# NTSB ANC13LA063: Curtiss Wright C-46F, N1837M, Fairbanks, AK, July 3, 2013 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 2, 2013, 16:00 local (Jul 3, 2013, 00:00 UTC) - Place: Fairbanks, AK - Coordinates: 64.808891, -147.853881 - Nearby events: https://openairdocs.org/map.md?lat=64.8089&lon=-147.8539&mi=10 - Phase of flight: [Taxi](https://openairdocs.org/ntsb-phases/250) (OpenAirDocs' grouping) - Defining event: [Taxi-from runway: Comm system malf/failure](https://openairdocs.org/ntsb-events/336) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report June 2, 2014 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - Parties: Federal Aviation Administration - NTSB case key (mKey): 87452 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC13LA063 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/87452/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=87452 - Page: https://openairdocs.org/ntsb/ANC13LA063 ## Probable cause The failure of the right main landing gear side brace due to fatigue, which resulted in a collapse of the right main landing gear. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: main landing gear attach sec](https://openairdocs.org/ntsb-findings/01023211): Aircraft › Aircraft systems · Fatigue/wear/corrosion (probable cause); cases with it: [Curtiss Wright C-46F, 1 case](https://openairdocs.org/ntsb-findings/01023211/cases.md?model=2622608), [All aircraft, 66 cases](https://openairdocs.org/ntsb-findings/01023211/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Taxi-from runway: Comm system malf/failure](https://openairdocs.org/ntsb-events/336) (defining event); cases with it: [Curtiss Wright C-46F, 1 case](https://openairdocs.org/ntsb-events/336/sequence.md?model=2622608), [All aircraft, 20 cases](https://openairdocs.org/ntsb-events/336/sequence.md) - [Taxi-from runway: Landing gear collapse](https://openairdocs.org/ntsb-events/094); cases with it: [Curtiss Wright C-46F, 1 case](https://openairdocs.org/ntsb-events/094/sequence.md?model=2622608), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) ## Analysis During the maintenance test flight, the flight crew moved the landing gear handle to the "down" position but did not observe the three green landing gear down-and-locked lights illuminate. After cycling the landing gear "several" times they observed a gear down-and-locked indication in the cockpit. After landing, while taxiing to parking, the right main landing gear collapsed, and the right wing and aileron struck the ground and sustained substantial damage. The right landing gear side brace fractured near the fuselage attach forging due to fatigue, which initiated near the weld between the large end fuselage attach forging and the outer tube. No obvious discontinuities such as porosity or undercutting were visually noted in the weld adjacent to the fracture. ## Factual narrative On July 2, 2013, about 1600 Alaska daylight time, a twin-engine Curtiss Wright, C-46F airplane, N1837M, sustained substantial damage while taxiing to parking at the Fairbanks International Airport, Fairbanks, Alaska. The commercial certificated captain and the airline transport certificated first officer were not injured. The airplane was registered to and operated by Evert's Air Fuel, under the provisions of Title 14 Code of Federal regulations Part 91, as a visual flight rules (VFR) maintenance test flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The operator reported that during the maintenance test flight, the flight crew moved the landing gear handle to the "down" position, but did not observe the three green landing gear down-and-lock lights illuminate. After cycling the landing gear "several" times they observed a gear down-and-locked indication in the cockpit. After landing, while taxiing to parking, the right main landing gear collapsed, and the right wing and aileron sustained substantial damage. A postaccident examination, of the landing gear system revealed that both inner and outer tubes of the right landing gear side brace, separated near the fuselage attach forging. The fractured main landing gear side brace assembly was sent to the NTSB's Materials Laboratory in Washington, D.C. for examination. A senior Safety Board metallurgist reported that a magnified optical examination of the landing gear side brace assembly fracture surfaces revealed ratchet marks, arrest lines, and flat fracture regions consistent with fatigue propagation. No obvious discontinuities such as porosity or undercutting were visually noted in the weld adjacent to the fracture. A complete copy of the NTSB's materials laboratory factual report is included in the public docket for this accident. In the recommendation section of the NTSB Accident/Incident Reporting Form 6120.1, the operator stated that the accident may have been prevented if the flight crew would have shut down the airplane clear of the runway, and had the landing gear inspected before taxiing to parking. They also noted, that three green down-and-lock lights illuminated is the normal indication for a positive lock. ## Aircraft - Registration: [N1837M](https://openairdocs.org/aircraft/N1837M), registered now, S/N 22388, built 1944 (OpenAirDocs) - Reported make and model: CURTISS WRIGHT C-46F - Registry model: [Curtiss Wright C-46F](https://openairdocs.org/model/curtiss-wright-c-46f) (registry code 2622608) (OpenAirDocs) - Registry engine: [Pratt & Whitney R-2800 series](https://openairdocs.org/engine/pratt-whitney-r-2800-series) (registry code 52026, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 22388 - Airframe hours: 35183 - Engines: P & W R-2800 SERIES 2000 horsepower reciprocating; P & W R-2800 SERIES 2000 horsepower reciprocating - Damage: Substantial damage - Flight: Flight test, Part 91 - Operator: Everts Air Fuel Inc - Registered owner: Everts Air Fuel Inc - Airworthiness certificate: Standard, Transport - Last inspection: AAIP, July 1, 2013 - Departed: PAFA, Fairbanks, AK - Destination: PAFA, Fairbanks, AK - Airport: PAFA, Fairbanks International Airpor, runway 20R, 11,800 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 55; injuries: none; flight engineer, commercial; airplane ratings: single-engine land, multi-engine land, single-engine sea; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review April 29, 2013; seat: left; flight hours: 20,100 total, 3,000 in this make and model, 20,000 as pilot in command - Co-pilot; age 38; injuries: none; airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, with waivers/limitations; last flight review May 6, 2013; seat: right; flight hours: 2,100 total, 95 in this make and model, 1,700 as pilot in command, 130 in the last 90 days, 25 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 250° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: 7,000 ft broken - Temperature: 72 °F, dew point 39 °F - Altimeter: 29.60 inHg - Observed at: PAFA ## 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 20130702015419A](https://openairdocs.org/incident/20130702015419A), Jul 2, 2013: Curtiss Wright C-46F, Fairbanks, AK, Substantial damage. Aircrew noted no downlock indication lights after gear extension in prep for landing. Cycled gear a few times after initial extension failure when green down… ## Docket (2 files) The files NTSB released with the investigation on March 14, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=87452. 711 KB in all. - Materials Laboratory 15 - Factual Report 13-099 (w 4 images) (item 1, .PDF, 315 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40405314&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Factual%20Report%2013-099%20(w%204%20images)-Master.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 2, .PDF, 396 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40407807&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.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.