Hiller UH12D accident near Sparks, Nevada, August 25, 1991
On August 25, 1991 at about 2:50 am local time, a Hiller UH12D (helicopter), registered N100HH, was substantially damaged in an accident near Sparks, Nevada. It was a personal flight under general aviation rules (Part 91). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
THE ENCOUNTER WITH ROUGH, UNSUITABLE TERRAIN DURING A PRECAUTIONARY LANDING. CONTRIBUTING TO THE ACCIDENT WAS THE PILOT'S DECISION TO MAKE AN AUTOROTATION AFTER ENCOUNTERING AN AIRFRAME VIBRATION.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- August 25, 1991 · about 2:50 am local time
- Place
- Sparks, Nevada · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Hiller UH12D · all UH12Ds on the register
- Registration
- N100HH · registry record · serial 1266
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
THE CERTIFICATED PRIVATE HELICOPTER PILOT, THE SOLE OCCUPANT, WAS ON A LOCAL AREA FLIGHT WHEN A STRONG, MEDIUM TO HIGH FREQUENCY VIBRATION DEVELOPED IN THE TAIL SECTION OF HIS HELICOPTER. THE PILOT ELECTED TO MAKE A PRECAUTIONARY LANDING IN AN OPEN DIRT AREA, AND EXECUTED AN AUTOROTATION. AFTER TOUCHDOWN THE HELICOPTER SLID ON ROUGH, ROCKY TERRAIN, CAUSING THE MAIN ROTOR BLADES TO CONTACT THE TAIL BOOM. THREE FEET OF THE TAIL BOOM INCLUDING THE TAIL ROTOR GEAR BOX AND BLADES, AND THE TAIL ROTOR DRIVE SHAFT WERE SEVERED. AN EXAMINATION OF THE TAIL ROTOR DRIVE SHAFT AT THE POSITION WHERE A SUPPORT BEARING IS MOUNTED, REVEALED SIGNS OF HEAT AND WEAR. DURING THE IMPACT SEQUENCE, THE DRIVE SHAFT SUPPORT BEARING DEPARTED THE HELICOPTER AND WAS NOT RECOVERED.
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: private
- Ratings: rotorcraft: helicopter
- Flight time: 265 hours in all; 5 in the last 90 days; 2 in the last 30 days; 265 as pilot in command
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: ctr
The aircraft
- Airframe total time: 5,868 hours
- Last inspection: annual inspection, March 12, 1991; 10 hours since
- Maximum gross weight: 3,100 lb
- Seats: 3
- Landing gear: fixed
- Engine: Lycoming VO-435-AIC (piston); 0 hours total
- Operator: Pathfinder Technology INC.
The flight
- Departed from: NONE Reno NV at 1:50 am
- Destination: 45D Stead NV
- Flight plan: none
- Runway 0
Weather at the time
- Light: dusk
- Wind: from 270° at 5 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 81°F (27°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 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.