Bell 47G-4A accident near Bakersfield, California, April 3, 2004
On April 3, 2004 at about 3:45 pm local time, a Bell 47G-4A (helicopter), registered N7NB, was substantially damaged in an accident near Bakersfield, California. It was an aerial application (crop spraying) flight under agricultural flying rules (Part 137). 1 person was seriously injured. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
a loss of tail rotor drive due to a disconnection of the drive shaft's splined coupling at the tail rotor gear box. The splined coupling to tail rotor gear box disconnection occurred as a result of tail boom flexing due to the combined effects of an uninstalled structural support tube and a crack in left side frame tubes. Inadequate maintenance inspection was a factor.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- April 3, 2004 · about 3:45 pm local time
- Place
- Bakersfield, California · map
- Type
- Accident
- Injuries
- 1 person was seriously injured.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell 47G-4A · all 47G-4As on the register
- Registration
- N7NB · registry record · serial 7732
- 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 helicopter experienced a loss of tail rotor control and collided with terrain. During an aerial application flight, the pilot heard a rattling noise from the aft end of the helicopter. He then lost tail rotor authority and entered a flat spin. The pilot attempted to make a run-on landing, but the helicopter continued to spin until it impacted terrain. A Federal Aviation Administration inspector examined the helicopter after the accident. He noted that the cross-over support tube near the aft end of the tail boom was missing. A crack was found on the tail boom left side frame tubes. Deposits of rust in the area suggests that the crack was a pre-existing crack. The inspector thought that this would have added excessive stress to the structure during turning maneuvers and caused the last spline coupling shaft to disconnect from the tail rotor gear box as the tail boom flexed. A 50-hour maintenance inspection was completed the day before the accident.
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; rotorcraft: helicopter
- Flight time: 3,833 hours in all; 1,800 in this make and model; 173 in the last 90 days; 73 in the last 30 days
- Last flight review: January 15, 2004
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: left
- Injury: serious injuries
The aircraft
- Airframe total time: 9,916.2 hours
- Last inspection: 100-hour inspection, April 2, 2004
- Maximum gross weight: 2,950 lb
- Seats: 1
- Landing gear: fixed
- Engine: Lycoming VO-540-B1B3 (piston); 0 hours total
The flight
- Departed from: KMIT Shafter CA at 3:00 pm
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: at 0 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 63°F (17°C), dew point 43°F (6°C)
- Altimeter: 29.93 inHg
- Observation at 3:54 pm from BFL
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.
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.