# NTSB LAX98LA200: Hughes 369HS, N95MS, Pacific Ocean (Pacific Ocean), June 16, 1998 - Type: NTSB accident investigation - Classification: Accident · Fatal · Limited investigation · Final report - Date: June 16, 1998 - Place: Pacific Ocean (Pacific Ocean) - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Highest injury: Fatal - Injuries: 2 fatal - Status: Completed, report April 20, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 30122 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX98LA200 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/30122/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=30122 - Page: https://openairdocs.org/ntsb/LAX98LA200 ## Probable cause The improper shimmying of the tail rotor driveshaft by maintenance personnel which induced fatigue in the tail rotor driveshaft coupling causing it to fail, which resulted in a loss of tail rotor control. A factor is the failure of the pilot to recognize the warning vibrations indicating impending failure of the coupling. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of control - in flight, takeoff - initial climb - rotor drive system,tail rotor drive shaft - overtorque - maintenance,adjustment - improper, other maintenance personnel (cause) - rotor drive system,tail rotor drive shaft coupling - fatigue - rotor drive system,tail rotor drive shaft coupling - failure - unsafe/hazardous condition warning - not understood, pilot in command (contributing factor) - In flight collision with terrain/water, descent - uncontrolled - tail rotor/anti-torque control - not possible, pilot in command ## Analysis Witnesses reported that the helicopter took off from the ship, and about 85 agl, it started spinning to the right. The pilot called 'No control, MAYDAY,' on the radio. The helicopter nosed down and impacted the water. The aircraft was recovered, except for the aft portion of the tail rotor driveshaft and tailboom, including the tail rotor gearbox and all tail rotor system rotating components. The wreckage was shipped to the United States for examination. The aircraft had undergone a major overhaul/rebuild and annual inspection following a previous accident on March 11, 1997. After completing 1.4 hours of test flights, the helicopter was then partially disassembled and transported to California, and subsequently shipped to American Samoa. Maintenance personnel in Hawaii reassembled the aircraft, after replacing several parts. The owner of the maintenance facility stated some of the life-limited components were replaced with parts with less accrued total time. He reported that they had to adjust the shim on the tail rotor driveshaft because it was 'way off, too tight.' No test run was performed after reassembly. Examination of the helicopter following recovery revealed the forward tail rotor driveshaft coupling evidenced a fracture and separation. The forward portion of the coupling remained attached at the main transmission output pinion, while the aft portion of the coupling remained attached to the forward end of the tail rotor driveshaft. The coupling bolts evidenced smearing of the bolt heads. Scanning electron microscopy revealed a total of eight fracture surfaces. Six fracture surfaces displayed features consistent with fatigue, although much of the mechanical damage prevented identification of origin locations, and the other two fracture surfaces exhibited features consistent with overstress separation. Further, the coupling is designed with a built-in fail-safe feature that will continue to provide torque transmission in the event that a flex frame leg or bolt fractured. When the fail-safe engages, the unbalance of the coupling increases with a resultant increase in the vibration, alerting the pilot to take the appropriate action and land. ## Factual narrative HISTORY OF FLIGHT On June 16, 1998, at 1400 hours local time, a Hughes 369HS, N95MS, collided with the Pacific Ocean approximately 1,000 miles north-northwest of American Samoa following a takeoff from a fishing vessel. The helicopter, operated by the Caribbean Fishing Company, Pittsburgh, Pennsylvania, was destroyed. The pilot commercial pilot suffered fatal injuries. The passenger/observer, who was also the captain of the ship, was not found and is presumed to have suffered fatal injuries. The flight was conducted under the provisions of 14 CFR Part 91 as a tuna spotting operation. Visual meteorological conditions prevailed and no flight plan was filed. There were 15 crewmembers