# NTSB SEA98LA006: Bell 47-G3B, N47AH, Winston, MT, October 19, 1997 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: October 18, 1997, 21:30 local (Oct 19, 1997, 03:30 UTC) - Place: Winston, MT - Coordinates: 46.529022, -111.769912 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=46.5290&lon=-111.7699&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report February 15, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 42728 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA98LA006 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/42728/pdf - Page: https://openairdocs.org/ntsb/SEA98LA006 ## Probable cause Fuel starvation due to fuel flow restriction from a failed carburetor automatic mixture control device. Factors include night light conditions for the forced landing. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power, cruise - fuel system,carburetor - flow restricted (cause) - fluid,fuel - starvation (cause) - Forced landing, descent - emergency - Hard landing, landing - flare/touchdown - light condition - night (contributing factor) ## Analysis Post accident inspection revealed a loose bellows housing on the MA-6AA carburetor's automatic mixture control. The bellows housing was found loose on the threaded tube, which was still locked to the seat, allowing the bellows to screw down onto the tube, thereby restricting the fuel delivery orifice. The seat and lock nut remained securely bolted to the float. The last recorded carburetor repair was on 7/22/93, with 817 hours since that repair. Records did not reflect the nature of that repair. According to the carburetor manufacturer's engineering drawings, the bellows is bonded to the threaded tube with a permanent type plastic resin. ## Factual narrative On October 18, 1997, approximately 2130 mountain daylight time, a Bell 47G-3B, N47AH, being operated and flown by a private pilot, sustained substantial damage during a hard landing following a forced landing near Winston, Montana. The pilot and passenger were uninjured. Visual meteorological bright night conditions existed and no flight plan had been filed. The flight, which was personal, was to have been operated under 14CFR91, and was returning from Townsend, Montana, en route back to Helena. The pilot reported to an FAA inspector that while climbing through 4,800 feet above ground, the helicopter yawed momentarily and then the engine abruptly ceased developing power. The pilot transitioned into an emergency autorotation and was unable to regain power during the descent. Just prior to landing, the pilot maneuvered to the right to avoid trees and touched down hard on downward sloping terrain. The left skid buckled and the main rotor struck the tail boom, separating the tail rotor and its associated drive and gear box. Post accident inspection revealed a loose bellows housing on the MA-6AA carburetor's automatic mixture control , marked with P/N 293-549. The bellows housing was found loose on the threaded tube, which was still locked to the seat, allowing the bellows to screw down onto the tube, thereby restricting the fuel delivery orifice. The seat and lock nut remained securely bolted to the float bowl ,however one of the screws was not properly safetied with the tab washer. The last recorded carburetor repair was on 7/22/93, with 817 hours since that repair. Records did not reflect the nature of that repair. According to the carburetor manufacturer's engineering drawings, the bellows is bonded to the threaded tube with a permanent type plastic resin. A check of FAA service difficulty reports found one instance of a failure of the bonding material. ## Aircraft - Registration: [N47AH](https://openairdocs.org/aircraft/N47AH), registered now, S/N 2645, built 1961 (OpenAirDocs) - Reported make and model: Bell 47-G3B - Registry model: [Bell 47G-3B](https://openairdocs.org/model/bell-47g-3b) (registry code 1181026) (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: 2645 - Engines: Lycoming TVO-435-A1A 220 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Dale E. Horne - Airworthiness certificate: Standard, Normal - Last inspection: Annual, September 30, 1997, 96 hours before - Departed: 8U8, TOWNSEND, MT - Destination: HLN, HELENA, MT ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 44; private; medical: class 3, valid medical--w/ waivers/lim; seat: left; flight hours: 147 total, 143 in this make and model, 93 as pilot in command, 52 in the last 90 days, 11 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night/dark - Wind: 310° at 7 knots - Visibility: 30 statute miles - Lowest ceiling: none - Temperature: 39 °F, dew point 36 °F - Altimeter: 30.00 inHg - Observed at: HLN ## 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 19971018047319A](https://openairdocs.org/incident/19971018047319A), Oct 18, 1997: Bell 47G3B, Winston, MT, Substantial damage. (-16) On October 18, 1997, at approximately 2130 MST, Bell helicopter N47AH, while on a routine flight, the pilot reported that the aircraft yawed slightly,… ## Other investigations on N47AH (2) 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 GAA17CA436](https://openairdocs.org/ntsb/GAA17CA436), Jul 24, 2017: Bell 47G 3B (N47AH), Toterville, IA, substantial damage. Probable cause: The pilot’s failure to maintain rotor rpm while maneuvering at low altitude with low airspeed and a tailwind. - [NTSB CHI08CA254](https://openairdocs.org/ntsb/CHI08CA254), Aug 14, 2008: Bell 47G-3B (N47AH), Kenyon, MN, substantial damage. Probable cause: The pilot's inadequate preflight planning which resulted in the helicopter settling with power. 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.