# NTSB LAX97TA213: Bell 47G-3B-1, N1335X, Fallon, NV, June 16, 1997 - Type: NTSB accident investigation - Classification: Accident · No injuries · Final report - Date: June 16, 1997, 12:28 local (19:28 UTC) - Place: Fallon, NV - Coordinates: 39.499603, -118.289726 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.4996&lon=-118.2897&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed, report May 21, 1998 - Report: Approved by Office Director - NTSB case key (mKey): 29912 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX97TA213 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/29912/pdf - Page: https://openairdocs.org/ntsb/LAX97TA213 ## Probable cause exhaustion of the aircraft's fuel supply, due to improper planning and/or decision. A factor related to the accident was the high density altitude which made a successful autorotative landing unlikely. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - nonmechanical, maneuvering - planning/decision - inadequate, pilot in command (cause) - fluid,fuel - exhaustion (cause) - Forced landing, emergency descent/landing - autorotation - initiated - Hard landing, emergency landing - weather condition - high density altitude (contributing factor) ## Analysis The engine of the helicopter lost power after about 3 hours of flying. An autorotative descent was made to a site at 6,500 feet density altitude, and the helicopter was damaged during the landing. After the accident, 1.9 gallons of fuel were drained from the entire fuel system. The helicopter's unusable fuel quantity was 2.5 gallons. Examination of the helicopter revealed no evidence of a preaccident mechanical malfunction or failure. A manufacturer's representative opined that an autorotative landing at 6,500 feet density altitude would likely result in a hard landing. The engine carburetor flow tested within the manufacturer's specifications. ## Factual narrative On June 16, 1997, at 1228 hours Pacific daylight time, a Bell 47G-3B-1 helicopter, N1335X, lost engine power while returning to a refueling site and was substantially damaged during the ensuing forced landing at Fallon, Nevada. The commercial pilot and two passengers were not injured. Visual meteorological conditions prevailed. The aircraft was operated by High Desert Helicopters as a public-use aircraft under contract to the U.S. Department of the Interior and was engaged in a census of wild horses. An investigator from the Department of the Interior, Office of Aircraft Services (OAS), examined the wreckage and drained 1.9 gallons of fuel from the entire fuel system. The aircraft has a 2.5 gallon unusable fuel quantity. The OAS examination of the aircraft found no evidence of mechanical malfunction or failure. The pilot's load calculation form shows that the aircraft departed with 60 gallons of fuel, however, the aircraft flight manual states that the maximum fuel load is 57 usable gallons and that when the fuel gage indicates EMPTY the fuel remaining is not usable in flight. According to the OAS investigator, the engine hour meter recorded that the engine lost power after 3.0 hours of flight. The owner/pilot acknowledged exhausting the aircraft's fuel supply to the OAS investigator, but felt that the aircraft should have had more endurance. He reported that the engine should have consumed 18 gallons per hour and the endurance should have been 3.5 hours. He felt that the higher fuel consumption was due to a faulty carburetor. He did not report any error or abnormality in the fuel quantity gage. The engine carburetor was sent to the manufacturer by the OAS for a flow test examination on July 26, 1997. It flow tested within the manufacturer's specifications. The carburetor was not disassembled for examination by the manufacturer. In October, 1997, the operator returned the carburetor for examination by the company which last overhauled it. A representative of that company identified an air leak past the inner throttle shaft seal below the butterfly. The inspector advanced a theory that leakage past the seal could have resulted in a false reference pressure signal to the automatic mixture control which might have caused the engine fuel mixture to become abnormally rich. He reported that the damage to the seal might have resulted from a blow on the end of the throttle shaft sometime after the carburetor was overhauled. The inspector also advanced a theory why the enriched mixture would only occur in a supercharged pressure environment and would not have been detected in the flow bench test at atmospheric pressure. Their report is attached. The density altitude was approximately 6,500 feet. A representative of the aircraft manufacturer told the Safety Board that an autorotative landing at that density altitude would likely result in a "hard landing," and that there is no information in the aircraft flight manual to tell the pilot at what density altitude an autorotative landing without damage becomes unlikely. ## Aircraft - Registration: [N1335X](https://openairdocs.org/aircraft/N1335X), registered now, S/N 6556, built 1966 (OpenAirDocs) - Reported make and model: Bell 47G-3B-1 - Registry model: [Bell 47G-3B-1](https://openairdocs.org/model/bell-47g-3b-1) (registry code 1181028) (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: 6556 - Airframe hours: 10151 - Engines: Lycoming TVO-435-B1A 270 horsepower reciprocating - Damage: Substantial damage - Flight: Public aircraft, Part 91 - Operator: U.S. Dept. Of The Interior - Registered owner: Clifford J. Heaverne - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, May 20, 1997, 10 hours before - Departed: FLX, NV - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 53; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: helicopter, airplane; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 23,926 total, 10,112 in this make and model, 22,902 as pilot in command, 46 in the last 90 days, 13 in the last 30 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: variable at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 84 °F, dew point 48 °F - Altimeter: 30.00 inHg - Observed at: NFZ, 53 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 19970616014299A](https://openairdocs.org/incident/19970616014299A), Jun 16, 1997: Bell 47G3B1, Fallon, NV, Substantial damage. Experienced engine failure while returning to base. ## Other investigations on N1335X (4) 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 FTW96TA383](https://openairdocs.org/ntsb/FTW96TA383), Sep 10, 1996: Bell 47G-3B-1 (N1335X), Rangely, CO, substantial damage. Probable cause: the pilot's excessive cyclic control input during a low altitude operation, and his failure to maintain altitude/clearance from high vegetation (sage brush). The proximity of high vegetation was a… - [NTSB LAX79DX030](https://openairdocs.org/ntsb/LAX79DX030), Jul 14, 1979: Bell 47G3B1 (N1335X), Montello, NV, substantial damage - [NTSB CAN70A4457](https://openairdocs.org/ntsb/CAN70A4457), Jul 26, 1969: Bell 47G3B1 (N1335X), Hope, Canada, destroyed, 3 fatal - [NTSB OAK69F0318](https://openairdocs.org/ntsb/OAK69F0318), May 11, 1969: Bell 47G3B1 (N1335X), Las Vegas, NV, 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. --- 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.