopters%20with%20cracked%20vertical%20fins-Master-Rel.pdf - Eurocopter report on rivet lifetime (item 13, PDF, 11 pages, 960 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405666&FileExtension=pdf&FileName=Eurocopter%20Report%20on%20Rivet%20Lifetime-Master-Rel.pdf - Cherry Textron report of rivet lifetime (item 14, PDF, 24 pages, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405228&FileExtension=pdf&FileName=Cherry%20Textron%20Report%20of%20Rivet%20Lifetime-Master-Rel.pdf - FAA letter (item 15, PDF, 2 pages, 79 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405033&FileExtension=pdf&FileName=FAA%20Letter-Master-Rel.pdf - Release of aircraft wreckage NTSB form 612015 (item 16, PDF, 2 pages, 94 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404920&FileExtension=pdf&FileName=Release%20of%20Aircraft%20Wreckage%20%20NTSB%20Form%20612015-Master-Rel.pdf - Statement of party representatives to NTSB investigation (item 17, PDF, 4 pages, 362 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405954&FileExtension=pdf&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master-Rel.pdf - Photo-1 helicopter recovery from east river (item 18, PDF, 1 page, 15 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405416&FileExtension=pdf&FileName=Photo-1%20Helicopter%20recovery%20from%20East%20River-Master-Rel.pdf - Photo-2 top of vertical pylon and tail rotor found inside waiting room (item 19, PDF, 1 page, 23 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404925&FileExtension=pdf&FileName=Photo-2%20Top%20of%20vertical%20pylon%20and%20tail%20rotor%20found%20inside%20waiting%20room-Master-Rel.pdf - Photo-3 60th street heliport arrow points to location where helicopter went into water (item 20, PDF, 1 page, 14 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1581976&FileExtension=pdf&FileName=Photo-3%2060th%20Street%20Heliport%20%20Arrow%20points%20to%20location%20where%20helicopter%20went%20into%20water-Master.pdf - Exhibit c photo-1 (item 21, PDF, 1 page, 13 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404929&FileExtension=pdf&FileName=Exhibit%20C%20Photo-1-Master-Rel.pdf - Exhibit c photo-2 (item 22, PDF, 1 page, 14 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405741&FileExtension=pdf&FileName=Exhibit%20C%20Photo-2-Master-Rel.pdf - Exhibit c photo-3 (item 23, PDF, 1 page, 15 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405576&FileExtension=pdf&FileName=Exhibit%20C%20Photo-3-Master-Rel.pdf - Email from colgate-palmolive (item 24, PDF, 1 page, 49 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13404933&FileExtension=pdf&FileName=Email%20from%20Colgate-Palmolive-Master-Rel.pdf - Email to FAA (item 25, PDF, 1 page, 56 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13406034&FileExtension=pdf&FileName=Email%20to%20FAA-Master-Rel.pdf - Drawing from colgate-palmolive showing location of crack (item 26, PDF, 1 page, 57 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405496&FileExtension=pdf&FileName=Drawing%20from%20Colgate-Palmolive%20showing%20location%20of%20crack-Master-Rel.pdf - Copy of FAA form 337 for tail boom reskinning (item 27, PDF, 2 pages, 233 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405501&FileExtension=pdf&FileName=Copy%20of%20FAA%20Form%20337%20for%20tail%20boom%20reskinning-Master-Rel.pdf - Submission from colgate-palmolive letter (item 28, PDF, 7 pages, 89 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1582004&FileExtension=pdf&FileName=Submission%20from%20Colgate-Palmolive%20letter-Master.pdf - Exhibit a (item 29, PDF, 20 pages, 996 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405504&FileExtension=pdf&FileName=Exhibit%20A-Master-Rel.pdf - Exhibit b (item 30, PDF, 5 pages, 529 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13406119&FileExtension=pdf&FileName=Exhibit%20B-Master-Rel.pdf - Exhibit d (item 31, PDF, 1 page, 108 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13406122&FileExtension=pdf&FileName=Exhibit%20D-Master-Rel.pdf - Eurocopter alert service bulletin-REV-1 (item 32, PDF, 4 pages, 236 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13406971&FileExtension=pdf&FileName=Eurocopter%20Alert%20Service%20Bulletin-Rev-1-Master-Rel.pdf - Eurocopter alert service bulletin-REV-2 (item 33, PDF, 3 pages, 195 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1582020&FileExtension=pdf&FileName=Eurocopter%20Alert%20Service%20Bulletin-Rev-2-Master.pdf - Eurocopter alert service bulletin-REV-3 (item 34, PDF, 20 pages, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1582022&FileExtension=pdf&FileName=Eurocopter%20Alert%20Service%20Bulletin-Rev-3-Master.pdf - Eurocopter alert service bulletin-REV-4 (item 35, PDF, 20 pages, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1582024&FileExtension=pdf&FileName=Eurocopter%20Alert%20Service%20Bulletin-Rev-4-Master.pdf - FAA priority letter AD 97-09-16 (item 36, PDF, 3 pages, 77 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13406160&FileExtension=pdf&FileName=FAA%20Priority%20Letter%20%20%20%20%20AD%2097-09-16-Master-Rel.pdf - FAA airworthiness directives AD 97-20-16 (item 37, PDF, 5 pages, 162 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13406166&FileExtension=pdf&FileName=FAA%20Airworthiness%20Directives%20%20%20%20%20%20AD%2097-20-16-Master-Rel.pdf - Submittal-2-colgate-palmolive company (item 38, PDF, 8 pages, 593 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13407156&FileExtension=pdf&FileName=Submittal-2-Colgate-Palmolive%20Company-Master-Rel.pdf - Lap joint fatigue comparison report-textron aerospace fasteners (item 39, PDF, 77 pages, 4.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13407315&FileExtension=pdf&FileName=Lap%20Joint%20Fatigue%20Comparison%20Report-Textron%20Aerospace%20Fasteners-Master-Rel.pdf - FAA response of questions about approval of repair on vertical fin (item 40, PDF, 2 pages, 79 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13406829&FileExtension=pdf&FileName=FAA%20Response%20of%20Questions%20About%20Approval%20of%20Repair%20on%20Vertical%20Fin-Master-Rel.pdf - NTSB letter requesting additional information from American Eurocopter (item 41, PDF, 1 page, 50 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13407237&FileExtension=pdf&FileName=NTSB%20Letter%20Requesting%20Additional%20Information%20From%20American%20Eurocopter-Master-Rel.pdf - Response from Eurocopter to NTSB request for additional information (item 42, PDF, 21 pages, 655 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13405866&FileExtension=pdf&FileName=Response%20from%20Eurocopter%20to%20NTSB%20Request%20for%20Additional%20Information-Master-Rel.pdf - Old and new process manuals for cherrylock and cherrymax rivets (item 43, PDF, 4 pages, 450 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13407889&FileExtension=pdf&FileName=Old%20and%20New%20Process%20Manuals%20for%20CherryLock%20and%20CherryMax%20Rivets-Master-Rel.pdf - Record of BK-117S with cracks in vertical fin (item 44, PDF, 1 page, 20 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13408120&FileExtension=pdf&FileName=Record%20of%20BK-117s%20with%20Cracks%20in%20Vertical%20Fin-Master-Rel.pdf - Fax from American Eurocopter about repairs to BK-117S s-n 7201-7207 (item 45, PDF, 16 pages, 520 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13408042&FileExtension=pdf&FileName=FAX%20from%20American%20Eurocopter%20about%20repairs%20to%20BK-117s%20S-N%207201-7207-Master-Rel.pdf - Fax from American Eurocopter about repairs to vertical fin of 2 BK-117S (item 46, PDF, 8 pages, 342 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13407242&FileExtension=pdf&FileName=FAX%20from%20American%20Eurocopter%20about%20repairs%20to%20vertical%20fin%20of%202%20BK-117s-Master-Rel.pdf - Addendum-4-factual report (item 47, PDF, 8 pages, 130 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13407892&FileExtension=pdf&FileName=Addendum-4-Factual%20Report-Master-Rel.pdf From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.