# NTSB CHI91LA257: Bell 47G, N61SD, Lake Ozark, MO, August 11, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: August 10, 1991, 20:05 local (Aug 11, 1991, 01:05 UTC)
- Place: Lake Ozark, MO
- Coordinates: 38.179832, -92.619132 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=38.1798&lon=-92.6191&mi=10
- Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report March 9, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 15153
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI91LA257
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/15153/pdf
- Page: https://openairdocs.org/ntsb/CHI91LA257

## Probable cause

FAILURE OF THE ROTORCRAFT'S TAIL BOOM IN FLIGHT.  FACTORS RELATED TO THE ACCIDENT WERE REDUCED AIRCRAFT CONTROL AVAILABLE TO THE PILOT.

## Sequence of events

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

- Airframe/component/system failure/malfunction, takeoff - initial climb
  - misc rotorcraft,tail boom - failure,total (cause)
  - autorotation - performed, pilot in command
  - aircraft control - reduced, pilot in command (contributing factor)
- Forced landing, descent - emergency
- Hard landing, descent - emergency
  - terrain condition - water

## Analysis

THE PILOT SAID THAT SHORTLY AFTER TAKEOFF HE HEARD A LOUD SNAP, FOLLOWED BY AN UNCOMMANDED RIGHT YAW.  AN EMERGENCY AUTOROTATION WAS EXECUTED WHICH RESULTED IN A HARD WATER LANDING.  POST ACCIDENT INVESTIGATION REVEALED THE CHROMEMOLY TUBING HAD FAILED IN FRONT OF THE TAIL ROTOR YOKE, IN FLIGHT.

## Aircraft

- Registration: [N61SD](https://openairdocs.org/aircraft/N61SD), registered now, S/N 3551, built 1966 (OpenAirDocs)
- Reported make and model: BELL 47G
- Registry model: [Bell 47G-3B-1](https://openairdocs.org/model/bell-47g-3b-1) (registry code 1181028) (OpenAirDocs)
- Registry engine: [Lycoming TVO-435-GIA](https://openairdocs.org/engine/lycoming-tvo-435-gia) (registry code 41526, turbo-prop) (OpenAirDocs)
- Category: Helicopter
- Serial number: 3551
- Airframe hours: 9065
- Engines: LYCOMING VO-435-AIF 260 horsepower reciprocating
- Damage: Substantial damage
- Flight: Business, Part 91
- Operator: Central Wisconsin Helicopters
- Airworthiness certificate: Standard, Normal
- Last inspection: Continuous airworthiness, August 2, 1991, 15 hours before
- Departed: BAGNELL DAM, MO

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 29; flight instructor, commercial; airplane ratings: single-engine land; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 1,017 total, 227 in this make and model, 698 as pilot in command, 159 in the last 90 days, 57 in the last 30 days, 7 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 40° at 3 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Observed at: AIZ, 1 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 19910810033099A](https://openairdocs.org/incident/19910810033099A), Aug 10, 1991: Bell 47G3B2, Osage Beach, MO, Substantial damage. Lost tail rotor control. Yawed. Autorotated to hard water landing. Tailboom broke off due failure chrome tubing.

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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