aboard the vessel when the helicopter crash occurred, 7 of who witnessed the accident and were subsequently interviewed. Copies of their interviews are attached to this file. They reported that it was the first flight of the day for the tuna spotting operation. The witnesses stated that the helicopter took off and reached the altitude of the ship's mast, about 85 feet agl. They reported that the aircraft began "spinning around." One witness heard the pilot call on the radio, "No control, MAYDAY." The helicopter nosed down and impacted the water. At that point, the ship was stopped and speedboats were dropped into the water. The pilot/mechanic was rescued and died about 15 minutes after being brought onboard the fishing vessel. The United States Coast Guard continued to search for the missing captain, utilizing five ships and two helicopters. The search was suspended on Friday, June 19, 1998. The helicopter was recovered, except for the aft portion (approximately the last 3 feet) of the tail rotor driveshaft and tail boom, including the tail rotor gearbox and all tail rotor system rotating components. The wreckage was shipped to the United States for examination. PERSONNEL INFORMATION According to the Federal Aviation Administration (FAA) airman records, the pilot held a commercial pilot certificate with an airplane multiengine land and instrument airplane rating. He also had private privileges for airplane single engine land and rotorcraft-helicopter. According to the pilot's employment application, dated May 1998, he indicated that he had 1,120 total hours of flight time, including 626 total hours in helicopters and 260 hours in a Hughes 369HS. He also listed 191 hours of fish spotting. The application indicated that the pilot's last biennial flight review was in May 1997. The pilot held a first-class medical certificate dated September 26, 1996. The pilot also performed duties aboard the ship as the helicopter mechanic. The FAA records showed that he held an FAA mechanic's certificate, with both airframe and powerplant ratings, issued on March 17, 1997. AIRCRAFT INFORMATION The aircraft had undergone a major overhaul/rebuild and annual inspection following an accident in which a pilot experienced a loss of power and made a forced landing in the water on March 11, 1997. The rebuild/overhaul was completed with an airframe time-since-new of 5,988.9 hours. After completing 1.4 hours of maintenance test flights, the helicopter was then partially disassembled and transported to California, and subsequently shipped to American Samoa. After arrival in American Samoa, maintenance personnel contracted from a facility in Hawaii reassembled the aircraft. The chief mechanic reported that preliminary external inspection of the aircraft revealed no discrepancies; however, he stated that he had to adjust the shim thickness of the driveshaft because it was "way off, too tight." Some of the life-limited components, including the main rotor blades and tail rotor blades, were replaced with parts with less accrued total time. The tail boom was also replaced. The aircraft was returned to service on May 18, 1998, with three open discrepancies indicated by the maintenance personnel: track and balance; replace engine TOT harness and calibrate; replace torque line from firewall to gauge. One of the mechanics reported that the discrepancies were left open because parts were not readily available and the ship was scheduled to leave the harbor. No test run was performed. A copy of the maintenance report is appended to this file. At the time of the accident, the helicopter had accrued a total of 29.4 hours since the overhaul/rebuild, including the 1.4 hours of maintenance test flights. WRECKAGE AND IMPACT According to witnesses, the aircraft impacted the water in a right spin, then rolled onto its left side. The left landing gear, including the permanently inflated utility floats, separated from the fuselage. The left struts forward and aft of the landing gear lower attaching flanges exhibited damage. The cockpit windscreen Plexiglas panels were blown out. DAMAGE TO AIRCRAFT The aircraft was configured for left seat command and was not equipped with dual flight controls. The collective control system was intact from the left seat collective control stick up to the lower main rotor system flight controls, and continuity was established for that portion of the system. The cyclic was intact from the left seat cyclic control stick up to the main rotor system