Hiller UH-12E accident near Millen, Georgia, September 29, 2021
On September 29, 2021 at about 2:30 pm local time, a 1961 Hiller UH-12E (helicopter), registered N430NR, was substantially damaged in an accident during enroute (cruise) near Millen, Georgia. It was an aerial application (crop spraying) flight under agricultural flying rules (Part 137). 1 person had minor injuries. The weather was visual conditions (good weather).
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The NTSB's probable cause their words, unchanged
The improper reassembly of the tail rotor gearbox following maintenance, which resulted in fatigue failure of the input pinion gear shaft, and the subsequent loss of tail rotor drive.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 29, 2021 · about 2:30 pm local time
- Place
- Millen, Georgia · map
- Type
- Accident
- Injuries
- 1 person had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Hiller UH-12E, built 1961 · all UH-12Es on the register
- Registration
- N430NR · registry record · serial 2074
- Damage
- Substantial damage
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
The NTSB's narrative final · quoted from the NTSB record
During cruise flight, the pilot heard a “pop” sound followed by the engine accelerating to a high rpm. According to the pilot, the helicopter began spinning counterclockwise at a high rate; the cyclic stick would not move; and collective and pedal control inputs had no effect. The pilot continued his attempts to counteract the helicopter’s rotation as it descended to ground impact. Postaccident examination of the wreckage revealed that airframe damage was consistent with ground impact and that main rotor blade deformation and damage were consistent with powered impact with terrain. Damage to the tail rotor blades was consistent with the tail rotor not being under power at impact, and the tail rotor gearbox input pinion bevel gear was found fractured from its gear shaft. Metallurgical examination of the input pinion gear shaft revealed that it had fractured from fatigue. The fatigue cracking initiated at gouge marks on the outer surface of the cylindrical shaft and propagated through nearly the entirety of the shaft cross-section. The length of the fatigue cracks and the fine spacing of the striations were indicative of high cycle fatigue crack propagation. Review of maintenance records revealed that the tail rotor gearbox was disassembled, visually inspected, and reassembled about 330.3 hours before the accident. Based on the high cycle fatigue crack propagation and the presence of fatigue cracking on the majority of the fracture cross-section, it is likely the gouge marks on the input pinion gear shaft were created during reassembly of the tail rotor gearbox during this maintenance action. A loss of drive to the tail rotor would result in a clockwise, nose-right yaw of the helicopter due to the torque effect on the fuselage of the counterclockwise rotation of the main rotor. The sudden loss of tail rotor drive due to the fracture of the input pinion bevel gear would unload the powertrain of the power being used by the tail rotor, leading to a temporary increase of rotor rpm as well as engine rpm, consistent with the pilot’s report. Although the pilot reported that the helicopter began to spin counterclockwise, it is likely he misidentified the direction of yaw.
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
- Loss of control in flight during enroute (cruise)
- Sys/Comp malf/fail (non-power) during enroute (cruise) defining event
- Collision with terrain or object (not controlled flight into terrain) during uncontrolled descent
The NTSB's findings
- Aircraft › Aircraft propeller/rotor › Tail rotor drive system › Tail rotor gearbox › Incorrect service/maintenance
- Aircraft › Aircraft propeller/rotor › Tail rotor drive system › Tail rotor gearbox › Fatigue/wear/corrosion
- Aircraft › Aircraft propeller/rotor › Tail rotor drive system › Tail rotor gearbox › Failure
- Personnel issues › Task performance › Maintenance › Scheduled/routine maintenance › Maintenance personnel
Pilot
- Certificate: commercial pilot, private
- Ratings: single-engine land; rotorcraft: helicopter
- Flight time: 2,300 in this make and model; 130 in the last 90 days
- Last flight review: April 7, 2021
- Medical certificate: Class 2 (with waivers/limitations)
- Seat: left
- Injury: minor injuries
The aircraft
- Airframe total time: 9,466 hours
- Last inspection: 100-hour inspection, September 3, 2021
- Maximum gross weight: 2,800 lb
- Seats: 3
- Landing gear: fixed
- Engine: Lycoming VO-540-C2A (piston); 0 hours total
The flight
- Departed from: Metter GA
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 300° at 6 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 84°F (29°C), dew point 61°F (16°C)
- Altimeter: 30.02 inHg
- Observation at 1:55 pm from TBR, 16 miles away
Weather report (METAR): KTBR 291755Z AUTO 30006KT 10SM CLR 29/16 A3002 RMK AO2 T02940160 10294 20165
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flig | 1 |
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The docket at the NTSB holds the report as a PDF and the investigation's photographs and documents. This site never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number ERA21LA386.