# NTSB DEN86LA040: Helio H-391B, N4101D, Bozeman, MT, December 6, 1985

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: December 6, 1985, 14:34 local (21:34 UTC)
- Place: Bozeman, MT
- Coordinates: 45.769138, -110.929779 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=45.7691&lon=-110.9298&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed
- Report: Approved by Office Director
- NTSB case key (mKey): 16893
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN86LA040
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/16893/pdf
- Page: https://openairdocs.org/ntsb/DEN86LA040

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Loss of engine power(total) - mech failure/malf, cruise
  - electrical system,electric wiring - burned (contributing factor)
  - maintenance,annual inspection - inadequate, other maintenance personnel (contributing factor)
  - electrical system,electric wiring - shorted (contributing factor)
  - ignition system,magneto - failure,total (cause)
- Forced landing, descent - emergency
- In flight collision with terrain/water, landing
  - terrain condition - snow covered

## Analysis

ACCORDING TO PERSONNEL IN THE AREA, THE PLT RADIOED HE HAD SMOKE IN THE COCKPIT AND WAS RETURNING TO GALLANTIN FIELD, HIS DEPARTURE POINT. LATER, THE PLT TRANSMITTED THAT THE ENG LOST TOTAL PWR AND HE WAS MAKING A FORCED LANDING. DURING THE INVESTIGATION, IT WAS ASCERTAINED THE WIRING BETWEEN THE INSTRUMENT PANEL AND THE MAGNETOS HAD BURNED EXTENSIVELY AND THE MAGNETO 'P' LEAD HAD SHORTED OUT.

## Aircraft

- Registration: [N4101D](https://openairdocs.org/deregistered/N4101D-2013-03-07), registration cancelled 2013-03-07, S/N 016, built 1955 (OpenAirDocs)
- Reported make and model: HELIO H-391B
- Registry model: [Helio H-391B](https://openairdocs.org/model/helio-h-391b) (registry code 4300106) (OpenAirDocs)
- Registry engine: [Lycoming GO-435C&D series](https://openairdocs.org/engine/lycoming-go-435c-d-series) (registry code 41521, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: 016
- Airframe hours: 583
- Engines: LYCOMING GO-435 reciprocating
- Damage: Substantial damage
- Fire: In-Flight
- Flight: Personal, Part 91
- Registered owner: Boyne Mountain Lodge, Inc.
- Airworthiness certificate: Standard, Normal; Standard, Utility
- Last inspection: 100 hour, December 6, 1985
- Departed: BZN, BOZEMAN, MT
- Destination: PORTLAND, OR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 48; private; airplane ratings: single-engine land, single-engine sea; medical: class 3, valid medical--w/ waivers/lim; seat: left; flight hours: 3,200 total, 42 in this make and model

## Weather

- Conditions: Visual (VMC), Day
- Wind: 132° at 3 knots
- Visibility: 34 statute miles
- Lowest ceiling: 25,000 ft broken
- Temperature: 25 °F
- Altimeter: 30.00 inHg
- Observed at: BZN, 2 nm away

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19851206061059A](https://openairdocs.org/incident/19851206061059A), Dec 6, 1985: Helio H391B, Bozeman, MT, Substantial damage. Magnetos grounded, p lead insulation worn, shorted out. Should have turned off master switch when smelled smoke.

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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