# NTSB DEN91FA065: Piper PA-31B-310, N7407L, Bennett, CO, May 1, 1991

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Field investigation · Final report
- Date: May 1, 1991, 06:53 local (12:53 UTC)
- Place: Bennett, CO
- Coordinates: 39.739822, -104.780685 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.7398&lon=-104.7807&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 1 fatal
- Status: Completed, report October 2, 1992
- Report: Approved by Office Director
- NTSB case key (mKey): 18020
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN91FA065
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18020/pdf
- Page: https://openairdocs.org/ntsb/DEN91FA065

## Probable cause

IN-FLIGHT SEPARATION OF THE LEFT ENGINE COWL ASSEMBLY THAT WAS NOT PROPERLY LATCHED, AND FAILURE OF THE PILOT TO MAINTAIN MINIMUM CONTROL SPEED, WHICH RESULTED IN HIS LOSS OF AIRCRAFT CONTROL.  FACTORS RELATED TO THE ACCIDENT WERE: AN INADEQUATE PREFLIGHT INSPECTION, INADEQUATE MARKINGS/ALIGNMENT INDICATIONS TO ASSURE THAT THE COWL FASTENERS WERE LOCKED, AND AN INSUFFICIENTLY DEFINED PROCEDURE IN THE FLIGHT MANUAL FOR CHECKING THE COWL FASTENERS.

## Sequence of events

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

- Airframe/component/system failure/malfunction, climb - to cruise
  - cooling system,cowling - unlatched (cause)
  - aircraft preflight - inadequate (contributing factor)
  - aircraft/equipment inadequate, manufacturer (contributing factor)
  - acft/equip,inadequate aircraft manuals, manufacturer (contributing factor)
  - condition(s)/step(s) insufficiently defined, manufacturer (contributing factor)
  - cooling system,cowling - separation (cause)
  - vertical stabilizer surface - bent
- Loss of engine power, climb
  - 1 engine - switched off
  - propeller feathering - not attained, pilot in command
- Forced landing, descent - emergency
- Loss of control - in flight, descent - uncontrolled
  - airspeed(vmc) - not maintained, pilot in command (cause)
  - aircraft control - not maintained, pilot in command (cause)
- In flight collision with terrain/water, descent - uncontrolled

## Analysis

SHORTLY AFTER TAKEOFF, WHILE CLIMBING TO CRUISE ALTITUDE, THE PILOT REPORTED THE LEFT ENGINE COWL ASSEMBLY HAD COME OFF. WITNESSES OBSERVED THE AIRPLANE AT LOW ALTITUDE & NOTED THAT IT WAS 'YAWING, SPUTTERING, AND ROCKING BACK AND FORTH.'  THEY INDICATED THE LEFT ENGINE WAS NOT RUNNING & THAT THE AIRPLANE BANKED SHARPLY TO THE RIGHT & DISAPPEARED BEHIND TREES BEFORE CRASHING. AN INVESTIGATION REVEALED THE LEFT PROPELLER HAD NOT BEEN FEATHERED. THE LEFT ENGINE COWLING WAS FOUND 1.8 MILES FROM THE ACCIDENT SITE. THE THREE PRIMARY (EYEBOLT) COWL FASTERERS ON THE OUTBOARD SIDE OF THE LEFT UPPER COWL WERE FOUND UNLOCKED & SEVEN OTHER COWL ATTACHING STUDS (SCREWS) WERE MISSING. THE COWLING HAD BEEN REMOVED 16 DAYS BEFORE THE ACCIDENT TO INSTALL AN OIL/AIR SEPARATOR. THIS WAS THE FIRST FLIGHT SINCE THAT WORK WAS PERFORMED. THE MECHANIC, WHO DID THE WORK, SAID HE NOTED SEVERAL COWL STUD FASTENERS WERE MISSING & THAT HE HAD NOTIFIED THE PILOT. THE PILOT WAS REPORTED TO HAVE REPLIED THAT HE HAD SOME FASTENERS & WOULD TAKE CARE OF THE PROBLEM.

## Aircraft

- Registration: [N7407L](https://openairdocs.org/deregistered/N7407L-2014-11-17), registration cancelled 2014-11-17, S/N 31-790, built 1971 (OpenAirDocs)
- Reported make and model: PIPER PA-31B-310
- Registry model: [Piper PA-31-310](https://openairdocs.org/model/piper-pa-31-310) (registry code 7103102) (OpenAirDocs)
- Registry engine: [Lycoming TI0-540 series](https://openairdocs.org/engine/lycoming-ti0-540-series) (registry code 41533, turbo-prop) (OpenAirDocs)
- Category: Airplane
- Serial number: 31-790
- Engines: LYCOMING TIO-540-A2B 310 horsepower reciprocating
- Damage: Destroyed
- Fire: On-Ground
- Flight: Business, Part 91
- Operator: John Westbrook, doing business as John Westbrook, Inc.
- Departed: APA, ENGLEWOOD, CO
- Destination: DSM, DES MOINES, IA

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 45; private; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 3, valid medical--no waivers/lim.; toxicology performed; flight hours: 6,200 total, 6,094 as pilot in command, 150 in the last 90 days

## Weather

- Conditions: Visual (VMC), Day
- Wind: 150° at 3 knots
- Visibility: 50 statute miles
- Lowest ceiling: none
- Temperature: -0 °F, dew point -0 °F
- Observed at: APA, 21 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 19910501013939A](https://openairdocs.org/incident/19910501013939A), May 1, 1991: Piper PA31310, Bennett, CO, Destroyed, 1 fatal. Lost left engine cowl and power. Not feathered. Below VMC lost control. Left turbo failed. Failed to secure cowl.

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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