DEN99LA040 · Hughes 369D
Hughes 369D · Accident: total loss of engine power (mechanical failure) while maneuvering
From WY (no airport) to an unrecorded destination
Event
- NTSB case
- DEN99LA040
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Hughes 369D
- Aircraft type
- Hughes 369
- Category
- Helicopter
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- CGDCM
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From WY (no airport)To not recorded
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Maneuvering
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Total loss of engine power (mechanical failure)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Pilot in command › Rotor RPM, not maintained
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The helicopter was conducting a seismic survey operation at 200 to 250 feet agl at 40 knots when the engine's automatic re-ignition system caution light illuminated, followed by an immediate loss of main rotor rpm. The pilot unsuccessfully attempted to perform an autorotation, and the aircraft impacted the ground. A postaccident examination of the turboshaft engine was performed, revealing that the PC line 'B' nut between the fuel control unit (FCU) and the power turbine governor (PTG) was not connected at the FCU, resulting in a loss of engine pneumatic pressure. According to aircraft maintenance records, the turbine section of the engine was removed by company maintenance and replaced with a rental turbine. The PC line and various pneumatic and fuel system lines had been removed to facilitate removal and replacement of the engine's turbine section. The helicopter had flown 6.1 hours since the turbine was replaced.
Probable cause
A hard landing resulting from rotor rpm decay. Factors were the improper replacement of the turbine by company maintenance personnel resulting in the PC line nut becoming loose, and the pilot operating outside the normal height/velocity curve.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record DEN99LA040
- Event ID
- 20001205X00151
- Case number
- DEN99LA040
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: local date, investigation status. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 1999-02-16.
- API snapshot SHA-256: c6829bb400383a9a458a54179fa7a606647f32c02d58d77ce6f6d0edf9de1e0b; retrieved 2026-09-21T11:12:00.355Z.