# NTSB MKC85FA100: Bell 47G, N951B, Calwood, MO, May 9, 1985

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Field investigation · Final report
- Date: May 9, 1985, 13:30 local (18:30 UTC)
- Place: Calwood, MO
- Coordinates: 38.880577, -91.760543 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=38.8806&lon=-91.7605&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 2 fatal
- Status: Completed
- Report: Approved by Office Director
- NTSB case key (mKey): 33834
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=MKC85FA100
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/33834/pdf
- Page: https://openairdocs.org/ntsb/MKC85FA100

## 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 system,tail rotor hub - fatigue (cause)
  - tail rotor/anti-torque control - improper, manufacturer (cause)
  - inadequate quality control, manufacturer (cause)
- Loss of control - in flight, cruise - normal
- In flight collision with object, descent - uncontrolled
  - object - tree(s)

## Analysis

N951B CRASHED IN A WOODED AREA DURING A POWERLINE PATROL FLT WHICH INCLUDED PHOTOGRAPHY OF THE POWERLINE. ACCORDING TO WITNESSES, THE HELICOPTER WAS FLYING PARALLEL TO THE POWERLINE IN A WESTERLY DIRECTION WHEN THE ACCIDENT OCCURRED. EXAM OF THE WRECKAGE REVEALED THE TAIL ROTOR GEAR BOX AND HUB, ALONG WITH ON TAIL ROTOR BLADE HAD SEPARATED IN FLT AND WAS LOCATED APRX 50 YARDS FROM THE MAIN WRECKAGE. THE OTHER TAIL ROTOR BLADE WAS LOCATED APRX 160 YARDS AWAY FROM THE MAIN WRECKAGE. METALLURGICAL EXAM OF THE BROKEN YOKE REVEALED A FATIGUE FRACTURE WHICH PROGRESSED FROM MULTIPLE ORIGINS AT THE ROOT OF THE INTERNAL THREADS OF THE SPLINE. THE EXAM ALSO SHOWED THAT THE INTERNAL THREADS WERE NITRIDE TREATED. THIS WAS NOT A BELL HELICOPTER PART. THE PMA, UNDER WHICH THIS PART WAS MANUFACTURED, PROHIBITS NITRIDE TREATMENT OF THE SPINDLE BORE & THREADS.

## Aircraft

- Registration: N951B (not matched to a registry record)
- Reported make and model: BELL 47G
- Category: Helicopter
- Serial number: 695
- Airframe hours: 9280
- Engines: FRANKLIN 6V-335-A 200 horsepower reciprocating
- Damage: Destroyed
- Fire: On-Ground
- Flight: Aerial observation, Part 91
- Registered owner: Dick Hill Helicopters, Inc.
- Airworthiness certificate: Standard, Normal
- Last inspection: 100 hour, April 15, 1985, 48 hours before
- Departed: COU, COLUMBIA, MO

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 24; commercial, flight instructor; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 210 total, 210 in this make and model, 155 as pilot in command, 130 in the last 90 days, 4 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 230° at 13 knots
- Visibility: 20 statute miles
- Lowest ceiling: none
- Temperature: 75 °F, dew point 50 °F
- Altimeter: 30.00 inHg
- Observed at: COU, 21 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 19850509016269A](https://openairdocs.org/incident/19850509016269A), May 9, 1985: Bell 47G, Calwood, MO, Destroyed, 1 fatal. Tail rotor yoke spindle fatigue cracked, failed. Nitriding of spindle bore threads unauthorized. Hit trees, burned.

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.