# NTSB DEN88FA063: Cessna 421A, N517S, Helena, MT, February 4, 1988

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Field investigation · Final report
- Date: February 3, 1988, 20:00 local (Feb 4, 1988, 03:00 UTC)
- Place: Helena, MT
- Coordinates: 46.530223, -112.209693 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=46.5302&lon=-112.2097&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 3 fatal
- Status: Completed, report January 16, 1990
- Report: Approved by Office Director
- NTSB case key (mKey): 17351
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN88FA063
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/17351/pdf
- Page: https://openairdocs.org/ntsb/DEN88FA063

## Sequence of events

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

- In flight collision with terrain/water, approach - iaf to faf/outer marker (ifr)
  - terrain condition - mountainous/hilly
  - light condition - dark night (contributing factor)
  - ifr procedure - improper, pilot in command (cause)
  - navigation receiver - improper use of, pilot in command (cause)

## Analysis

THIS ACCIDENT OCCURRED DURING A NIGHT, ILS APP TO RWY 27 IN IMC. THE ACFT COLLIDED WITH A MOUNTAIN 12 NM ESE OF THE ARPT WHILE TURNING INBOUND TO INTERCEPT THE LOC COURSE. INVESTIGATION REVEALED THAT ONE VOR RECEIVER WAS SET ON THE DESTINATON ILS FREQ, THE SECOND VOR WAS SET ON AN EN ROUTE VOR 51 NM WEST OF THE DESTINATION ARPT, AND THE DME RADIO, A SEPARATE TRANSCEIVER, WAS SET ON THE DESTINATION DME TRANSMITTER. THE FREQS OF THE EN ROUTE VOR AND THE DESTINATION VOR WERE 117.1 AND 117.7, RESPECTIVELY. THE OUTBOUND COURSE FOR THE ILS APP PROCEDURE WAS 088 DEG AND THE ACDT SITE WAS LOCATED ON THE 088 RADIAL OF THE EN ROUTE VOR. INVESTIGATION ALSO REVEALED THAT THE PIC WAS OCCUPYING THE RT FRONT SEAT AND AN EXPERIENCED PLT WHO WAS NOT CURRENT IN THIS AIRCRAFT WAS OCCUPYING THE LEFT SEAT. THE SECOND VOR RECEIVER CONTROL HEAD WAS LOCATED IN THE LOWER RIGHT PORTION OF THE INST PANEL, IN A LOCATION WHERE THE SELECTED FREQ WAS DIFFICULT TO READ.

## Aircraft

- Registration: [N517S](https://openairdocs.org/deregistered/N517S-1991-04-01), registration cancelled 1991-04-01, S/N 421A0002 (OpenAirDocs)
- Reported make and model: CESSNA 421A
- Registry model: [Cessna 421A](https://openairdocs.org/model/cessna-421a) (registry code 2076012) (OpenAirDocs)
- Category: Airplane
- Serial number: 421A002
- Airframe hours: 4758
- Engines: CONTINENTAL GTSIO-520-D 375 horsepower reciprocating
- Damage: Destroyed
- Fire: On-Ground
- Flight: Part 135
- Operator: Minuteman Aviation
- Registered owner: Kenneth Mamuzich
- Airworthiness certificate: Standard, Normal
- Last inspection: 100 hour, December 8, 1987, 22 hours before
- Departed: MSO, MISSOULA, MT
- Destination: HLN, HELENA, MT
- Flight plan: IFR
- Airport: HLN, Helena Regional, runway 27, 9,000 × 150 ft, asphalt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 54; airline transport; airplane ratings: single-engine land, multi-engine land, single-engine sea, multi-engine sea; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; seat: right; toxicology performed; flight hours: 4,900 total, 119 in this make and model, 4,503 as pilot in command, 35 in the last 90 days, 35 in the last 30 days, 4 in the last 24 hours

## Weather

- Conditions: Instrument (IMC), Night/dark
- Temperature: 27 °F, dew point 19 °F
- Altimeter: 30.00 inHg
- Observed at: HLN, 12 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 19880203002029A](https://openairdocs.org/incident/19880203002029A), Feb 3, 1988: Cessna 421A, Helena, MT, Destroyed, 3 fatal. Struck trees on mountainside on ILS approach at night in heavy snow. Co pilot at controls left seat. Acft burned.

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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