Robinson R22 BETA incident near Franklin, Wisconsin, April 27, 1998
On April 27, 1998 at about 8:00 pm local time, a Robinson R22 BETA (helicopter), registered N8331F, suffered minor damage in an incident near Franklin, Wisconsin. It was a flight of an unrecorded kind 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 mechanic's failure to follow the manufacturer's maintenance rebuilding instructions.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- April 27, 1998 · about 8:00 pm local time
- Place
- Franklin, Wisconsin · map
- Type
- Incident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Robinson R22 BETA · all R22 BETAs on the register
- Registration
- N8331F · no longer on the register · serial 2578
- Damage
- Minor damage
- Flight
- Flight of an unrecorded kind · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot said he felt an abnormal vibration in his helicopter during cruise flight. He said he reduced power and made a partial power auto-rotation to a normal landing in an open field. The on-scene investigation revealed that the tail rotor's hub bolt had fractured completely. The hub bolt attaches the tail rotor assembly to its drive shaft. Examination of the bolt revealed it had failed due to fatigue. Maintenance records showed the bolt had 168.3-hours on it since had been examined. It had been removed from the hub assembly so that new teeter bearings could be installed in the hub. The mechanic said he visually examined the bolt and believed it could be returned to service. The mechanic said he did not use the required teeter bearing alignment tool to reinstall the new bearings because the fit was not tight. He said he did not re-balance the tail rotor assembly afer the work had been done. Re-balancing is a required process according to the manufacturer's maintenance procedures. The mechanic said he told the customer to have it checked if he felt any vibration.
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: instructor: helicopter; rotorcraft: helicopter
- Flight time: 945 hours in all; 945 in this make and model; 220 in the last 90 days; 75 in the last 30 days; 880 as pilot in command
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: rgt
The aircraft
- Airframe total time: 889 hours
- Last inspection: 100-hour inspection, April 19, 1998; 34 hours since
- Maximum gross weight: 2,400 lb
- Seats: 2
- Landing gear: fixed
- Engine: Lycoming O-360 (piston); 0 hours total
The flight
- Departed from: MKE Milwaukee WI
- Flight plan: not recorded
- Runway 0
Weather at the time
- Light: dawn
- Wind: from 030° at 12 knots
- Visibility: 10 statute miles
- Sky: broken clouds at 25,000 ft; not recorded
- Temperature: 45°F (7°C), dew point 36°F (2°C)
- Observation at 7:56 pm from MKE, 10 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.