Enstrom F-28-F accident near Riverside, California, June 25, 1997
On June 25, 1997 at about 7:43 pm local time, a Enstrom F-28-F (helicopter), registered N99YC, was substantially damaged in an accident near Riverside, California (Riverside Municipal airport). It was a personal flight under general aviation rules (Part 91). 3 people had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
failure by unknown maintenance personnel to retorque the nuts on the retainer cover.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- June 25, 1997 · about 7:43 pm local time
- Place
- Riverside, California · Riverside Municipal · map
- Type
- Accident
- Injuries
- 3 people had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Enstrom F-28-F · all F-28-Fs on the register
- Registration
- N99YC · registry record · serial 809
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
During takeoff, the helicopter lost power and landed hard. Postaccident examination revealed the No. 2 cylinder intake valve rocker shaft migrated out of the shaft bosses of the cylinder head. The shaft, cover, and nuts were found; the washers were not. According to owner/pilot there were internal star washer imprints on the cover plate commonly caused by torque or tightening of the nut. The helicopter had 61.5 total hours since new, and received one 50-hour inspection since delivery to the owner/pilot. The owner/pilot changed the oil and filter just prior to the 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: commercial pilot
- Ratings: multi-engine land; multi-engine sea; single-engine land; single-engine sea; instrument: airplane; rotorcraft: glider; rotorcraft: gyroplane; rotorcraft: helicopter
- Flight time: 2,500 hours in all
- Medical certificate: Class 3 (valid medical--w/ waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 61 hours
- Last inspection: inspection type not recorded, May 19, 1997; 1 hours since
- Maximum gross weight: 1,950 lb
- Seats: 3
- Landing gear: fixed
- Engine: Lycoming HIO-360-F1AD (piston); 0 hours total
- Operator: Stits Aircraft
The flight
- Departed from: RAL CA at 7:40 pm
- Destination: L66 Corona CA
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Wind: from 300° at 9 knots
- Visibility: 4 statute miles
- Sky: clear
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
- Observation at 7:47 pm from KRA
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 2 |
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.