CHI03FA025 · Robinson R22
Robinson R22 · Accident: airframe, component or system failure en route
From St Louis Downtown Airport (CPS) to an unrecorded destination
Event
- NTSB case
- CHI03FA025
- 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
- Accident
- 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
- Unknown
- 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
- 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
- N559DD
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From St Louis Downtown Airport (CPS), Cahokia/St. Lou, ILTo 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
- Substantial
Cause areas
- Rotor drive system › Failure, total
- Rotor drive system, clutch assembly › Fatigue
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
The helicopter was substantially damaged when the fan shaft failed causing a loss of power to the main and tail rotors. The instructor pilot reported that while in cruise flight the clutch light flickered several times. He stated that he pulled the clutch circuit breaker, "however the noise continued to worsen and [he] suspected the drive belts were loosening." He reset the clutch circuit breaker and the clutch light illuminated steadily. The instructor pilot reported, "Immediately afterward the engine and rotor RPM needles split indicating a drive train failure, and a loud metal to metal grinding noise began." The flight crew (instructor and dual student) immediately initiated an autorotation. At the termination of the autorotation, the helicopter yawed to the left and did not respond to right pedal inputs. A post-accident examination revealed a complete failure of the fan shaft. The portion of the engine cooling fan assembly aft of the fracture point had departed the aircraft. This component was subsequently found approximately 1.2 miles south of the forced landing site. In addition, the tail rotor blade pitch push-pull tube was completely severed at the forward rod end. Extensive scraping and gouging was noted on the rod end fitting. The fan shaft, fan wheel and bearing were sent to the NTSB Materials Laboratory for examination. The examination noted the fan shaft was fractured in a "V"shape from a transition in shaft diameter adjacent to the bearing at the aft end, forward to the attachment bolt holes. Fracture surface features were "indicative of fatigue propagation." According to the dual student, on the delivery flight one of the drive v-belts broke and an emergency landing under partial power was made. The helicopter was repaired by Robinson technicians who replaced the drive belts and clutch actuator. A visual inspection of the fan shaft and lower bearing was completed at that time and no discrepancies were found. The fan shaft and bearing were not disassembled. Therefore, the mating surfaces of the fan shaft and bearing race were not inspected.
Probable cause
Fatigue fracture of the clutch assembly fan shaft and the resulting complete loss of power to the rotor drive system. A contributing factor was the loss of tail rotor authority due to the secondary failure of the control tube assembly.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record CHI03FA025
- Event ID
- 20021202X05545
- Case number
- CHI03FA025
- 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, coordinates. 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: 9392d5e2361fa6b3803447c5d17b8d14435c7131383c14e59628f075067c5a78; retrieved 2026-09-22T09:55:10.525Z.