FTW98LA253 · Hiller UH-12E
Hiller UH-12E · Accident: airframe, component or system failure while maneuvering
Event
- NTSB case
- FTW98LA253
- 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
- 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
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
- N4028T
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From not recordedTo 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 137: Agricultural
- 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
- Maneuvering · aerial application
- 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
- Lubricating system, oil filter/screen › Flow restricted
- Rotor drive system, main gearbox/transmission › Failure, total
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The helicopter was traveling in an easterly direction at an airspeed of 60 knots, while maintaining a constant 5 foot clearance over the rice field, when the transmission failed. The pilot turned the helicopter to the right to avoid a tall tree, as he simultaneously initiated a forced landing. During the touchdown on soft ground, both skids and the collapsed and the tailboom was severed by the main rotor blades. According to the maintenance records, the main transmission (part number 23700-9, serial number 617), which has a recommended TBO of 1,200 hours, had accumulated 1,048 hours since its last overhaul in 1993. According to the manufacturer, the 23700-9 transmissions are subject to a recurring inspection of the oil filter every 50 flight hours in accordance with Airworthiness Directive 81-17-03. According to the maintenance logbooks, the last compliance with AD 81-17-03 was 340 hours prior to the accident, on March 26, 1996. Examination of the transmission by the manufacturer's representative revealed a massive failure of the first stage planetary gear system due to lack of lubrication.
Probable cause
The failure of maintenance personnel to comply with and airworthiness directive, which resulted in failure of the planetary gear due to lack of lubrication. A contributing factors was the lack of suitable terrain for the pilot to execute a forced landing.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record FTW98LA253
- Event ID
- 20001211X10302
- Case number
- FTW98LA253
- 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: 624835173d376e40b256559d7a887f896f5b2c826c59818ad5504e1fb5f490d7; retrieved 2026-09-22T17:43:00.073Z.