# NTSB FTW91LA154: Bell L4 Experimental, N2770X, Arlington, TX, August 24, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: August 24, 1991, 07:59 local (12:59 UTC)
- Place: Arlington, TX
- Coordinates: 32.760662, -97.140357 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=32.7607&lon=-97.1404&mi=10
- Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed, report March 31, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 23392
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW91LA154
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/23392/pdf
- Page: https://openairdocs.org/ntsb/FTW91LA154

## Probable cause

THE PILOT'S FAILURE TO MAINTAIN ADEQUATE ROTOR RPM DURING THE PLANNED AUTOROTATION AND HIS IMPROPER TOUCHDOWN.

## Sequence of events

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

- Hard landing, landing - flare/touchdown
  - autorotation - initiated, pilot in command
  - rotor rpm - not maintained, pilot in command (cause)
  - touchdown - improper, pilot in command (cause)
  - misc rotorcraft,tail boom - separation

## Analysis

THE FLIGHT TEST PILOT WAS CONDUCTING HEIGHT/VELOCITY MANEUVERS ON THE MANUFACTURERS NEW HELICOPTER. A PLANNED AUTOROTATION WAS INITIATED TO THE RUNWAY. A HARD LANDING OCCURRED, AND A MAIN ROTORBLADE CONTACTED THE TAILBOOM, SEVERING IT. AN EYEWITNESS STATED THE HELICOPTER TOUCHED DOWN ON THE REAR SKIDS AND BOUNCED SEVERAL TIMES BEFORE THE TAILBOOM SEPARATED. NO MECHANICAL FAILURE WAS REPORTED BY THE PILOT.

## Aircraft

- Registration: N2770X (not matched to a registry record)
- Reported make and model: BELL L4 EXPERIMENTAL (L4 EXPERIM)
- Category: Helicopter
- Serial number: 51022
- Airframe hours: 3541
- Engines: ALLISON 250C30P 650 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Other work use, Part 91
- Operator: Bell Helicopter Textron, Inc.
- Registered owner: Bell Helicopter Textron, Inc.
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: Unknown, January 2, 2000
- Departed: 0
- Flight plan: Company VFR
- Airport: F54, Arlington, runway 34, 4,000 × 100 ft, asphalt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 44; commercial, airline transport, flight instructor; airplane ratings: multi-engine land, single-engine land; instrument ratings: helicopter, airplane; medical: class 2, valid medical--no waivers/lim.; seat: right; flight hours: 11,400 total, 2,138 in this make and model, 8,513 as pilot in command

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 75 °F, dew point 70 °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 19910824036669A](https://openairdocs.org/incident/19910824036669A), Aug 24, 1991: Bell 206L, Arlington, TX, Substantial damage. Impacted runway during test flight autorotation. Was performing high velocity maneuver in avoid area of envelope.

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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