# NTSB FTW93LA272: Coen Benson B8, Aurora, CO, September 3, 1993

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Limited investigation · Final report
- Date: September 3, 1993, 16:27 local (23:27 UTC)
- Place: Aurora, CO
- Coordinates: 39.629699, -104.779823 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.6297&lon=-104.7798&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 1 fatal
- Status: Completed, report August 1, 1994
- Report: Approved by Office Director
- NTSB case key (mKey): 18841
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW93LA272
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18841/pdf
- Page: https://openairdocs.org/ntsb/FTW93LA272

## Probable cause

FATIGUE FAILURE OF THE CENTER ENGINE MOUNT THAT ALTERED THE THRUST AND LIFT VECTORS.

## Sequence of events

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

- Loss of control - in flight, cruise - normal
  - engine assembly,mount - failure,total (cause)
  - engine assembly,mount - fatigue
  - aircraft control - not possible, pilot in command
- In flight collision with terrain/water, descent - uncontrolled
  - terrain condition - open field

## Analysis

THE AIRCRAFT WAS SEEN FLYING BETWEEN 300 AND 400 FEET ABOVE THE GROUND WHEN, ACCORDING TO A WITNESS, IT SUDDENLY 'ROLLED RIGHT, NEARLY INVERTED, AND DESCENDED APPROXIMATELY 80 DEGREES NOSE DOWN.' SEVERAL DEEP GOUGES AND A SCRAPE MARK WERE NOTED ATOP THE ENGINE CRANKCASE, DIRECTLY BENEATH THE CENTER ENGINE MOUNTING BOLT. THE ENGINE MOUNT WAS FRACTURED. THIS FRACTURE, ACCORDING TO A METALLURGIST, WAS DUE TO FATIGUE. THE REMAINING FRACTURES WERE DUE TO OVERLOAD. THERE WAS NO EVIDENCE OF FLIGHT CONTROL MALFUNCTION OR FAILURE.

## Factual narrative

On September 3, 1993, approximately 1627 mountain daylight time, an unregistered Coen's Benson B8 impacted terrain in Aurora, Colorado.  The pilot was fatally injured and the aircraft was destroyed.  Visual meteorological conditions prevailed at the time, and no flight plan was filed for the personal flight.

A motorist saw the gyroplane flying at an altitude between 300 and 400 feet.  He said the aircraft suddenly "rolled right, nearly inverted, and descended at approximately 80 degrees nose down."  A Federal Aviation Administration inspector who went to the accident site reported all components of the aircraft were recovered, and noted the main rotor blades were bowed "conically."

Examination of the wreckage revealed several deep gouges and a scrape mark atop the engine crankcase, directly beneath the center engine mounting bolt.  The engine mount was fractured.  According to a University of Denver metallurgist, it appeared this fracture was due to fatigue.  The remaining fractures were the result of overload.  No evidence of flight control malfunction or failure was found.

## Aircraft

- Registration: UNREG (not matched to a registry record)
- Reported make and model: COEN BENSON B8
- Category: Gyroplane, amateur-built
- Engines: MCCULLOCH 4318 90 horsepower reciprocating
- Damage: Destroyed
- Flight: Personal, Part 91
- Registered owner: Coen, Gary D.
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: Unknown, September 3, 1993
- Departed: FTG, WATKINS, CO

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 57; student; medical: class 3, expired; seat: front; toxicology performed; flight hours: 90 total

## Weather

- Conditions: Visual (VMC), Day
- Visibility: 50 statute miles
- Lowest ceiling: none

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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