lower flight controls. Continuity was established for that portion of the controls. The antitorque control system was intact from the left seat pedals to a fracture of the floor-routed control rod forward of the bungee spring attach fitting/aft rod end bearing. According to the maintenance manual, the directional control bungee spring installed in the accident aircraft was designed for use in the 369D series aircraft. The main rotor blades evidenced lead/lag excursions and high flapping angles. All strap pack laminates exhibited fracture damage and one main rotor blade separated completely from the main rotor system and was not recovered. A second main rotor blade was separated at the strap pack and partially wrapped around the main rotor mast and upper flight controls. The pilot and front seat passenger lap belts were intact and evidenced no damage to the webbing or the fuselage attach points. The pilot (left seat) shoulder harness was fully extended from the inertia reel, which was locked. The passenger (right seat) shoulder harness was extended approximately 2 inches and twisted 180 degrees inside the inertia reel, which was locked. The engine remained intact and evidenced external damage consistent with the effects of saltwater corrosion. A fuel system inspection and vacuum check was not conducted due to the saltwater submersion and corrosion of fuel system components, including the fuel cell. The tail rotor driveshaft exhibited no rotational damage. The tail rotor driveshaft forward coupling, manufactured by Kamatics Corporation, evidenced a fracture and separation. The forward portion of the coupling remained attached at the main transmission output pinion, while the aft portion of the coupling remained attached to the forward end of the tail rotor driveshaft. The coupling bolts evidenced smearing of the bolt heads. Each fractured coupling section exhibited compression bending of the flanges. The coupling was sent to the Safety Board Materials Laboratory for further analysis. A copy of the metallurgy report is appended to this file. TESTS AND RESEARCH One piece of the coupling was attached to the rotor brake disc, while the other piece, from the drive shaft side, was not attached to any neighboring hardware. Two sections of flex coupling were bolted to each piece of the gearshaft coupling and both contained two fractures. Examination revealed that the fractures from the two pieces of driveshaft coupling did not match, indicating that one or more pieces were missing from the coupling. The coupling flanges were bent on both sides. The forward coupling flange was bent forward, toward the disc, and the aft coupling ## Aircraft - Registration: [N95MS](https://openairdocs.org/deregistered/N95MS-2018-01-24), registration cancelled 2018-01-24, S/N 1130536S (OpenAirDocs) - Reported make and model: Hughes 369HS - Registry model: [Hughes 369HS](https://openairdocs.org/model/hughes-369hs) (registry code 4470728) (OpenAirDocs) - Registry engine: [Allison 250-C20 series](https://openairdocs.org/engine/allison-250-c20-series) (registry code 03020, turbo-prop) (OpenAirDocs) - Category: Helicopter - Serial number: 1130536S - Airframe hours: 6018 - Engines: Allison 250-C20B 415 horsepower turbo shaft - Damage: Destroyed - Flight: Aerial observation, Part 91 - Registered owner: Caribbean Fishing Company - Airworthiness certificate: Standard, Normal - Last inspection: Annual, May 18, 1998, 29 hours before ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 30; commercial, private; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 1,120 total, 260 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 90° at 5 knots - Visibility: 12 statute miles - Lowest ceiling: none - Temperature: 84 °F ## 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 19980616013669A](https://openairdocs.org/incident/19980616013669A), Jun 16, 1998: Hughes 369HS, Pacific Ocean, American Samoa, Destroyed, 2 fatal. (.4) Witnesses reported that the helicopter took off from the ship, and about 85 AGL, it started spinning to the right. The pilot called 'no control, mayday,'… ## Other investigations on N95MS (1) 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. - [NTSB LAX97LA120](https://openairdocs.org/ntsb/LAX97LA120), Mar 11, 1997: McDonnell Douglas MD 369HS (N95MS), Pacific Ocean (Pacific Ocean), destroyed. Probable cause: A loss of engine power due to a deteriorated compressor air seal, which resulted from inadequate maintenance inspection of the helicopter to detect corrosion in the compressor case while being… ## Docket (30 files) The files NTSB released with the investigation on October 5, 1999, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=30122. 