# NTSB DEN92LA036: Enstrom TH-28, N8631E, Leadville, CO, February 29, 1992

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: February 29, 1992, 10:22 local (17:22 UTC)
- Place: Leadville, CO
- Coordinates: 39.240932, -106.289146 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.2409&lon=-106.2891&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report July 23, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 18198
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN92LA036
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18198/pdf
- Page: https://openairdocs.org/ntsb/DEN92LA036

## Probable cause

THE PILOT MISJUDGING THE DESCENT RATE AND CONSEQUENTLY DELAYING THE FLARE. A FACTOR WAS:  DOWNDRAFT.

## Sequence of events

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

- In flight collision with terrain/water, descent
  - weather condition - downdraft (contributing factor)
  - autorotation - intentional, pilot in command
  - emergency procedure - simulated, pilot in command
  - descent - misjudged, pilot in command (cause)
  - flare - delayed, pilot in command (cause)

## Analysis

THIS WAS ONE OF A SERIES OF EXPERIMENTAL TEST FLIGHTS LEADING TOWARDS FAA CERTIFICATION OF THE MODIFIED HELICOPTER. DATA POINTS FOR THE HEIGHT VELOCITY CURVE HAD BEEN COLLECTED AND THE PILOT WAS ATTEMPTING TO CONFIRM THEIR ACCURACY. AT 46 KNOTS AND 400 FEET AGL, THE PILOT MADE AN INTENTIONAL AUTOROTATION.  HE SAID THE SINK RATE WAS HIGHER THAN PREVIOUSLY NOTED, AND HEAVY ROTOR BLADE STALL MADE THE FLARE INEFFECTIVE. THE PILOT SAID A DOWNDRAFT MAY HAVE PRECIPITATED THE ACCIDENT.

## Aircraft

- Registration: [N8631E](https://openairdocs.org/deregistered/N8631E-1994-04-06), registration cancelled 1994-04-06, S/N 3003 (OpenAirDocs)
- Reported make and model: ENSTROM TH-28
- Registry model: [Enstrom Helicopter TH-28](https://openairdocs.org/model/enstrom-helicopter-th-28) (registry code 3300435) (OpenAirDocs)
- Category: Helicopter
- Serial number: 3003
- Airframe hours: 575
- Engines: ALLISON 250-C20W 420 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Part 91
- Operator: Enstrom Helicopter Corporation
- Registered owner: Enstrom Helicopter Corporation
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: 100 hour, January 20, 1992, 36 hours before
- Airport: LXV, Lake County, runway 34, 5,300 × 75 ft, asphalt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 46; airline transport, flight instructor, commercial; airplane ratings: multi-engine land, single-engine sea, single-engine land; instrument ratings: helicopter, airplane; medical: class 1, valid medical--no waivers/lim.; seat: right; flight hours: 6,479 total, 889 in this make and model, 5,383 as pilot in command, 97 in the last 90 days, 50 in the last 30 days

## Weather

- Conditions: Visual (VMC), Day
- Wind: 340° at 5 knots
- Visibility: 30 statute miles
- Lowest ceiling: none
- Temperature: 39 °F, dew point 21 °F
- Altimeter: 30.00 inHg

## 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 19920229017419A](https://openairdocs.org/incident/19920229017419A), Feb 29, 1992: Enstrm 280FX, Leadville, CO, Substantial damage. Unable to arrest high sink rate on autorotation test. Impacted ground. Main rotors chopped tailboom.

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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