Aerospatiale AS-350D accident near Avalon, California, December 28, 1999
On December 28, 1999 at about 6:50 pm local time, a Aerospatiale AS-350D (helicopter), registered N3593S, was destroyed in an accident near Avalon, California. It was an other work-use flight under general aviation rules (Part 91). 1 person was seriously injured and 6 people had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
A loose pneumatic fitting caused the engine to go to flight idle power at a low altitude, which resulted in a forced landing in hilly terrain.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- December 28, 1999 · about 6:50 pm local time
- Place
- Avalon, California · map
- Type
- Accident
- Injuries
- 1 person was seriously injured and 6 people had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Aerospatiale AS-350D AS350D · all AS-350Ds on the register
- Registration
- N3593S · no longer on the register · serial 1063
- Damage
- Destroyed
- Flight
- Other work-use flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The helicopter collided with terrain following a loss of engine power while maneuvering at low level on a sightseeing flight. As the helicopter passed about 250 feet above ground level (agl) over a ridgeline, the pilot began a descending and decelerating right turn to observe a herd of buffalo. About midway down the ridge, the low rotor rpm warning horn sounded. The pilot lowered collective and the horn stayed on. He noted the rotor speed was down between 300 and 320 rpm and concluded that he would have to make an immediate landing. The helicopter landed downslope at an estimated 10 to 15 mph, and the tail rotor struck the ground first. The helicopter pitched forward, continued to slide down the hill, collided with trees, and rolled onto its right side. An 80-psi check of the pneumatic system revealed two calibrated leaks and an additional leak. The attachment fitting for the P3 air accumulator on the governor pressure (Pg) line was 3/4 of a turn loose. The engine was removed and shipped to the manufacturer for testing. Several discrepancies due to damaged hardware were corrected during preparation for the test run. The engine was placed in a test stand and started normally. The engine completed a test protocol with no discrepancies noted. The P3 accumulator fitting was loosened and the engine immediately went to flight idle. The engine would not accelerate above idle power with the P3 accumulator fitting loose. Once the fitting was loosened less than finger tight, it continued to loosen to 3/4 to a full turn loose.
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: airline transport pilot
- Ratings: multi-engine land; single-engine land; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Flight time: 11,122 hours in all; 3,930 in this make and model
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: rgt
- Injury: minor injuries
The aircraft
- Airframe total time: 14,085 hours
- Last inspection: 100-hour inspection, December 9, 1999; 40 hours since
- Maximum gross weight: 4,300 lb
- Seats: 7
- Landing gear: fixed
- Engine: Lycoming LTS-101-A3A (turboshaft); 0 hours total
The flight
- Departed from: Avalon CA at 5:30 pm
- Runway 0
Weather at the time
- Light: daylight
- Wind: from 300° at 5 knots
- Visibility: 10 statute miles
- Sky: scat at 10,000 ft
- Temperature: 73°F (23°C), dew point 0°F (-18°C)
- Altimeter: 30.00 inHg
- Observation at 6:56 pm from LGB, 26 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 1 | 5 |
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.