# NTSB WPR17LA056: Beech 99, N326CA, Billings, MT, January 19, 2017 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: January 19, 2017, 11:48 local (18:48 UTC) - Place: Billings, MT - Coordinates: 45.807777, -108.542778 - Nearby events: https://openairdocs.org/map.md?lat=45.8078&lon=-108.5428&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report April 13, 2020 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 94631 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17LA056 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/94631/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=94631 - Page: https://openairdocs.org/ntsb/WPR17LA056 ## Probable cause The fatigue failure of the left main landing gear (MLG) actuator piston rod, which prevented the hydraulic system from producing pressure to control the MLG’s position and led to the right MLG collapsing during landing. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: landing gear actuator](https://openairdocs.org/ntsb-findings/01023233): Aircraft › Aircraft systems · Failure (probable cause); cases with it: [Beech 99A, 1 case](https://openairdocs.org/ntsb-findings/01023233/cases.md?model=1154003), [All aircraft, 54 cases](https://openairdocs.org/ntsb-findings/01023233/cases.md) - [Landing gear system: landing gear actuator](https://openairdocs.org/ntsb-findings/01023233): Aircraft › Aircraft systems · Fatigue/wear/corrosion (probable cause); cases with it: [Beech 99A, 1 case](https://openairdocs.org/ntsb-findings/01023233/cases.md?model=1154003), [All aircraft, 54 cases](https://openairdocs.org/ntsb-findings/01023233/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Initial climb: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) (defining event); cases with it: [Beech 99A, 1 case](https://openairdocs.org/ntsb-events/330/sequence.md?model=1154003), [All aircraft, 994 cases](https://openairdocs.org/ntsb-events/330/sequence.md) - [Landing-landing roll: Landing gear collapse](https://openairdocs.org/ntsb-events/094); cases with it: [Beech 99A, 2 cases](https://openairdocs.org/ntsb-events/094/sequence.md?model=1154003), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) ## Analysis The commercial pilot reported that, after departing for the cross-country, cargo flight, he retracted the landing gear and heard a "thud" sound. Subsequently, the main landing gear (MLG) "unsafe" light illuminated, and the left MLG light remained illuminated green, indicating that it was still extended despite the landing gear handle being in the retracted position. The pilot returned to the departure airport, and during touchdown, the right MLG collapsed, which resulted in substantial damage to the right aileron and right wing spar. During the postaccident examination of the landing gear, the left MLG actuator's piston rod was found fractured. Metallurgical examination of the piston rod revealed that the rod had failed in its threaded section due to fatigue cracking over about 60% of the cross-section. Contact wear was observed on the faying surface of the retaining nut and piston head and the shoulder of the piston rod. These signatures were consistent with the nut not being tight enough to mitigate sliding of the piston head relative to the piston rod and retaining nut. It could not be determined if the manufacturer required a specific torque to be applied to the nut during assembly. Based on the evidence, it is likely that inadequate torque on the nut reduced the preload on the threaded section of the piston rod and contributed to premature fatigue crack propagation in the rod and its eventual failure. The failure of the piston rod allowed hydraulic fluid to pass freely from the down-side to the up-side of the piston, which prevented the hydraulic system from producing pressure to control the MLG's position. ## Factual narrative On January 19, 2017 about 1148 mountain standard time, a Beech 99A airplane, N326CA, experienced a landing gear collapse while landing at the Billings Logan International Airport, Billings, Montana. The commercial pilot was not injured; the airplane sustained substantial damage. The airplane was registered to and operated by Alpine Aviation Inc., d.b.a. Alpine Air, as a Title 14 Code of Federal Regulations Part 135 cargo transport flight. Visual meteorological conditions prevailed, and an instrument flight rules flight plan had been filed but was not activated. The flight departed from Dawson Community Airport, Glendive, Montana about 0945, with a planned destination of Sidney-Richland Municipal Airport, Sidney, Montana. The pilot reported that after departure, he retracted the landing gear and heard a "thud" sound. The landing gear "unsafe" light was illuminated, and the left landing gear light remained illuminated green, an indication that it was still extended despite the landing gear handle being in the retracted position. When reaching his initial destination of Sidney, the pilot performed a low pass over the runway to enable maintenance personnel on the ground to do a visual assessment. A mechanic reported to the pilot that the nose gear was in trail. The pilot diverted to Billings and the air traffic control personnel confirmed observing the nose gear extended at a 450 angle. The pilot further stated that he aligned with runway 28R and just prior to touch down, he feathered the propellers