WPR13FA243 · Hiller UH-12E
Hiller UH-12E · Accident: powerplant system/component malfunction/failure en route
From Pangborn Memorial Airport (EAT) to Pangborn Memorial Airport (EAT)
Event
- NTSB case
- WPR13FA243
- 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
Hiller UH-12E
- Aircraft type
- Hiller UH-12
- 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
- N99090
- Operator
- Holmes Jeff
- Onboard fatalities
- Unknown
- Route
- From Pangborn Memorial Airport (EAT), Wenatchee, WATo Pangborn Memorial Airport (EAT), Wenatchee, WA
- Aircraft age
- About 51 years (built 1962)
- 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
- Defining eventThe 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
- Powerplant system/component malfunction/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
- Aircraft › Aircraft power plant
- Aircraft › Aircraft propeller/rotor
- Aircraft › Fluids/miscellaneous hardware
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The pilot reported that, after takeoff, when he was 3 miles from the airport, he heard a noise above and behind him. The pilot immediately turned the helicopter back toward the airport; when about 1 mile away, he heard a second noise. The pilot continued to the airport and was hovering the helicopter about 4 feet above the ground when the main rotor head and blades separated from the helicopter, flew up into the air, and impacted the ground about 300 feet away. The helicopter impacted the ground hard, and the tailboom separated about midspan.
Postaccident examination revealed that the main transmission housing exhibited multiple fractures on its second stage planetary gear housing; the fractures were primarily orientated vertically and were through the thin-walled section of the housing. Analysis of these fracture surfaces revealed that the cracks were consistent with overstress from radial stresses. The transmission was disassembled and substantial damage was observed to the first stage planetary gear teeth and the input gear teeth. A high quantity of metallic chips and flakes were discovered at the bottom of the lower housing and throughout the first stage planetary assembly. All six bolts securing the bevel gear to the first stage planetary carrier were fractured. Only one of the six separated bolt heads remained secured with safety wiring. The six bolts were removed each bolt exhibited fatigue fracture features consistent with overstress, such as crack arrest and beach marks, that surrounded a center region. The fatigue cracks initiated along the thread roots of the bolts; these cracks were generally positioned about 180 degrees from each other, and were consistent with failure from reverse bending fatigue. After the bolts fractured, the bevel gear was unconstrained, leading to overstress fracture of the adjacent components. The fracture surface of the main rotor shaft was analyzed; the fracture surface was orientated 45 degrees from the longitudinal direction of the shaft, and the shaft was deformed to one side. All features were consistent with overstress failure in tension.
A complete set of maintenance records were not available for review, thus, it could not be determined if the bolts met installation requirements or if regular inspection of bolt tightness was met.
Probable cause
Fatigue failure of the six bolts that secured the bevel gear to the first stage planetary carrier, which caused the transmission to seize while the helicopter and main rotor were still operating.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR13FA243
- Event ID
- 20130526X13738
- Case number
- WPR13FA243
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
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: local date, investigation status. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 2013-05-26.
- API snapshot SHA-256: ef61b73f9e2973ae62a52d62b087009f0721200c2cb3c80a9656bed0653a69ce; retrieved 2026-09-15T21:39:47.465Z.