# NTSB ATL89DKG06: Bell UH-1B, N840MC, Plains, GA, September 29, 1989

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Final report
- Date: September 29, 1989, 16:40 local (20:40 UTC)
- Place: Plains, GA
- Coordinates: 32.069782, -84.219223 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=32.0698&lon=-84.2192&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 2 fatal
- Status: Completed, report June 30, 1992
- Report: Approved by Office Director
- NTSB case key (mKey): 7830
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ATL89DKG06
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/7830/pdf
- Page: https://openairdocs.org/ntsb/ATL89DKG06

## Probable cause

IMPROPER MODIFICATION OF THE HELICOPTER BY THE COMPANY/OPERATOR, AND FAILURE OF THE SPRAY BOOM, WHICH RESULTED IN MAST BUMPING, AND SUBSEQUENT FAILURE OF THE MAIN ROTOR ASSEMBLY.

## Sequence of events

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

- Airframe/component/system failure/malfunction, cruise
  - aerial application equipment - improper (cause)
  - maintenance,modification - improper, company/operator management (cause)
  - aerial application equipment - failure,total (cause)
  - rotor drive system,main rotor mast(drive shaft) - failure,total (cause)
- In flight collision with terrain/water, descent - uncontrolled

## Analysis

DURING A POSITIONING FLT, AN IN-FLIGHT BREAKUP OF THE HELICOPTER OCCURRED IN THE VICINITY OF WHERE IT WAS CROSSING A LINE OF TREES BETWEEN 2 CLEARED AREAS.  WRECKAGE WAS FOUND SCATTERED OVER AN AREA OF APRX 300 YDS IN LENGTH, ALONG A HEADING OF 340 DEG.  AT THE SE END, PIECES WERE FOUND FROM THE LEFT SPRAY BOOM & MAIN ROTOR AERODYNAMIC FAIRING. FURTHER TO THE NW, VARIOUS PARTS WERE FOUND FROM THE LEFT SIDE OF THE HELICOPTER, LEFT SPRAY BOOM & TAIL ROTOR.  THE MAIN ROTOR & MAIN ROTOR HUB WERE FOUND ABOUT 120 YDS TO THE RIGHT OF THE WRECKAGE PATH.  THE FUSELAGE, ENG & TRANS- MISSION WERE FOUND ABOUT 240 YDS NW OF THE 1ST PART OF THE WRECKAGE.  AN EXAM OF THE WRECKAGE REVEALED THE MAIN ROTOR SYSTEM HAD SEPARATED DUE TO MAST BUMPING.  THERE WAS EVIDENCE THE LEFT SPRAY BOOM HAD CONTACTED THE MAIN ROTOR BLADES DURING FLT. ALL OF THE FRACTURES OF THE SPRAY BOOM, STEEL TRUSS & ASSOC LUGS INDCD OVERLOAD FAILURE IN AFT & UPWARD DRCTN.  THE SPRAY ASSEMBLY & BOOM HAD NOT BEEN INSTALLED IN ACCORDANCE WITH FAR PART 23.

## Aircraft

- Registration: [N840MC](https://openairdocs.org/deregistered/N840MC-1991-08-22), registration cancelled 1991-08-22, S/N 603619 (OpenAirDocs)
- Reported make and model: BELL UH-1B
- Registry model: [Bell UH-1B](https://openairdocs.org/model/bell-uh-1b) (registry code 1181410) (OpenAirDocs)
- Category: Helicopter
- Serial number: 60-3619
- Airframe hours: 4921
- Engines: LYCOMING T53-11D 1100 horsepower turbo shaft
- Damage: Destroyed
- Flight: Positioning, Part 137
- Registered owner: Agrotors, Inc.
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: 100 hour, September 20, 1989, 4 hours before
- Departed: PLAINS, GA
- Destination: 82A, BUENA VISTA, GA

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 28; commercial, flight instructor; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; seat: right; toxicology performed; flight hours: 4,165 total, 1,351 in this make and model, 4,024 as pilot in command, 122 in the last 90 days, 58 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 7 statute miles
- Lowest ceiling: 1,300 ft overcast
- Temperature: 79 °F, dew point 72 °F

## 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 19890929037199A](https://openairdocs.org/incident/19890929037199A), Sep 29, 1989: Bell UH1B, Plains, GA, Destroyed, 2 fatal. Helicopter came apart inflight. Found evidence of mast bumping which failed main rotors.

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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