Bell 47D1 accident near San Diego, California, November 8, 2011
On November 8, 2011 at about 10:25 pm local time, a Bell 47D1 (helicopter), registered N4251A, was substantially damaged in an accident near San Diego, California (Brown Field). It was an instructional flight under general aviation rules (Part 91). No one was hurt; 2 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The flight instructor's inadequate supervision of the student pilot during a simulated autorotation and the pilots’ failure to use carburetor heat while operating at reduced engine power while in carburetor icing conditions, which resulted in a loss of engine power.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- November 8, 2011 · about 10:25 pm local time
- Place
- San Diego, California · Brown Field · map
- Type
- Accident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell 47D1 · all 47D1s on the register
- Registration
- N4251A · no longer on the register · serial 110
- Damage
- Substantial damage
- Flight
- Instructional flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
During an instructional flight, a practice autorotation was initiated with the intention of performing a power recovery. The student maintained directional control while the certified flight instructor (CFI) adjusted the rotor rpm. The student initiated the power recovery, but the engine did not respond. The student then relinquished control of the helicopter to the CFI, who attempted to cushion the landing, but the helicopter landed hard. The helicopter's engine was equipped with a float-type carburetor, and the weather conditions provided for the possibility of serious carburetor icing at glide power. The accumulation of carburetor ice likely resulted in the loss of engine power. Neither the CFI nor student applied carburetor heat during the autorotation, nor they did not monitor the carburetor temperature gauge during the maneuver. During the postaccident examination of the engine, no mechanical failures or malfunctions were revealed which would have precluded normal operation. The CFI's flight experience in piston-powered helicopters was limited to the 6 hours of training he had provided in the accident helicopter, with his prior rotorcraft experience occurring exclusively in turbine-powered helicopters. This was also the first time he had performed an autorotation in the accident helicopter.
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
- Autorotation Loss of engine power (total) defining event
- Hard landing during landing (flare/touchdown)
The NTSB's findings
- cause Personnel issues › Action/decision › Action › Delayed action › Instructor/check pilot
- cause Aircraft › Aircraft systems › Ice/rain protection system › Intake anti › ice, deice › Not used/operated
- cause Personnel issues › Task performance › Use of equip/info › Use of equip/system › Pilot
- Personnel issues › Experience/knowledge › Experience/qualifications › Total experience › Instructor/check pilot
- cause Environmental issues › Conditions/weather/phenomena › Temp/humidity/pressure › Conducive to carburetor icing › Decision related to condition
Flight instructor
- Certificate: flight instructor, commercial pilot, military
- Ratings: multi-engine land; single-engine land; instructor: airplane single-engine; instructor: helicopter; instructor: instrument airplane; instructor: instrument helicopter; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Flight time: 5,650 hours in all; 6 in this make and model; 17 in the last 90 days; 14 in the last 30 days; 4,200 as pilot in command; 2,259 on instruments
- Last flight review: September 23, 2011
- Medical certificate: Class 2 (without waivers/limitations)
- Seat: rgt
- Injury: no injuries
Dual student
- Certificate: private
- Ratings: single-engine land; instrument: airplane; rotorcraft: helicopter
- Flight time: 700 hours in all; 6 in this make and model; 6 in the last 90 days; 6 in the last 30 days; 610 as pilot in command
- Last flight review: November 14, 2010
- Medical certificate: Class 3 (without waivers/limitations)
- Seat: left
- Injury: no injuries
The aircraft
- Airframe total time: 4,727 hours
- Last inspection: annual inspection, October 3, 2011; 10 hours since
- Maximum gross weight: 2,200 lb
- Seats: 2
- Landing gear: fixed
- Engine: Franklin 6V4 SERIES (piston); 0 hours total
The flight
- Departed from: SDM San Diego CA at 9:20 pm
- Destination: SDM San Diego CA
- Flight plan: none
- Runway 26L, 3,180 ft by 75 ft
- A second pilot was aboard
Weather at the time
- Light: daylight
- Wind: from 290° at 8 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 64°F (18°C), dew point 37°F (3°C)
- Altimeter: 30.14 inHg
- Observation at 10:53 pm from SDM
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 2 |
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 N4251A 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.