# NTSB ATL91FA013: Bell 47J-2, N49DA, Gatlinburg, TN, November 1, 1990

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Field investigation · Final report
- Date: November 1, 1990, 14:00 local (19:00 UTC)
- Place: Gatlinburg, TN
- Coordinates: 35.7201, -83.490249 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=35.7201&lon=-83.4902&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 1 serious, 2 minor
- Status: Completed, report December 14, 1992
- Report: Approved by Office Director
- NTSB case key (mKey): 8296
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ATL91FA013
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/8296/pdf
- Page: https://openairdocs.org/ntsb/ATL91FA013

## Probable cause

THE ACCIDENT WAS INADEQUATE MAINTENANCE OF THE HELICOPTER, ALLOWING A TAIL ROTOR DRIVE SHAFT BEARING TO EXCEED WEAR LIMITS. THIS RESULTED IN HIGH LOADS ON THE TAIL ROTOR DRIVE SHAFT, AND THE RESULTING FATIGUE FAILURE OF THE DRIVE SHAFT.

## Sequence of events

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

- Airframe/component/system failure/malfunction, cruise - normal
  - rotor drive system,tail rotor drive shaft bearing - worn (cause)
  - rotor drive system,tail rotor drive shaft - fatigue (cause)
  - maintenance,inspection - inadequate, company maintenance personnel (cause)
  - misc eqpt/furnishings,seat belt - improper
- Loss of control - in flight, cruise - normal
- In flight collision with object, descent - uncontrolled
  - object - tree(s)
- In flight collision with terrain/water, descent - uncontrolled

## Analysis

THE TWO PASSENGERS REPORTED THAT THEY HEARD A 'POP' SOUND, FOLLOWED BY THE HELICOPTER STARTING A CLOCKWISE SPIN TO THE RIGHT. THE HELICOPTER DESCENDED INTO THE TREES ON THE SIDE OF A STEEP SLOPE. INVESTIGATION REVEALED THAT THE TAIL ROTOR DRIVE SHAFT FAILED IMMEDIATELY FORWARD OF THE TAILBOOM EXTENSION TUBE. THE DRIVE SHAFT FAILED FROM FATIGUE CRACKING, PROPAGATING AT A HIGH RATE, SUGGESTING HIGH LOADS. THE T/R DRIVE SHAFT FORWARD BEARING HOUSING OUTER DIAMETER DIMENSION AND THE INNER DIAMETER OF THE TAILBOOM EXTENSION TUBE WERE WORN BEYOND REPLACEMENT LIMITS AND SHOULD HAVE BEEN REPLACED ACCORDING TO THE BELL MAINTENANCE AND OVERHAUL MANUAL. THE PASSENGER THREE-PLACE BENCH SEAT HAD BEEN ALTERED SO THAT THE INDIVIDUAL SEAT BELTS HAD BEEN MODIFIED INTO ONE SINGLE LONG BELT. THE BELT COULD BE OPENED ONLY ON THE LEFT SIDE OF THE BELT; THE BUCKLE ON THE RIGHT SIDE OF THE BELT WAS TAPED CLOSED WITH SILVER DUCT TAPE.

## Aircraft

- Registration: [N49DA](https://openairdocs.org/deregistered/N49DA-2014-11-26), registration cancelled 2014-11-26, S/N 1825, built 1960 (OpenAirDocs)
- Reported make and model: BELL 47J-2
- Registry model: [Bell 47J-2](https://openairdocs.org/model/bell-47j-2) (registry code 1181104) (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: 1825
- Airframe hours: 8972
- Engines: LYCOMING VO-540-B1B3 260 horsepower reciprocating
- Damage: Destroyed
- Flight: Part 91
- Operator: Pigeon Forge Helicopters, Inc.
- Registered owner: Pigeon Forge Helicopters, Inc
- Last inspection: Annual, October 7, 1990, 85 hours before
- Departed: NONE, PIGEON FORGE, TN

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 43; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: front; toxicology performed; flight hours: 8,448 total, 8,370 as pilot in command, 385 in the last 90 days, 120 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 15 statute miles
- Lowest ceiling: none
- Temperature: 73 °F, dew point 43 °F
- Altimeter: 30.00 inHg
- Observed at: TYS, 26 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 19901101048849A](https://openairdocs.org/incident/19901101048849A), Nov 1, 1990: Bell 47J2, Gatlinburg, TN, Destroyed. Tail rotor drive shaft failed due to drive shaft housing and bearings worn beyond minimums. Spiraled into trees.

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.

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.