# NTSB ANC12TA035: Piper PA-18-150, N7059, Paxon, AK, April 28, 2012 - Type: NTSB accident investigation - Classification: Accident · No injuries · Final report - Date: April 27, 2012, 16:20 local (Apr 28, 2012, 00:20 UTC) - Place: Paxon, AK - Coordinates: 61.210491, -149.890518 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=61.2105&lon=-149.8905&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing-landing roll: Landing gear collapse](https://openairdocs.org/ntsb-events/094) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report February 27, 2013 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - Parties: FAA FSDO-03 - NTSB case key (mKey): 83510 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC12TA035 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/83510/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=83510 - Page: https://openairdocs.org/ntsb/ANC12TA035 ## Probable cause A separation of the right main landing gear suspension strut assembly due to overstress, which resulted in the collapse of the main landing gear while landing. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: main gear strut/axle/truck](https://openairdocs.org/ntsb-findings/01023213): Aircraft › Aircraft systems · Failure (probable cause); cases with it: [Piper PA-18-150, 2 cases](https://openairdocs.org/ntsb-findings/01023213/cases.md?model=7101828), [All aircraft, 86 cases](https://openairdocs.org/ntsb-findings/01023213/cases.md) - [Runway/land/takeoff/taxi surface: snow/slush/ice covered surface](https://openairdocs.org/ntsb-findings/03023015): Environmental issues › Physical environment · Contributed to outcome; cases with it: [Piper PA-18-150, 7 cases](https://openairdocs.org/ntsb-findings/03023015/cases.md?model=7101828), [All aircraft, 219 cases](https://openairdocs.org/ntsb-findings/03023015/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330); cases with it: [Piper PA-18-150, 4 cases](https://openairdocs.org/ntsb-events/330/sequence.md?model=7101828), [All aircraft, 996 cases](https://openairdocs.org/ntsb-events/330/sequence.md) - [Landing-landing roll: Landing gear collapse](https://openairdocs.org/ntsb-events/094) (defining event); cases with it: [Piper PA-18-150, 16 cases](https://openairdocs.org/ntsb-events/094/sequence.md?model=7101828), [All aircraft, 1,789 cases](https://openairdocs.org/ntsb-events/094/sequence.md) ## Analysis The pilot said he was landing a ski-equipped airplane on a remote, frozen and snow-covered lake. He said that as the skis contacted the flat and smooth snow-covered ice, the airplane pitched forward violently, then to the right, and then back to the left. A postaccident examination revealed that the right main landing gear had collapsed and subsequently folded under the airplane. An examination of the right main landing gear revealed a fractured suspension strut that had fractured laterally across a bored and threaded area of the suspension tube. The fractured tube was examined under magnification and there was no evidence of external corrosion. The tube had a long radius bend adjacent to the internal threads. The fracture had a clean, evenly colored fracture surface, and no evidence of repeated fracturing (beach marking). The fracture appearance is consistent with an overstress fracture. The pilot noted that, other than the fractured main landing suspension strut, there were no preaccident mechanical anomalies with the airplane. ## Factual narrative On April 27, 2012, about 1620 Alaska daylight time, a ski-equipped Piper PA-18-150 airplane, N7059, sustained substantial damage when the right main landing gear collapsed while landing on a frozen, snow-covered lake, about 28 miles west of Paxon, Alaska. The airplane was operated by the State of Alaska Department of Public Safety, Alaska State Troopers, Anchorage, Alaska, as a visual flight rules (VFR) public use flight under the provisions of Title 14 Code of Federal Regulations Part 91, when the accident occurred. The solo pilot was not injured, and company flight following procedures were in effect, for the flight that departed Anchorage about 1400. In a written statement to the National Transportation Safety Board investigator-in-charge dated April 30, the pilot reported that while on a routine law enforcement flight he landed on a remote, frozen and snow-covered lake. He said that as the skis contacted the flat and smooth snow-covered ice, the airplane pitched forward violently, then to the right, and then back to the left. The pilot’s postaccident examination revealed that the right main landing gear had collapsed, and subsequently folded under the airplane. The airplane sustained substantial damage to the wings and the fuselage. The airplane was equipped with a Burl’s Aircraft LLC, Alpha Omega Suspension System (AOSS), which was installed in accordance with supplemental type certificate (STC) SA02214AK. A postaccident examination of the right main landing gear revealed a fractured suspension strut that had fractured laterally across a bored and threaded suspension tube. The tube had a slight bend with tearing along the fracture line on the inside of the bend. The pilot reported that other than the fractured main landing suspension strut, there were no preaccident mechanical anomalies with the airplane. ## Aircraft - Registration: [N7059](https://openairdocs.org/aircraft/N7059), registered now, S/N 18-8043, built 1963 (OpenAirDocs) - Reported make and model: PIPER PA-18-150 - Registry model: [Piper PA-18-150](https://openairdocs.org/model/piper-pa-18-150) (registry code 7101828) (OpenAirDocs) - Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 18-8043 - Airframe hours: 11575 - Engines: LYCOMING O-320 SERIES 160 horsepower reciprocating - Damage: Substantial damage - Flight: Public aircraft - state, Public use - Operator: State Of Alaska Department Of Public Safety - Registered owner: State Of Alaska Department Of Public Safety - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, February 24, 2012 - Departed: LHD, Anchorage, AK - Destination: Paxon, AK - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 55; injuries: none; private; airplane ratings: single-engine sea, single-engine land; medical: class 2, without waivers/limitations; last flight review August 26, 2010; seat: front; flight hours: 2,400 total, 2,400 in this make and model, 2,400 as pilot in command, 60 in the last 90 days, 40 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 100 statute miles - Lowest ceiling: none - Temperature: 55 °F ## 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 20120427007929A](https://openairdocs.org/incident/20120427007929A), Apr 27, 2012: Piper PA-18-150, Paxon, AK, Substantial damage. The pilot stated he attempted a landing at an undisclosed location. The pilot reported the landing was aborted due to excessive roughness. The pilot then flew… ## Other investigations on N7059 (1) 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 ANC00TA075](https://openairdocs.org/ntsb/ANC00TA075), Jun 23, 2000: Piper PA-18 (N7059), Quinhagak, AK, substantial damage. Probable cause: The pilot's inadequate compensation for wind conditions during takeoff. Factors associated with the accident were the sudden windshift from a crosswind to a tailwind. ## Docket (3 files) The files NTSB released with the investigation on January 9, 2013, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=83510. 3.5 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 2.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40380547&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Supplemental Type Certificate (item 2, .PDF, 355 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40380551&FileExtension=.PDF&FileName=Supplemental%20Type%20Certificate-Redacted.PDF - FAA Form 337 (item 3, .PDF, 228 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40380550&FileExtension=.PDF&FileName=FAA%20Form%20337-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.