# NTSB CHI92LA137: Bell 47-G2A, N52HB, Dousman, WI, April 30, 1992

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Limited investigation · Final report
- Date: April 30, 1992, 10:45 local (15:45 UTC)
- Place: Dousman, WI
- Coordinates: 43.010726, -88.469551 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=43.0107&lon=-88.4696&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 1 serious, 1 minor
- Status: Completed, report July 29, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 15435
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI92LA137
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/15435/pdf
- Page: https://openairdocs.org/ntsb/CHI92LA137

## Probable cause

THE IN-FLIGHT LOSS OF THE SWASH PLATE DRIVE LINK BOLT WHICH ALLOWED THE SWASH PLATE DRIVE ASSEMBLY TO DISCONNECT.

## Sequence of events

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

- Airframe/component/system failure/malfunction, cruise - normal
  - rotorcraft flight control,swashplate assembly - disconnected (cause)
- Forced landing, descent - emergency
- In flight collision with object, landing - flare/touchdown
  - object - tree(s) (contributing factor)
- In flight collision with terrain/water, descent - uncontrolled
  - terrain condition - high vegetation

## Analysis

THE FLIGHT INSTRUCTOR (CFI) REPORTED THE DUAL INSTRUCTIONAL FLIGHT PROCEEDED WITHOUT INCIDENT FOR THE FIRST HOUR. WHILE RETURNING TO THE AIRPORT IN CRUISE FLIGHT, A SUDDEN AND VERY VIOLENT VIBRATION OCCURRED. THE CFI TOOK THE FLIGHT CONTROLS AND BEGAN AN AUTOROTATION TO AN OFF-AIRPORT SITE, STRIKING TREES DURING THE DESCENT. INSPECTION OF THE ROTOR HEAD DISCOVERED A MISSING SWASH PLATE DRIVE LINK BOLT, WHICH ALLOWED THE DRIVE LINK TO DISCONNECT. BOTH THE CFI AND STUDENT RECALLED CHECKING THE BOLT AND ASSOCIATED NUT AND COTTER PIN PRIOR TO THE FLIGHT AND FOUND NO ANOMALIES. THE BOLT WAS NEVER LOCATED.

## Aircraft

- Registration: [N52HB](https://openairdocs.org/deregistered/N52HB-2018-03-06), registration cancelled 2018-03-06, S/N 3244, built 1964 (OpenAirDocs)
- Reported make and model: BELL 47-G2A
- Registry model: [Bell 47G-2A](https://openairdocs.org/model/bell-47g-2a) (registry code 1181012) (OpenAirDocs)
- Registry engine: [Lycoming VO-435 series](https://openairdocs.org/engine/lycoming-vo-435-series) (registry code 41525, reciprocating) (OpenAirDocs)
- Category: Helicopter
- Serial number: 3244
- Airframe hours: 8600
- Engines: LYCOMING VO-435-A1F 240 horsepower reciprocating
- Damage: Substantial damage
- Flight: Instructional, Part 91
- Operator: Mc Dermott Enterprises, Inc., doing business as Ideal Helicopter Service
- Registered owner: Mc Dermott Enterprises, Inc.
- Airworthiness certificate: Standard, Normal
- Last inspection: 100 hour, February 7, 1992, 94 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 51; flight instructor, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: helicopter, airplane; medical: class 2, valid medical--w/ waivers/lim; seat: right; flight hours: 17,000 total, 5,000 in this make and model

## Weather

- Conditions: Visual (VMC), Day
- Wind: 50° at 10 knots
- Visibility: 8 statute miles
- Lowest ceiling: none
- Temperature: 55 °F
- Altimeter: 30.00 inHg
- Observed at: UES, 10 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 19920430012239A](https://openairdocs.org/incident/19920430012239A), Apr 30, 1992: Bell 47G2A, Dousman, WI, Substantial damage. Severe vibration autorotated to a tree lined clearing. Struck trees. Bolt was missing from swarsh plate drive cover

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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