# NTSB FTW94LA124: Bell 206L-3, N937S, Englewood, CO, April 15, 1994

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: April 15, 1994, 16:10 local (22:10 UTC)
- Place: Englewood, CO
- Coordinates: 39.640811, -104.989974 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.6408&lon=-104.9900&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed, report December 7, 1994
- Report: Approved by Office Director
- NTSB case key (mKey): 19031
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW94LA124
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/19031/pdf
- Page: https://openairdocs.org/ntsb/FTW94LA124

## Probable cause

THE PILOT'S FAILURE TO MAINTAIN ROTOR RPM, HIS DELAYED FLARE, AND IMPROPER TOUCHDOWN. A FACTOR WAS A FAILURE OF THE FUEL CONTROL/GOVERNOR TO THE HIGH SIDE WHICH REQUIRED THE PILOT TO PERFORM A FULL AUTOROTATION.

## Sequence of events

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

- Loss of engine power, maneuvering
  - turboshaft engine,free turbine governor - failure,partial (contributing factor)
- Forced landing, descent - emergency
- Hard landing, landing
  - rotor rpm - not maintained, pilot in command (cause)
  - flare - delayed, pilot in command (cause)
  - touchdown - improper, pilot in command (cause)

## Analysis

WHILE CONDUCTING A TEST FLIGHT FOLLOWING INSTALLATION OF A FUEL CONTROL/GOVERNOR, THE ENGINE ACCELERATED TO MAXIMUM POWER AND COULD NOT BE CONTROLLED BY THE PILOT.  THE PILOT SECURED THE ENGINE AND CONDUCTED AN AUTOROTATION.  DURING TOUCHDOWN, THE MAIN ROTOR BLADES CONTACTED THE TAIL BOOM AND SEVERED THE TAIL ROTOR DRIVE SHAFT.  EXAMINATION OF THE FUEL CONTROL/GOVERNOR REVEALED A PIECE OF ABRASIVE PAPER IN THE RESET SHAFT HOUSING.  ACCORDING TO THE EXAMINATION REPORT, THIS WOULD CAUSE LOSS OF GOVERNOR CONTROL TO THE HIGH SIDE.

## Factual narrative

On April 15, 1994, at 1610 mountain daylight time, a Bell 206L-3 helicopter, N937S, sustained substantial damage while executing an autorotation following an engine malfunction.  The pilot and passenger were not injured.  Visual meteorological conditions prevailed and no flight plan was filed for this local test flight.

According to the pilot, control of the engine was lost during a test flight and the engine accelerated to maximum power.  The pilot secured the engine and performed an autorotative landing.  During the landing sequence, the main rotor came in contact with the tail pylon severing the tail rotor drive shaft.  The test flight was being conducted due to installation of a fuel control/governor and the passenger (additional crew) was the mechanic who performed the work.

The engine, fuel control, and engine governor were removed and sent to the manufacturer, Allied Signal, for further examination.  Under direction from local FAA personnel, a functional test and visual examination was conducted.  The examination and testing revealed no discrepancies. (The narrative portion of the Allied Signal report is attached.  For the full report, contact Allied Signal for report number ECD422-AR64.)

Following return of the parts to U. S. West, the aircraft owner, the fuel control and governor were sent to an independent testing laboratory.  The results of their examination are attached and provide information that a foreign substance, described as a piece of abrasive paper, was found in the reset shaft housing of the governor.  According to the report, under the operating conditions present at the time of the occurrence, if the reset rod sticks, fuel flow will increase.

## Aircraft

- Registration: N937S (not matched to a registry record)
- Reported make and model: BELL 206L-3
- Category: Helicopter
- Serial number: 51258
- Airframe hours: 2537
- Engines: ALLISON 250-C30P 650 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Part 91
- Registered owner: Mtn States Tele & Telegraph
- Airworthiness certificate: Standard, Normal
- Last inspection: Continuous airworthiness, April 5, 1994, 17 hours before
- Airport: APA, Centennial

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 44; commercial; airplane ratings: single-engine land; instrument ratings: airplane, helicopter; medical: class 2, valid medical--no waivers/lim.; seat: right; flight hours: 11,135 total, 4,445 in this make and model, 10,535 as pilot in command, 65 in the last 90 days, 15 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 330° at 8 knots
- Visibility: 50 statute miles
- Lowest ceiling: none
- Temperature: 66 °F, dew point 34 °F
- Altimeter: 30.00 inHg
- Observed at: APA

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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