Hughes 369HS accident near Pacific Ocean, PO, June 16, 1998
On June 16, 1998 at about 2:00 pm local time, a Hughes 369HS (helicopter), registered N95MS, was destroyed in an accident near Pacific Ocean, PO. It was an aerial observation flight under general aviation rules (Part 91). 2 people were killed. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- June 16, 1998 · about 2:00 pm local time
- Place
- Pacific Ocean, PO
- Type
- Accident
- Injuries
- 2 people were killed.
- Weather
- visual conditions (good weather)
- Aircraft
- Hughes 369HS · all 369HSs on the register
- Registration
- N95MS · registry record · serial 1130536S
- Damage
- Destroyed
- Flight
- Aerial observation flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
Pilot
- Certificate: commercial pilot, private
- Ratings: multi-engine land; single-engine land; instrument: airplane; rotorcraft: helicopter
- Flight time: 1,120 hours in all; 260 in this make and model
- Medical certificate: Class 1 (valid medical--no waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 6,018 hours
- Last inspection: annual inspection, May 18, 1998; 29 hours since
- Maximum gross weight: 2,550 lb
- Seats: 4
- Landing gear: fixed
- Engine: Allison 250-C20B (turboshaft); 0 hours total
The flight
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Wind: from 090° at 5 knots
- Visibility: 12 statute miles
- Sky: clear
- Temperature: 84°F (29°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Other NTSB records under N95MS the same tail number, which may have belonged to a different aircraft at the time
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The documents and photographs are the NTSB's docket, the folder of records gathered during the investigation, shown as the NTSB released them (the NTSB redacts some personal details first) and listed under the NTSB's own titles. This site's own text never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number LAX98LA200.