# NTSB SEA93LA055: Boeing A75N1, N56924, Medicine Bow, WY, January 20, 1993

- Type: NTSB accident investigation
- Classification: Accident · Minor injuries · Limited investigation · Final report
- Date: January 19, 1993, 18:10 local (Jan 20, 1993, 01:10 UTC)
- Place: Medicine Bow, WY
- Coordinates: 41.889579, -106.199516 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=41.8896&lon=-106.1995&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Minor injuries
- Injuries: 1 minor
- Status: Completed, report October 13, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 42978
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA93LA055
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/42978/pdf
- Page: https://openairdocs.org/ntsb/SEA93LA055

## Probable cause

FAILURE OF THE #7 CYLINDER ROCKER ARM. FACTORS CONTRIBUTING TO THE ACCIDENT WERE UNSUITABLE TERRAIN AND DARK NIGHT CONDITIONS.

## 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
  - engine assembly,rocker arm/tappet - failure,total (cause)
- Forced landing, descent - emergency
- In flight collision with terrain/water, landing
  - light condition - dark night (contributing factor)
  - terrain condition - none suitable (contributing factor)

## Analysis

THE PILOT REPORTED THAT SHORTLY AFTER LEVELLING OFF AT 14,000 FEET MSL, THE ENGINE SURGED THREE TIMES AND THEN STOPPED. A FORCED LANDING WAS EXECUTED ONTO ROCKY, UPSLOPING TERRAIN, UNDER DARK NIGHT CONDITIONS. SUBSEQUENT DISASSEMBLY OF THE ENGINE REVEALED THAT THE NUMBER 7 CYLINDER INTAKE VALVE ROCKER ARM HAD FAILED.

## Aircraft

- Registration: N56924 (not matched to a registry record)
- Reported make and model: BOEING A75N1
- Category: Airplane
- Serial number: 75-2480
- Airframe hours: 6601
- Engines: P&W R-985-AN1 450 horsepower reciprocating
- Damage: Substantial damage
- Flight: Personal, Part 91
- Operator: Denton, Larry E.
- Registered owner: Denton, Larry E.
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: Annual, January 2, 1993, 10 hours before
- Departed: RKS, ROCK SPRINGS, WY
- Destination: LAR, LARAMIE, WY

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 57; flight instructor, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--w/ waivers/lim; seat: rear; flight hours: 9,999 total, 9,999 in this make and model, 9,999 as pilot in command, 40 in the last 90 days, 5 in the last 24 hours

## Weather

- Conditions: Night/dark
- Wind: 250° at 14 knots
- Visibility: 7 statute miles
- Lowest ceiling: 1,500 ft overcast
- Temperature: 25 °F, dew point 21 °F
- Altimeter: 29.00 inHg
- Observed at: RWL, 43 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 19930119002529A](https://openairdocs.org/incident/19930119002529A), Jan 19, 1993: Boeing A75N1, Medicine Bow, WY, Substantial damage. Unable to reach destination due to weather. Reversed course to return to rwl. Engine quit. Cause not given.

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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