# NTSB WPR17IA007: Short Bros SD3 60 Sherpa, N148Z, Missoula, MT, October 13, 2016 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: October 13, 2016, 16:45 local (22:45 UTC) - Place: Missoula, MT - Coordinates: 46.916389, -114.090553 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=46.9164&lon=-114.0906&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Defining event: [Approach: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report November 6, 2019 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 94210 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17IA007 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/94210/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=94210 - Page: https://openairdocs.org/ntsb/WPR17IA007 ## Probable cause The failure of the nose landing gear down-lock piston to engage due to paint accumulation, which resulted in a nose landing gear collapse during landing. Also causal was the failure of the facility that performed the painting to comply with manufacturer guidance regarding painting of the airplane. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: gear extension and retract sys](https://openairdocs.org/ntsb-findings/01023230): Aircraft › Aircraft systems · Damaged/degraded (probable cause); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-findings/01023230/cases.md?model=8110101), [All aircraft, 416 cases](https://openairdocs.org/ntsb-findings/01023230/cases.md) - [Landing gear system: nose/tail gear strut/axle](https://openairdocs.org/ntsb-findings/01023222): Aircraft › Aircraft systems · Incorrect service/maintenance (probable cause); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-findings/01023222/cases.md?model=8110101), [All aircraft, 36 cases](https://openairdocs.org/ntsb-findings/01023222/cases.md) - [Landing gear system: nose/tail gear strut/axle](https://openairdocs.org/ntsb-findings/01023222): Aircraft › Aircraft systems · Inadequate inspection (probable cause); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-findings/01023222/cases.md?model=8110101), [All aircraft, 36 cases](https://openairdocs.org/ntsb-findings/01023222/cases.md) - [Oversight: oversight of maintenance](https://openairdocs.org/ntsb-findings/04032020): Organizational issues › Support/oversight/monitoring · Maintenance provider (probable cause); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-findings/04032020/cases.md?model=8110101), [All aircraft, 28 cases](https://openairdocs.org/ntsb-findings/04032020/cases.md) - [Maintenance: scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-findings/02062010/cases.md?model=8110101), [All aircraft, 320 cases](https://openairdocs.org/ntsb-findings/02062010/cases.md) - [Action: incorrect action performance](https://openairdocs.org/ntsb-findings/02041015): Personnel issues › Action/decision · Maintenance personnel (probable cause); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-findings/02041015/cases.md?model=8110101), [All aircraft, 1,386 cases](https://openairdocs.org/ntsb-findings/02041015/cases.md) - [Use of equip/info: use of available resources](https://openairdocs.org/ntsb-findings/02063035): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-findings/02063035/cases.md?model=8110101), [All aircraft, 41 cases](https://openairdocs.org/ntsb-findings/02063035/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Prior to flight: Aircraft maintenance event](https://openairdocs.org/ntsb-events/040); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-events/040/sequence.md?model=8110101), [All aircraft, 484 cases](https://openairdocs.org/ntsb-events/040/sequence.md) - [Prior to flight: Aircraft inspection event](https://openairdocs.org/ntsb-events/050); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-events/050/sequence.md?model=8110101), [All aircraft, 229 cases](https://openairdocs.org/ntsb-events/050/sequence.md) - [Approach: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) (defining event); cases with it: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-events/330/sequence.md?model=8110101), [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: [Short Bros SD3-60 SHERPA, 1 case](https://openairdocs.org/ntsb-events/094/sequence.md?model=8110101), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) ## Analysis The airline transport pilots reported that, during a ferry flight of an airplane that had just had been repainted, while on approach at its destination, the nose gear extended but failed to lock and subsequently collapsed on landing. Postaccident examination of the nose gear confirmed the nose gear's failure to lock, which led to its collapse. Observation of the nose gear down-lock actuator piston revealed that it had been painted, which prevented the piston from engaging and locking the nose gear during extension. Before the flight, maintenance personnel and the flight crew did not observe that the nose gear down-lock actuator piston area was painted. The airplane manufacturer issued a Service Information Letter (SIL) in 2007, that described a similar incident where the nose gear failed to lock in the down position on the first flight after an airplane had been repainted. The subsequent investigation revealed paint spray on the exposed piston of the nose landing gear down-lock actuator. The SIL stated "ensure that all masking material has been removed from the exposed piston after cleaning/painting, and that the piston is free from any paint or cleaning materials." Additionally, the landing gear emergency accumulator was observed during the preflight checks to be below the specified pressure. The accumulator was serviced to an adequate pressure prior to takeoff. Subsequently, the pressure bled down during the incident flight, and when the emergency landing gear extension was used by the flight crew, the accumulator did not have adequate pressure. According to the airplane manufacturer, the emergency landing gear extension is reliant on the main system pressure being depleted so that the emergency pressure can change a control valve position. Since the airplane's main hydraulic system was operative during the flight, the inability to use the landing gear emergency extension system, because of the lack of adequate pressure, would have been inconsequential, since the main system pressure was not depleted. ## Factual narrative On October 13, 2016, about 1645 mountain daylight time, a Short Bros SD3-60 Sherpa airplane, N148Z, sustained minor damage following a nose