Hiller UH-12C accident near Grafton, Ohio, May 16, 1999
On May 16, 1999, a Hiller UH-12C (helicopter), registered N812WC, was substantially damaged in an accident near Grafton, Ohio. It was a personal 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
Inadequate maintenance which resulted in the failure of the mercury clutch assembly.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- May 16, 1999
- Place
- Grafton, Ohio · 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
- N812WC · no longer on the register · serial 1038
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
About 500 feet above ground level, and 10 minutes before landing, the pilot noticed a change in main rotor noise. The engine rpm increased, and rotor rpm decreased. The pilot reduced collective and increased throttle, but engine rpm continued to increase, and rotor rpm continued to decrease. The pilot entered an autorotation, the helicopter impacted a wire, and then came to rest upright. Inspection of the mercury clutch revealed a 'minor' leak from the transmission sun gear seal, but no oil was discovered on the clutch shoes. In addition, the intermediate drive shaft teeth were 'severely' worn, and three of the teeth had broken corners. The clutch shoes were worn beyond limits, and were glazed consistent with overheating. One clutch return spring was broken. The driver slots in the clutch side plates were 'severely' worn, and the driver lugs were also 'severely' worn. All the clutch attaching hardware were 'improperly' safetied, using .031 inch safety wire, and 'numerous' fasteners were safetied backwards. The clutch was a conditional item. Since the last 100 hour inspection on March 12, 1999, the helicopter flew 100 hours.
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
- Ratings: single-engine land; rotorcraft: helicopter
- Flight time: 5,410 hours in all; 80 in the last 90 days; 30 in the last 30 days; 5,347 as pilot in command
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 7,860 hours
- Last inspection: 100-hour inspection, November 9, 1998; 100 hours since
- Maximum gross weight: 2,500 lb
- Seats: 3
- Landing gear: fixed
- Engine: Franklin 6V-335-B (piston); 0 hours total
The flight
- Departed from: NONE Findlay OH
- Destination: 4G8 Columbia OH
- Flight plan: none
- Runway 0
Weather at the time
- Light: night, dark
- Wind: from 130° at 12 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 75°F (24°C), dew point 46°F (8°C)
- Altimeter: 30.00 inHg
- Observation at 8:54 pm from CLE, 24 miles away
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.