# NTSB ERA20LA216: Bell 47G, N473TT, Atoka, TN, June 15, 2020 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: June 14, 2020, 20:30 local (Jun 15, 2020, 01:30 UTC) - Place: Atoka, TN - Coordinates: 35.413333, -89.653053 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.4133&lon=-89.6531&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Eastern Region Aviation - Parties: FAA FSDO - NTSB case key (mKey): 101438 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA20LA216 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/101438/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=101438 - Page: https://openairdocs.org/ntsb/ERA20LA216 ## Probable cause A total loss of engine power due to a blocked fuel line; the reason for the blockage could not be determined based on the available evidence. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [Bell 47G-3B-1, 3 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=1181028), [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md) - [Engine fuel and control](https://openairdocs.org/ntsb-findings/01057300): Aircraft › Aircraft power plant · Malfunction (probable cause); cases with it: [Bell 47G-3B-1, 1 case](https://openairdocs.org/ntsb-findings/01057300/cases.md?model=1181028), [All aircraft, 49 cases](https://openairdocs.org/ntsb-findings/01057300/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Bell 47G-3B-1, 5 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=1181028), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Autorotation: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Bell 47G-3B-1, 3 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=1181028), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) ## Analysis The pilot had conducted eight brief (7- to 8-minute) nonrevenue passenger flights uneventfully on the day of the accident. The helicopter was fueled before the eighth flight. During the ninth flight, the helicopter’s engine lost total power when the helicopter was about 1.5 miles north of the heliport and was descending through an altitude of 900 ft mean sea level. The pilot executed an autorotation and landed in a field. On touchdown, the main rotor blade struck the tailboom. Postaccident examination of the airframe and engine revealed no evidence of any preimpact malfunctions except for the fuel line to the carburetor, which had collapsed. A borsescope inspection revealed that light could not be observed through the fuel line. The borescope was then pushed through the fuel line, and no contaminates were found. A subsequent metallurgical examination of the fuel line revealed no blockages; no damage to the interior of the hose; and no evidence of kinks, creases, or material creep. The blocked fuel line likely resulted in the loss of engine power; however, the reason for the blockage could not be determined. ## Factual narrative On June 14, 2020, about 2030 central daylight time, a Bell 47G, N473TT, was substantially damaged when it was involved in an accident near Burnett Heliport (59TN), Atoka, Tennessee. The pilot and two passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, on the day of the accident, he was providing short (7- to 8-minute) nonrevenue passenger flights. The pilot had completed eight flights uneventfully. The pilot had added 20 gallons of fuel (10 gallons to each tank) to the helicopter before the eighth flight, for a total of about 39 gallons. During the ninth flight, when the helicopter was about 1.5 miles north of 59TN and was descending through 900 ft mean sea level, the engine lost all power. The pilot performed an autorotation to a field; during touchdown, the main rotor blade struck the tailboom, which severed the aft 20 inches of the tailboom, including the tail rotor, from the airframe. Postaccident examination of the accident site revealed that the helicopter came to rest upright in the field. All major components of the helicopter were found. The engine showed no evidence of a preimpact malfunction, and all components were present. The hydraulic pump was removed for access to the drive so that the crankshaft could be turned. One spark plug was removed in each cylinder for a compression check, and the crankshaft was rotated using a tool inserted in the pump drive pad. Continuity of the crankshaft, camshaft, and valve train was confirmed. A borescope inspection of the cylinders found no anomalies. Both magnetos rotated normally, and the timing was within normal limits. All ignition leads and spark plugs appeared to be completely functional. The air filter and induction system inspection indicated no obstruction to air flow. The throttle had a normal operating range. The fuel line to the carburetor appeared to have collapsed, and about 4 ounces of fuel drained from the system after disconnecting the line. The fuel line was inspected using a borescope, and no light passed through the fuel line. The borescope was then pushed through the fuel line, and no contaminates were found. Both the left and right fuel tanks tested normal for 100LL fuel with no contamination. The fuel sample obtained from the fuel supply system on the support truck was determined to be uncontaminated. The fuel line was subsequently examined by the National Transportation Safety Board’s Materials Laboratory. No blockages were observed; the interior of the hose appeared undamaged and intact; and no evidence of kinks, creases, or material creep was observed on the exterior of the fuel line. ## Aircraft - Registration: [N473TT](https://openairdocs.org/aircraft/N473TT), registered now, S/N 3730, built 1968 (OpenAirDocs) - Reported make and model: Bell 47G (3B1) - 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: 3730 - Year built: 1968 - Airframe hours: 10125 - Engines: Lycoming V0-435-A1F 260 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: A&F Aviation Services Llc - Registered owner: A&F Aviation Services Llc - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, May 23, 2020, 8 hours before - Airport: 59TN, Burnett - Equipment: ADS-B ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 64; injuries: none; airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: helicopter, airplane; medical: class 2, with waivers/limitations; last flight review June 30, 2019; seat: left; restraint: 3-point; flight hours: 11,145 total, 1,220 in this make and model, 10,950 as pilot in command, 30 in the last 90 days, 20 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Dusk - Wind: 50° at 4 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 82 °F, dew point 66 °F - Altimeter: 30.12 inHg - Observed at: NQA, 11 nm away ## Docket (6 files) The files NTSB released with the investigation on September 22, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=101438. 6.7 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 3.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13232751&FileExtension=pdf&FileName=NTSB%20Report%20N473TT%20%20%20%20%20%20%20%20%20%20%20%20%20%206-17-2020_Redacted-Rel.pdf - Pilot statement (item 2, PDF, 4 pages, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13847628&FileExtension=pdf&FileName=Pilot%20Statement_Redacted-Rel.pdf - Engine examination (item 3, PDF, 2 pages, 194 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13578287&FileExtension=pdf&FileName=Engine%20Examination_Redacted-Rel.pdf - Materials laboratory factual report (item 4, PDF, 2 pages, 309 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13847028&FileExtension=pdf&FileName=Fuel%20Line%20Exam_Redacted-Rel.pdf - Investigative photographs (item 5, PDF, 4 pages, 727 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13233160&FileExtension=pdf&FileName=Investigative%20Photographs%20-%20ERA20LA216-Rel.pdf - Wreckage release (item 6, PDF, 1 page, 607 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13843201&FileExtension=pdf&FileName=NTSB%20release%20form_Redacted-Rel.pdf 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.