and decreased the airspeed. During touchdown, the right main landing gear collapsed, and the airplane came to rest on the centerline. As a result of the impact, the right aileron and right-wing spar was substantially damaged. Post-accident examination of the left landing gear actuator, part number (p/n) 99-388-008-1, revealed that it appeared to be fractured allowing the hydraulic fluid to pass freely from the downside to the upside, prohibiting pressure to control the landing gear's hydraulic system. Based on the pilots' statements about the landing, the fractured left landing gear was shipped to Textron Aviation, the airframe manufacturer, for examination. The piston rod, p/n 4A125C4, was separated into two pieces through several threads. According to the report, the damaged threads displayed crack propagation by fatigue. The final fracture was by overload and resulted in deformation of the damaged threads. The National Transportation Safety Board Materials Laboratory reviewed the Textron Aviation Materials report and pictures. The lab specialist reported that the fractography indicated that the piston rod failed in the threaded region by fatigue cracking over about 60% of the cross section due primarily to axial tension force. Contact wear was observed on the faying surface of the retaining nut, the shoulder of the piston rod, and on the faying surfaces of the piston head. These signatures were consistent with the nut not being tight enough tomitigate relative sliding of the piston head relative to the piston rod shoulder and the retaining nut. It could not be determined if the manufacturer required a specific torque to be applied to the nut during assembly. The airplane operator reported that the airplane had amassed 46,416.3 hours of total time in service. According to the maintenance records, the left actuator was last overhauled in November 2001, at which time the piston rod was replaced. The operator further reported that the part had acquired 7,445.2 hours equating to 8,267 cycles. The Beechcraft Model 99 Series Maintenance Manual stated that the landing gear hydraulic actuators should be overhauled or replaced every 10,000 hours. ## Aircraft - Registration: [N326CA](https://openairdocs.org/aircraft/N326CA), registered now, S/N U-135, built 1970 (OpenAirDocs) - Reported make and model: BEECH 99 (A) - Registry model: [Beech 99A](https://openairdocs.org/model/beech-99a) (registry code 1154003) (OpenAirDocs) - Registry engine: [Pratt & Whitney PT6A series](https://openairdocs.org/engine/pratt-whitney-pt6a-series) (registry code 52032, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: U-135 - Year built: 1970 - Airframe hours: 46422 - Engines: Pratt and Whitney PT6A-27 750 horsepower turbo prop; Pratt and Whitney PT6A-28 750 horsepower turbo prop - Damage: Substantial damage - Flight: Part 135 - Operator: Alpine Aviation Inc, doing business as Alpine Air - Registered owner: Alpine Aviation Inc - Airworthiness certificate: Standard, Normal - Last inspection: AAIP, December 14, 2016, 96 hours before - Departed: GDV, GLENDIVE, MT - Destination: SDY, SIDNEY, MT - Flight plan: IFR - Airport: BIL, Billings Logan Intl, runway 28R, 10,518 × 150 ft, asphalt - Equipment: Stall warning system, Onboard weather ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 25; injuries: none; commercial; airplane ratings: single-engine sea, single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review September 17, 2016; seat: left; restraint: 4-point; flight hours: 1,419 total, 270 in this make and model, 1,308 as pilot in command, 196 in the last 90 days, 57 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 230° at 12 knots - Visibility: 10 statute miles - Lowest ceiling: 10,000 ft broken - Temperature: 39 °F, dew point 21 °F - Altimeter: 29.48 inHg - Observed at: BIL ## 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 20170119001529A](https://openairdocs.org/incident/20170119001529A), Jan 19, 2017: Beech 99A, Billings, MT, Substantial damage. Aircraft took off from glendive mt airport and the pilot selected gear up. He noticed that he had an unsafe gear indication. He went through the emergency… ## Other investigations on N326CA (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 FTW82DA301](https://openairdocs.org/ntsb/FTW82DA301), Jul 28, 1982: Beech B99A (N326CA), Abilene, TX, substantial damage ## Docket (4 files) The files NTSB released with the investigation on January 15, 2020, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=94631. 7.7 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 2.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479874&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Textron Aviation Materials Report (item 2, .PDF, 4.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479875&FileExtension=.PDF&FileName=Textron%20Aviation%20Materials%20Report%20%20%20-Master.PDF - NTSB Materials Laboratory Comments on Textron Report (item 3, .PDF, 54 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479876&FileExtension=.PDF&FileName=NTSB%20Materials%20Laboratory%20Comments%20on%20Textron%20Report-Master.PDF - Manual Excerpts and Pictures (item 4, .PDF, 272 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40479877&FileExtension=.PDF&FileName=Manual%20Excerpts%20and%20Pictures-Master.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.