# NTSB SEA91LA077: Bell BH-47G2A, N38926, Waitsburg, WA, March 31, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: March 31, 1991, 08:15 local (16:15 UTC)
- Place: Waitsburg, WA
- Coordinates: 46.219707, -118.14907 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=46.2197&lon=-118.1491&mi=10
- Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report May 5, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 41405
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA91LA077
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41405/pdf
- Page: https://openairdocs.org/ntsb/SEA91LA077

## Probable cause

THE IMPROPER INSTALLATION OF THE MAIN ROTOR MAST NUT AND LOCK WASHER BY MAINTENANCE PERSONNEL WHICH RESULTED IN THE SEPARATION OF THE MAIN ROTOR SYSTEM.

## Sequence of events

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

- Airframe/component/system failure/malfunction, landing
  - rotor system,tail rotor hub retaining nut - separation (cause)
  - maintenance,installation - improper, company maintenance personnel (cause)

## Analysis

WHILE THE PILOT WAS LOWERING THE COLLECTIVE PITCH AFTER LANDING TOUCHDOWN, THE MAIN ROTOR SEPARATED FROMT HE MAST.  THE EXAMINATION REVEALED THE IMPROPER INSTALLATION OF THE MAST NUT AND LOCK WASHER WHEN THE MAIN ROTOR WAS INSTALLED.

## Aircraft

- Registration: [N38926](https://openairdocs.org/deregistered/N38926-2012-11-14), registration cancelled 2012-11-14, S/N N.A.H.1957-1, built 1973 (OpenAirDocs)
- Reported make and model: BELL BH-47G2A
- Registry model: [Bell 47G-2](https://openairdocs.org/model/bell-47g-2) (registry code 1181008) (OpenAirDocs)
- Registry engine: [Lycoming VO-435 series](https://openairdocs.org/engine/lycoming-vo-435-series) (registry code 41525, reciprocating) (OpenAirDocs)
- Category: Helicopter
- Serial number: NAH 1957-1
- Engines: LYCOMING VO-435A1F 260 horsepower reciprocating
- Damage: Substantial damage
- Flight: Aerial application, Part 137
- Operator: Waitsburg Helicopter Service
- Registered owner: Waitsburg Helicopter Service

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 45; commercial; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 8,000 total, 8,000 in this make and model, 8,000 as pilot in command, 150 in the last 90 days, 40 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 340° at 5 knots
- Visibility: 50 statute miles
- Lowest ceiling: none
- Temperature: 46 °F, dew point 39 °F
- Altimeter: 30.00 inHg
- Observed at: PSC, 37 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 19910331007939A](https://openairdocs.org/incident/19910331007939A), Mar 31, 1991: Bell 47G2, Waitsburg, WA, Substantial damage. Main rotor separated from mast just after touchdown. Lock washers not properly installed on recent maintenance.

## Other investigations on N38926 (5)

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 SEA05LA138](https://openairdocs.org/ntsb/SEA05LA138), Jul 5, 2005: Bell 47G-2A (N38926), Oroville, WA, substantial damage. Probable cause: The failure of the throttle cable housing, which permitted the engine's RPM to decay to the idle position. Contributing factors were the trees and the lack of suitable terrain for a forced landing.
- [NTSB FTW77FPG86](https://openairdocs.org/ntsb/FTW77FPG86), Sep 19, 1977: Bell 47G2H1 (N38926), Mountain View, AR, destroyed
- [NTSB FTW76DRG70](https://openairdocs.org/ntsb/FTW76DRG70), Jul 17, 1976: Bell 47G-2 (N38926), Mcallen, TX, substantial damage
- [NTSB FTW75DPG68](https://openairdocs.org/ntsb/FTW75DPG68), May 26, 1975: Bell 47G-2 (N38926), Denmark, AR, substantial damage
- [NTSB MKC73AK059](https://openairdocs.org/ntsb/MKC73AK059), Apr 6, 1973: Bell 47G-2 (N38926), Owatonna, MN, 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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