CHI98IA136 · Robinson R22 BETA
Robinson R22 BETA · Incident: airframe, component or system failure en route
From General Mitchell International Airport (MKE) to an unrecorded destination
Event
- NTSB case
- CHI98IA136
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Incident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Robinson R22 BETA
- Aircraft type
- Robinson R22
- Category
- Helicopter
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N8331F
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From General Mitchell International Airport (MKE), Milwaukee, WITo not recorded
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route · cruise
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Airframe, component or system failure
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Minor
Cause areas
- Other maintenance personnel › Maintenance, rebuild/remanufacture, not complied with
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
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.
Probable cause
The mechanic's failure to follow the manufacturer's maintenance rebuilding instructions.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record CHI98IA136
- Event ID
- 20001211X09809
- Case number
- CHI98IA136
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 5cf2f4f24e9dcdbf51be26b1cd83b034b7b4c95b48ab2edba0346644e1f8f5a4; retrieved 2026-09-22T17:50:31.150Z.