# NTSB FTW94LA166: Bell 47G, N933B, Sulphur, OK, May 18, 1994

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: May 18, 1994, 18:30 local (23:30 UTC)
- Place: Sulphur, OK
- Coordinates: 34.500545, -96.96949 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=34.5005&lon=-96.9695&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report November 14, 1994
- Report: Approved by Office Director
- NTSB case key (mKey): 19061
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW94LA166
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/19061/pdf
- Page: https://openairdocs.org/ntsb/FTW94LA166

## Probable cause

THE LOSS OF ENGINE POWER DUE TO THE FAILURE OF AN ENGINE ACCESSORY OIL PUMP GEAR. A FACTOR WAS THE LACK OF SUITABLE TERRAIN FOR THE AUTOROTATION.

## Sequence of events

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

- Loss of engine power(total) - mech failure/malf, maneuvering - aerial application
  - accessory drive assy,drive gear - failure,total (cause)
- Forced landing, descent - emergency
- Hard landing, descent - emergency
  - autorotation - initiated, pilot in command
  - terrain condition - none suitable (contributing factor)
  - object - tree(s)

## Analysis

A TOTAL LOSS OF ENGINE POWER OCCURRED AT 50 FEET ABOVE THE GROUND DURING THE INITIAL PHASE OF A TURN-AROUND MANEUVER. TREES HINDERED THE PILOT'S COMPLETION OF THE AUTOROTATION. THE HELICOPTER BOUNCED DURING THE LANDING AND THE MAIN ROTOR BLADE FLEXED AND SEVERED THE TAILBOOM. AN EXAMINATION OF THE ENGINE BY THE OPERATOR REVEALED THE FAILURE OF AN ENGINE ACCESSORY OIL PUMP GEAR.

## Factual narrative

On May 18, 1994, at 1830 central daylight time, a Bell 47G, N933B, sustained substantial damage during a forced landing near Sulphur, Oklahoma.  The commercial pilot did not receive injuries.  Visual meteorological conditions prevailed for the local aerial application flight.

The pilot reported a total loss of engine power at 50 feet above the ground during the initial phase of a turn-around maneuver.  He further said that trees in the area and the height of the helicopter hindered his completion of a successful autorotation.  The helicopter bounced during the hard landing and the main rotor blade flexed and severed the tailboom.

During a telephone interview the operator reported the total loss of engine power was due to the failure of the oil pump drive gear in the accessory case.

## Aircraft

- Registration: [N933B](https://openairdocs.org/deregistered/N933B-2017-06-30), registration cancelled 2017-06-30, S/N 662 (OpenAirDocs)
- Reported make and model: BELL 47G
- Registry model: [Bell 47G](https://openairdocs.org/model/bell-47g) (registry code 1181002) (OpenAirDocs)
- Registry engine: [Franklin 6V4 series](https://openairdocs.org/engine/franklin-6v4-series) (registry code 27033, reciprocating) (OpenAirDocs)
- Category: Helicopter
- Serial number: 662
- Engines: FRANKLIN 6V-335-A 210 horsepower reciprocating
- Damage: Substantial damage
- Flight: Aerial application, Part 137
- Registered owner: B & S Flying Service, Inc.
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: Annual, May 5, 1994, 21 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 27; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; seat: right; flight hours: 1,618 total, 1,164 in this make and model, 1,488 as pilot in command

## Weather

- Conditions: Visual (VMC), Day
- Wind: 60° at 3 knots
- Visibility: 10 statute miles
- Lowest ceiling: none

## 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 19940518011819A](https://openairdocs.org/incident/19940518011819A), May 18, 1994: Bell 47G, Sulphur, OK, Substantial damage. Engine failed on spray run pullup. Unable full autoratation. Hard impact. Cut tailboom. Oil pump drive gear failed.

## Other investigations on N933B (1)

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.

- [NTSB OAK76DVM08](https://openairdocs.org/ntsb/OAK76DVM08), Aug 20, 1975: Bell 47G (N933B), King City, CA, substantial damage

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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