Hiller UH-12C accident near Clinton, Iowa, October 24, 1998
On October 24, 1998 at about 4:30 pm local time, a Hiller UH-12C (helicopter), registered N9739C, was substantially damaged in an accident near Clinton, Iowa. It was a business flight under general aviation rules (Part 91). No one was hurt; 2 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
the failure of the 90 degree gearbox for reasons undetermined. Factors were the failure of the gearbox, and it not being possible for the pilot to maintain control of the aircraft.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- October 24, 1998 · about 4:30 pm local time
- Place
- Clinton, Iowa · map
- Type
- Accident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Hiller UH-12C · all UH-12Cs on the register
- Registration
- N9739C · registry record · serial 847
- Damage
- Substantial damage
- Flight
- Business flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
During cruise flight the helicopter suffered a loss of tail rotor authority. The pilot initiated an autorotational landing; however, during the approach he lost all control of the aircraft. An inspection of the tail rotor gearbox after the accident revealed a failure of the 90 degree gearbox. The log books indicated an overhaul 195 hours prior to the accident with no other maintenance on the gearbox noted. An inspection of the helicopter was conducted one month prior to the accident and the helicopter had accumulated about 33 hours since that inspection.
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: flight instructor, commercial pilot
- Ratings: single-engine land; instructor: helicopter; instrument: helicopter; rotorcraft: helicopter
- Flight time: 475 hours in all; 173 in this make and model; 8 in the last 90 days; 8 in the last 30 days; 362 as pilot in command; 15 on instruments
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 3,300 hours
- Last inspection: annual inspection, September 30, 1998; 33 hours since
- Landing gear: fixed
- Engine: Franklin 6V335-50 (piston); 0 hours total
The flight
- Departed from: CWI Clinton IA at 4:20 pm
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Wind: from 210° at 6 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 64°F (18°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.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.