# NTSB Accident SEA99FA138
> **Beech H-35** · 1999-08-10 · SWAN LAKE, MT, USA · SERS
## Event
- **NTSB number:** SEA99FA138
- **Event ID:** 20001212X19640
- **Type:** Accident
- **Date:** 1999-08-10
- **Location:** SWAN LAKE, MT, USA
- **Coordinates:** 47.740749, -113.740341
## Injuries
- **Highest injury:** SERS
- **Fatal:** 0
- **Serious:** 2
- **Minor:** 0
- **Uninjured:** 0
- **Total aboard:** 2
## Aircraft
- **Make:** Beech
- **Model:** H-35
- **Registration:** N7975D
- **FAR Part:** 091
- **Engines:** 1
- **Damage:** SUBS
## Conditions
- **Light:** DAYL
- **Weather:** VMC
## 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.

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*Source: [NTSB CAROL](https://data.ntsb.gov/carol-main-public/basic-search?source=ntsb&type=event&ntsb_number=SEA99FA138) · AI Analytics · CC0 1.0*