Hiller UH12E accident near Hanford, California, June 23, 2011
On June 23, 2011 at about 11:00 am local time, a Hiller UH12E (helicopter), registered N99579, was substantially damaged in an accident during takeoff near Hanford, California. It was a positioning flight under general aviation rules (Part 91). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The separation of the tail rotor drive gear shaft due to torsional fatigue of its threaded portion, which resulted in a loss of tail rotor control.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- June 23, 2011 · about 11:00 am local time
- Place
- Hanford, California · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Hiller UH12E · all UH12Es on the register
- Registration
- N99579 · registry record · serial 1733
- Damage
- Substantial damage
- Flight
- Positioning flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot reported that during a preflight inspection he observed a small oil leak originating where the tail rotor drive shaft attaches to the transmission. He said that, following a discussion with his boss, they decided to reposition the helicopter from a vehicle-mounted platform onto the ground so they could perform a more detailed examination of the oil leak. The pilot stated that following a normal engine start, he began to lift the helicopter off the platform and heard a "growling" sound originating from the transmission followed by an immediate loss of tail rotor control. The pilot said that the helicopter immediately began to rotate to the right as he rolled the throttle off and lowered the collective. Subsequently, the helicopter landed hard onto the ground adjacent to the truck and platform. Postaccident examination of the helicopter revealed that the tail rotor gear shaft was separated from the tail rotor drive shaft coupling. Metallurgical analysis of the fracture surface of the tail rotor gear shaft revealed that the fracture was consistent with fatigue cracking that emanated from multiple origins at the root portion of a thread on the threaded portion of the shaft. The fatigue crack origin exhibited signatures consistent with being open for an extended period of time compared to the other regions of the fracture face; the amount of time could not be determined. The fatigue crack eventually propagated around the gear shaft as torsional fatigue. No maintenance records for the helicopter were recovered during the course of the investigation, and therefore the amount of flight time on the tail rotor gear shaft was undetermined.
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
What happened, in order
- Sys/Comp malf/fail (non-power) during takeoff defining event
- Loss of control in flight during takeoff
- Collision with terrain or object (not controlled flight into terrain) during uncontrolled descent
The NTSB's findings
- cause Aircraft › Aircraft propeller/rotor › Tail rotor drive system › Tail rotor drive shaft › Fatigue/wear/corrosion
- cause Aircraft › Aircraft oper/perf/capability › Performance/control parameters › Directional control › Attain/maintain not possible
Pilot
- Certificate: commercial pilot
- Ratings: single-engine land; rotorcraft: helicopter
- Flight time: 15,400 hours in all; 800 in this make and model; 200 in the last 90 days; 60 in the last 30 days; 15,200 as pilot in command
- Last flight review: November 20, 2010
- Medical certificate: Class 2 (without waivers/limitations)
- Seat: rgt
- Injury: no injuries
The aircraft
- Airframe total time: 10,485 hours
- Last inspection: 100-hour inspection, June 14, 2011
- Maximum gross weight: 3,100 lb
- Seats: 3
- Landing gear: fixed
- Engine: Lycoming IO-540-C2A (piston); 0 hours total
- Operator: Central Valley Aviation Inc.
The flight
- Departed from: Hanford CA at 11:00 am
- Destination: Hanford CA
- Flight plan: none
Weather at the time
- Light: night
- Wind: from 330° at 8 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 73°F (23°C), dew point 46°F (8°C)
- Altimeter: 29.78 inHg
- Observation at 10:53 am from HJO, 5 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 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.