Hiller UH-12E accident near Dos Palos, California, September 1, 1995
On September 1, 1995 at about 3:30 pm local time, a Hiller UH-12E (helicopter), registered N4027D, was substantially damaged in an accident near Dos Palos, California. It was an aerial application (crop spraying) flight under agricultural flying rules (Part 137). 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 fatigue failure of the tail rotor tension torsion bar plates.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 1, 1995 · about 3:30 pm local time
- Place
- Dos Palos, California · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Hiller UH-12E · all UH-12Es on the register
- Registration
- N4027D · registry record · serial 5072
- Damage
- Substantial damage
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
The NTSB's narrative final · quoted from the NTSB record
THE PILOT WAS SPRAYING A TOMATO FIELD WHEN A STRONG VIBRATION STARTED THROUGH THE AIRFRAME, FOLLOWED IMMEDIATELY BY A SEVERE YAW. PEDAL INPUT HAD NO EFFECT ON THE YAW AND THE HELICOPTER BEGAN TO SPIN. THE PILOT REDUCED POWER AND LOWERED THE COLLECTIVE TO STOP THE YAW AND THE HELICOPTER LANDED HARD. AN FAA AIRWORTHINESS INSPECTOR EXAMINED THE WRECKAGE AT THE ACCIDENT SITE. ONE TAIL ROTOR BLADE WAS MISSING AND SUBSEQUENTLY FOUND ABOUT 100 FEET AWAY. THE INSPECTOR REPORTED THAT THE TENSION TORSION (TT) PLATES OF THE SEPARATED BLADE WERE BROKEN AT THE HUB ATTACH BOLTS. NO LEADING EDGE DAMAGE WAS OBSERVED ON THE BLADE. THE FRACTURED TT PLATES WERE SENT TO THE NTSB LAB WHERE REPRESENTATIVE PLATE FRACTURES WERE SELECTED FOR DETAILED EXAMINATION. FEATURES TYPICAL OF PROGRESSIVE FATIGUE CRACKING WERE OBSERVED. A MATERIAL ANALYSIS REVEALED THAT THE STRAPS WERE MADE FROM THE MANUFACTURER'S SPECIFIED MATERIAL. NO EVIDENCE OF FOREIGN ELEMENT CONTAMINATION WAS FOUND ON THE FRACTURE FACES. THE TAIL ROTOR TT BAR HAS A 12,500-HOUR LIFE LIMIT AND THE FRACTURED TT BAR HAD ACCUMULATED A TOTAL TIME IN SERVICE OF 3,710 HOURS. NO PRIOR INCIDENTS WERE FOUND IN THE FAA SERVICE DIFFICULTY REPORT DATA BASE.
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
Pilot
- Certificate: commercial pilot
- Ratings: multi-engine land; single-engine land; single-engine sea; rotorcraft: helicopter
- Flight time: 8,500 hours in all; 3,003 in this make and model; 300 in the last 90 days; 70 in the last 30 days; 8,390 as pilot in command
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: ctr
The aircraft
- Airframe total time: 2,749 hours
- Last inspection: 100-hour inspection, August 22, 1995; 24 hours since
- Maximum gross weight: 3,100 lb
- Seats: 3
- Landing gear: fixed
- Engine: Lycoming VO-540-C2A (piston); 0 hours total
The flight
- Departed from: 0M9 Delhi CA at 1:00 pm
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Visibility: 30 statute miles
- Sky: clear
- Temperature: 68°F (20°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| 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.
Other NTSB records under N4027D the same tail number, which may have belonged to a different aircraft at the time
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.