16.0 MB in all. - Materials Laboratory Factual Report 99-53 (item 1, .PDF, 8.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416618&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2099-53-Redacted.PDF - Supplement S (item 2, .PDF, 44 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109620&FileExtension=.PDF&FileName=Supplement%20S-Master.PDF - Crewmember Statements (item 3, .PDF, 837 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416619&FileExtension=.PDF&FileName=Crewmember%20Statements-Redacted.PDF - Maps or Charts of Accident Area, Wreckage Diagrams (item 4, .PDF, 190 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109623&FileExtension=.PDF&FileName=Maps%20or%20Charts%20of%20Accident%20Area,%20Wreckage%20Diagrams-Master.PDF - Schematics of the Tail Rotor Drivershaft Coupling (item 5, .PDF, 151 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109624&FileExtension=.PDF&FileName=Schematics%20of%20the%20Tail%20Rotor%20Drivershaft%20Coupling-Master.PDF - Photos of an Exemplar Tail Rotor Driveshaft Coupling (item 6, .PDF, 93 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109625&FileExtension=.PDF&FileName=Photos%20of%20an%20Exemplar%20Tail%20Rotor%20Driveshaft%20Coupling%20-Master.PDF - Report from the United States Coast Guard (item 7, .PDF, 237 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416620&FileExtension=.PDF&FileName=Report%20from%20the%20United%20States%20Coast%20Guard-Redacted.PDF - Report from the American Samoa Police Department (item 8, .PDF, 902 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416621&FileExtension=.PDF&FileName=Report%20from%20the%20American%20Samoa%20Police%20Department-Redacted.PDF - Boeing Company Report (item 9, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416622&FileExtension=.PDF&FileName=Boeing%20Company%20Report-Redacted.PDF - Rolls-Royce Allison Report (item 10, .PDF, 950 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416623&FileExtension=.PDF&FileName=Rolls-Royce%20Allison%20Report-Redacted.PDF - Kamatics Corporation Materials Laboratory Report (item 11, .PDF, 190 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416624&FileExtension=.PDF&FileName=Kamatics%20Corporation%20Materials%20Laboratory%20Report-Redacted.PDF - Maintenance Work Order, Including Discrepancies (item 12, .PDF, 134 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416625&FileExtension=.PDF&FileName=Maintenance%20Work%20Order,%20Including%20Discrepancies-Redacted.PDF - Helicopter Operations Inspection Form (item 13, .PDF, 92 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416626&FileExtension=.PDF&FileName=Helicopter%20Operations%20Inspection%20Form-Redacted.PDF - Excerpt from the MDHC Maintenance Manual Regarding the Installation of the Tail Rotor Driveshaft with the Kamatics Coupling (item 14, .PDF, 225 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109633&FileExtension=.PDF&FileName=Excerpt%20from%20the%20MDHC%20Maintenance%20Manual%20Regarding%20the%20Installation%20of%20the%20Tail%20Rotor%20Driveshaft%20with%20the%20Kamatics%20Coupling-Master.PDF - Pilot's Certificates (item 15, .PDF, 683 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416627&FileExtension=.PDF&FileName=Pilot%27s%20Certificates-Redacted.PDF - Pilot's Employment Application (item 16, .PDF, 600 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416628&FileExtension=.PDF&FileName=Pilot%27s%20Employment%20Application-Redacted.PDF - Statement of Party Representatives to NTSB Investigation (item 17, .PDF, 374 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416629&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 18, .PDF, 84 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40416630&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Redacted.PDF - Photo 1. Overall view of the helicopter laying on its left side on the ship's forward deck following recovery. Photo from PAM. (item 19, .PDF, 46 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109638&FileExtension=.PDF&FileName=Photo%201.%20%20Overall%20view%20of%20the%20helicopter%20laying%20on%20its%20left%20side%20on%20the%20ship%27s%20forward%20deck%20following%20recovery.%20%20Photo%20from%20PAM.-Master.PDF - Photo 2. Closeup view of the helicopter on its left side. Photo from PAM. (item 20, .PDF, 45 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109639&FileExtension=.PDF&FileName=Photo%202.