ASN Wikibase Occurrence # 352848
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| Date: | Tuesday 10 August 1999 |
| Time: | 17:30 LT |
| Type: |  Beechcraft H-35 |
| Owner/operator: | Private |
| Registration: | N7975D |
| MSN: | D5265 |
| Total airframe hrs: | 5360 hours |
| Engine model: | Continental O-470G |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Swan Lake, MT -
 United States of America
|
| Phase: | En route |
| Nature: | Private |
| Departure airport: | Creston, MT |
| Benchmark, MT (3U7 | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
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.
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.
Accident investigation:
 |
|
Sources:
NTSB SEA99FA138
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 09-Mar-2024 06:44 | ASN Update Bot | Added |
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