gear collapse during landing, at the Missoula International Airport (MSO) Missoula, Montana. The two airline transport pilots, were not injured. The airplane was registered to and operated by United States Department of Agriculture (USDA), as a public aircraft in support of the Forest Service. Visual meteorological conditions prevailed and a visual flight rules (VFR) flight plan was filed for the ferry flight which originated from Kingman Airport, Kingman, Arizona, about 1253. The pilots reported that prior to landing, they had an unsafe nose gear indication. After multiple unsuccessful attempts to get the nose gear to extend and indicate that it was down and locked, they decided to come in for a landing. During the landing roll, as the airplane's nose was lowered, the nose gear collapsed, and the forward section of the bottom of the fuselage, made contact with the runway surface. Once the airplane came to a stop, both pilots egressed. Examination of the airplane by the operator revealed minor damage on the underside of the fuselage. The airplane was returning to MSO, on its first flight, after being re-painted by a vendor in Kingman, Arizona. According to the operator, examination of the nose gear revealed that it failed to lock in the extended position and collapsed during landing. The flight crew attempted to extend and lock the nose gear during the flight but were unsuccessful. Post incident examination of the nose gear down-lock actuator piston (plunger), revealed that its chrome surface had been painted, which resulted in the locking piston not engaging, and prevented the locking of the nose gear during landing gear extension. The painting of the nose gear down-lock actuator piston was not observed by maintenance personnel or the flight crew on their pre-flight exterior checks. The airplane manufacturer Shorts issued a SD3-60 Sherpa Service Information Letter (SIL) Sherpa L-23, in April 2007, titled: Servicing/Painting – Removal of masking material/paint from nose landing gear down-lock actuator piston after cleaning/painting operations. The SIL described a similar incident where the nose gear failed to lock in the down position, on the first flight after the airplane had been re-painted. The subsequent investigation revealed paint spray on the exposed chrome piston of the nose landing gear down-lock actuator. The SIL stated "to ensure that all masking material has been removed from the exposed piston after cleaning/painting, and that the piston is free from any paint or cleaning materials." Additionally, the landing gear emergency accumulator was observed during the pre-flight checks to indicate below the specified pressure. The accumulator was serviced by maintenance to an adequate pressure, prior to takeoff. However, the pressure bled down during the incident flight, and when the emergency landinggear extension was used, the accumulator did not have adequate pressure. According to the operator's maintenance inspector, when activated, a fully serviced emergency accumulator forces the rapid application of hydraulic pressure into the system, however, according to the airplane's manufacturer, this is reliant on the main system hydraulic pressure being depleted so that the emergency pressure can change a control valve position. In this situation, the emergency pressure would be greater than the residual pressure of the failed main hydraulic system. ## Aircraft - Registration: [N148Z](https://openairdocs.org/aircraft/N148Z), registered now, S/N SH3428, built 1998 (OpenAirDocs) - Reported make and model: SHORT BROS SD3 60 SHERPA (SHERPA VAR) - Registry model: [Short Bros SD3-60 SHERPA](https://openairdocs.org/model/short-bros-sd3-60-sherpa) (registry code 8110101) (OpenAirDocs) - Registry engine: [Pratt & Whitney Canada PT6A-65AR](https://openairdocs.org/engine/pratt-whitney-canada-pt6a-65ar) (registry code 52277, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: SH3428 - Year built: 1994 - Airframe hours: 5203.6 - Engines: Pratt & Whitney PT6A-65R 1298 horsepower turbo prop; Pratt & Whitney PT6A-65R 1298 horsepower turbo prop - Damage: Minor damage - Flight: Ferry, Public use - Operator: USDA Forest Service - Registered owner: USDA Forest Service - Airworthiness certificate: None - Last inspection: Condition, June 24, 2016 - Departed: IGM, KINGMAN, AZ - Destination: MSO, MISSOULA, MT - Flight plan: VFR - Airport: MSO, Missoula Intl, runway 29, 9,501 × 150 ft, asphalt - Equipment: Angle of attack indicator, Auto-pilot, Data recorder ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 58; injuries: none; flight instructor, airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: helicopter, airplane; medical: class 2, with waivers/limitations; last flight review March 6, 2015; seat: left; restraint: 4-point; flight hours: 8,715 total, 148 in this make and model, 7,755 as pilot in command, 82 in the last 90 days, 12 in the last 30 days, 8 in the last 24 hours - Co-pilot; age 49; injuries: none; flight instructor, commercial, airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review March 2, 2016; seat: right; restraint: 4-point; flight hours: 6,424 total, 210 in this make and model, 4,921 as pilot in command, 90 in the last 90 days, 8 in the last 30 days, 8 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 360° at 6 knots - Visibility: 10 statute miles - Lowest ceiling: 7,000 ft overcast - Temperature: 46 °F, dew point 34 °F - Altimeter: 29.79 inHg - Observed at: MSO ## Docket (5 files) The files NTSB released with the investigation on July 5, 2018, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=94210. 4.8 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 3.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40464789&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Record of Email (item 2, .PDF, 139 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40464790&FileExtension=.PDF&FileName=Record%20of%20Email-Master.PDF - Service Information Letter (item 3, .PDF, 89 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40464791&FileExtension=.PDF&FileName=Service%20Information%20Letter-Master.PDF - Maintenance Manual Excerpts (item 4, .PDF, 848 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40464792&FileExtension=.PDF&FileName=Maintenance%20Manual%20Excerpts-Master.PDF - Incident Pictures (item 5, .PDF, 2 photos, 326 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40464793&FileExtension=.PDF&FileName=Incident%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.