%20%20Closeup%20view%20of%20the%20helicopter%20on%20its%20left%20side.%20%20Photo%20from%20PAM.-Master.PDF - Photo 3. Closeup view of the rotor mast. Photo from McDonnell Douglas. (item 21, .PDF, 43 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109640&FileExtension=.PDF&FileName=Photo%203.%20%20Closeup%20view%20of%20the%20rotor%20mast.%20%20Photo%20from%20McDonnell%20Douglas.-Master.PDF - Photo 4. View of the engine after removal from the airframe. Photo from Allison. (item 22, .PDF, 43 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109641&FileExtension=.PDF&FileName=Photo%204.%20%20View%20of%20the%20engine%20after%20removal%20from%20the%20airframe.%20%20Photo%20from%20Allison.-Master.PDF - Photo 5. Closeup view of break in tail rotor driveshaft. Photo from McDonnell Douglas. (item 23, .PDF, 42 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109642&FileExtension=.PDF&FileName=Photo%205.%20%20Closeup%20view%20of%20break%20in%20tail%20rotor%20driveshaft.%20%20Photo%20from%20McDonnell%20Douglas.-Master.PDF - Photo 6. Closeup view of the broken coupling while still attached at the main transmission output pinion. Photo by McDonnell Douglas. (item 24, .PDF, 31 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109643&FileExtension=.PDF&FileName=Photo%206.%20%20Closeup%20view%20of%20the%20broken%20coupling%20while%20still%20attached%20at%20the%20main%20transmission%20output%20pinion.%20%20Photo%20by%20McDonnell%20Douglas.-Master.PDF - Photo 7. The tail rotor driveshaft with the coupling removed. Photo from McDonnell Douglas. (item 25, .PDF, 42 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109644&FileExtension=.PDF&FileName=Photo%207.%20%20The%20tail%20rotor%20driveshaft%20with%20the%20coupling%20removed.%20%20Photo%20from%20McDonnell%20Douglas.-Master.PDF - Photo 8. Both pieces of the tail rotor gearbox coupling, side by side. Photo from McDonnell Douglas. (item 26, .PDF, 53 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109645&FileExtension=.PDF&FileName=Photo%208.%20%20Both%20pieces%20of%20the%20tail%20rotor%20gearbox%20coupling,%20side%20by%20side.%20%20Photo%20from%20McDonnell%20Douglas.-Master.PDF - Photo 9. Piece of the transmission output gearshaft coupling from driveshaft side showing two separated pieces of flex coupling and their associated fractures. Photo from McDonnell Douglas. (item 27, .PDF, 47 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109646&FileExtension=.PDF&FileName=Photo%209.%20%20Piece%20of%20the%20transmission%20output%20gearshaft%20coupling%20from%20driveshaft%20side%20showing%20two%20separated%20pieces%20of%20flex%20coupling%20and%20their%20associated%20fractures.%20%20Photo%20from%20McDonnell%20Douglas.-Master.PDF - Photo 10. Piece of transmission output gear shaft coupling from driveshaft side showing the bending away from the rotor brake disc. Photo from McDonnell Douglas. (item 28, .PDF, 35 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109647&FileExtension=.PDF&FileName=Photo%2010.%20%20Piece%20of%20transmission%20output%20gear%20shaft%20coupling%20from%20driveshaft%20side%20showing%20the%20bending%20away%20from%20the%20rotor%20brake%20disc.%20%20Photo%20from%20McDonnell%20Douglas.-Master.PDF - Photo 11. Piece of transmission output gearshaft coupling from the rotor brake disc side. Note the smearing of the bolt heads. Photo from McDonnell Douglas. (item 29, .PDF, 47 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109648&FileExtension=.PDF&FileName=Photo%2011.%20%20Piece%20of%20transmission%20output%20gearshaft%20coupling%20from%20the%20rotor%20brake%20disc%20side.%20%20Note%20the%20smearing%20of%20the%20bolt%20heads.%20%20Photo%20from%20McDonnell%20Douglas.-Master.PDF - Photo 12. The two pieces of the transmission output coupling stacked together as they should be. Note that the bend on the rotor disc section is forward, toward the disc, and the bend on the driveshaft section is aft, away (item 30, .PDF, 43 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40109649&FileExtension=.PDF&FileName=Photo%2012.%20%20The%20two%20pieces%20of%20the%20transmission%20output%20coupling%20stacked%20together%20as%20they%20should%20be.%20%20Note%20that%20the%20bend%20on%20the%20rotor%20disc%20section%20is%20forward,%20toward%20the%20disc,%20and%20the%20bend%20on%20the%20driveshaft%20section%20is%20aft,%20away%20-Master.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.