Beechcraft H-35 N7975D
10 August 1999 · Swan Lake, Montana, United States · Serious injuries
Summary
On 10 August 1999 at about 23:30 local time, a Beechcraft H-35 registered N7975D was involved in an accident near Swan Lake, Montana, United States. 2 people were on board and 2 were seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.
The record
- Date
- at 23:30
- Classification
- Accident
- Location
- Swan Lake, Montana, United States
- Coordinates
- 47.7407, -113.7403
- Aircraft
- Beechcraft H-35
- Registration
- N7975D
- Category
- Airplane
- Engines
- 1
- Operator
- Not recorded
- Operating rule
- Part 91: General Aviation
- Purpose of flight
- Personal
- Phase of flight
- Not recorded
- Route
- Creston → Benchmark
- Aircraft damage
- Substantial
- Weather
- VMC
- Light
- Day
- NTSB number
- SEA99FA138
People
2 people were seriously injured.
| On board | Died | Serious | Minor | Uninjured |
|---|---|---|---|---|
| 2 | 0 | 2 | 0 | 0 |
Probable cause
Detonation/pre-ignition due to use of improper grade and type of fuel (automotive) and the pilot-in-command's failure to use proper fuel specified by manufacturer's directives.
Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.
Read the full NTSB narrative
The pilot observed a rpm overspeed with oil temperature rise. Throttling back relieved the overspeed situation; however, he observed a rapid loss of remaining power after turning back toward a potential emergency landing airstrip. He stated that the propeller had continued windmilling until impact. Pistons 1, 2, 4, 5, and 6 had few combustion deposits on their combustion faces. Piston 3 exhibited evidence of detonation, including a hole of about 1 inch diameter, and a combustion surface with the appearance of erosion. As originally manufactured, minimum octane requirement for this engine fuel was 91/96 octane. Teledyne Continental Motors amended the recommended fuel to 100 octane after 91/96 octane fuel became obsolete. Placards on the airplane fuel tanks stated that minimum fuel required was 100 octane. No evidence was found of a Supplemental Type Certificate for use of automotive gasoline in the subject airplane or engine. A sample of the automotive fuel removed from the airplane after the accident was tested: Research Octane Number was 94, Motor Octane Number was 83.8, and anti-knock index was 88.9. The pilot stated that he had been using automotive gasoline in the airplane for approximately 700 hours.
Quoted verbatim from the NTSB record.
Other Beechcraft H-35 accidents
| Date | Aircraft | Location | Operator | Outcome | Died |
|---|---|---|---|---|---|
| 15 Dec 2003 | Beechcraft H-35 | Mena, Arkansas, United States | - | Fatal | 1 |
| 5 Jul 1994 | Beechcraft H-35 | Jackson, Alabama, United States | - | Fatal | 2 |
| 14 Jul 2005 | Beechcraft H-35 | Oregon City, Oregon, United States | David A Laurini | No injuries | - |
| 30 May 1988 | Beechcraft H-35 | Phoenix, Arizona, United States | David B. Cassidy | Fatal | 1 |
| 13 May 1985 | Beechcraft H-35 | Owyhee Reserv., Idaho, United States | - | No injuries | - |
| 24 Jun 1983 | Beechcraft H-35 | Graceville, Minnesota, United States | - | No injuries | - |
Other accidents in this area
| Date | Aircraft | Location | Operator | Outcome | Died |
|---|---|---|---|---|---|
| 8 May 1999 | Eugene Hughes LANCAIR IV | Butte, Montana, United States | - | No injuries | - |
| 21 Oct 1999 | Maule M-5-235C | Laurel, Montana, United States | - | No injuries | - |
| 21 Oct 1999 | Beechcraft S35 | Melstone, Montana, United States | - | No injuries | - |
| 20 Oct 1999 | Piper PA-24-250 | Bozeman, Montana, United States | - | Minor injuries | - |
| 22 May 1999 | Cessna 182K | Kalispell, Montana, United States | - | No injuries | - |
| 6 Jun 1999 | D Wayne Smith WAYNCRAFT 14 | Libby, Montana, United States | - | Fatal | 1 |