Individually Owned: 150,657
Corporate Owned: 137,281
Aircraft Accident/Incident Report
Swan Lake, Montana 59911
Tuesady, August 10, 1999 17:30 MDT
NTSB Narrative Summary Released at Completion of Accident
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.
NTSB Probable Cause Narrative
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.
Event Information
| Type of Event | Accident |
| Event Date | 8/10/1999 |
| Event Day of the Week | Tuesday |
| Time of Event | 1730 |
| Event Time Zone | Mountain Daylight Time |
| Event City | SWAN LAKE |
| Event State | MONTANA |
| Event Country | -- |
| Zipcode of the event site | 59911 |
| Event Date Year | 1999 |
| Event Date Month | 8 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | |
| Event Location Longitude | |
| Event Location Airport | |
| Event Location Nearest Airport ID | |
| Indicates whether the acc/inc occurred off or on an airport | Off Airport/Airstrip |
| Distance from airport in statute miles | -- |
| Degrees magnetic from airport | -- |
| Airport Elevation | -- |
| Weather Briefing Completeness | Not pertinent |
| Investigator's weather source | Pilot |
| Time of the weather observation | 0 |
| Direction of event from weather observation facility (degrees) | 0 |
| Weather Observation Facility ID | |
| Elevation of weather observation facility | 0 |
| Distance of event from weather observation facility (units?) | 0 |
| Time Zone of the weather observation | |
| Lighting Conditions | Day |
| Lowest Ceiling Height | 0 |
| Lowest Non-Ceiling Height | 0 |
| Sky/Lowest/Cloud Conditions | Clear |
| Sky Condition for Lowest Ceiling | None |
| Visibility Runway Visual Range (Feet) | 0 |
| Visibility Runway Visual Value (Statute Miles) | 0 |
| Visibility (Statute Miles) | 15 |
| Air Temperature at event time (in degrees celsius) | 32 |
| Dew Point at event time (in degress fahrenheit) | -- |
| Wind Direction (degrees magnetic) | 0 |
| Variable Wind Indicator | Unknown |
| Wind Speed (knots) | 0 |
| Wind Velocity Indicator | Unknown |
| Wind Gust Indicator | Unknown |
| Wind Gust (knots) | 0 |
| Altimeter Setting at event time (in. Hg) | -- |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | Unknown |
| METAR weather report | -- |
| Event Highest Injury | Serious |
| On Ground, Fatal Injuries | 0 |
| On Ground, Minor Injuries | 0 |
| On Ground, Serious Injuries | 0 |
| Injury Total Fatal | -- |
| Injury Total Minor | -- |
| Injury Total None | -- |
| Injury Total Serious | 2 |
| Injury Total All | 2 |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 996 |
| NTSB Notification Source | -- |
| NTSB Notification Date | Aug 10 1999 12:00AM |
| NTSB Notification Time | 2030 |
| Fiche Number and/or location -used to find docket information | IMAGE |
| Date of most recent change to record | Jan 10 2001 10:17AM |
| User who most recently changed record | dbo |
| Basic weather conditions | Visual Meteorological Cond |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N7975D |
| NTSB Number | SEA99FA138 |
| Missing Aircraft Indicator | N |
| Federal Aviation Reg. Part | Part 91: General Aviation |
| Type of Flight Plan filed | None |
| Flight plan Was Activated? | -- |
| Damage | Substantial |
| Aircraft Fire | None |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | Beech |
| Aircraft Model | H-35 |
| Aircraft Series Identifier | H-35 |
| Aircraft Serial Number | D5265 |
| Certified Max Gross Weight | 2900 |
| Aircraft Category | Airplane |
| Aircraft Registration Class | U.S. Registered/U.S. Soil |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | -- |
| Total number of seats on the aircraft | 4 |
| Number of Engines | 1 |
| Fixed gear or retractable gear | Retractable |
| Aircraft, Type of Last Inspection | Annual |
| Date of Last Inspection | Apr 23 1999 12:00AM |
| Airframe hours since last inspection | 10 |
| Airframe Hours | 5360 |
| ELT Installed | Yes |
| ELT Activated | Yes |
| ELT Aided Location of Event Site | No |
| ELT Type | -- |
| Aircraft Owner Name | PAUL L. WELLS |
| Aircraft Owner Street Address | 50 WEST 2ND STREET |
| Aircraft Owner City | WHITEFISH |
| Aircraft Owner State | MT |
| Aircraft Owner Country | |
| Aircraft Owner Zipcode | 59937 |
| Operator is an individual? | -- |
| Operator Name | |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | Yes |
| Operator Street Address | |
| Operator City | |
| Operator State | |
| Operator Country | |
| Operator Zip code | |
| Operator Code | |
| Owner has at least one certificate | None |
| Other Operator of large aircraft? | No |
| Certified for Part 133 or 137 Operation | Unknown |
| Operator Certificate Number | -- |
| Indicates whether an air carrier operation was scheduled or not | -- |
| Indicates Domestic or International Flight | -- |
| Operator carrying Pax/Cargo/Mail | -- |
| Type of Flying (Per_Bus / Primary) | Personal |
| Second Pilot on Board | No |
| Departure Point Same as Event | No |
| Departure Airport Code | |
| Departure City | CRESTON |
| Departure State | MT |
| Departure Country | |
| Departure Time | 1700 |
| Departure Time Zone | MDT |
| Destination Same as Local Flt | -- |
| Destination Airport Code | 3U7 |
| Destination City | BENCHMARK |
| Destination State | MT |
| Destination Country | |
| Specific Phase of Flight | -- |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | Jan 10 2001 12:27PM |
| User who most recently changed record | dbo |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | 0 |
| Runway Length | -- |
| Runway Width | -- |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |