# NTSB WPR15IA252: Cirrus SR22, N915TD, Scottsdale, AZ, August 27, 2015 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: August 27, 2015, 14:05 local (21:05 UTC) - Place: Scottsdale, AZ - Coordinates: 33.622776, -111.910552 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.6228&lon=-111.9106&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: 3 uninjured - Status: Completed, report June 5, 2018 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Cirrus Aircraft Design Corp, Federal Aviation Administration - NTSB case key (mKey): 91881 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR15IA252 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/91881/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=91881 - Page: https://openairdocs.org/ntsb/WPR15IA252 ## Probable cause The failure of the nose landing gear due to unanticipated fatigue loads. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: nose/tail landing gear](https://openairdocs.org/ntsb-findings/01023220): Aircraft › Aircraft systems · Fatigue/wear/corrosion (probable cause); cases with it: [Cirrus Design SR22, 1 case](https://openairdocs.org/ntsb-findings/01023220/cases.md?model=2130001), [All aircraft, 185 cases](https://openairdocs.org/ntsb-findings/01023220/cases.md) - [Landing gear system: nose/tail landing gear](https://openairdocs.org/ntsb-findings/01023220): Aircraft › Aircraft systems · Capability exceeded (probable cause); cases with it: [Cirrus Design SR22, 1 case](https://openairdocs.org/ntsb-findings/01023220/cases.md?model=2130001), [All aircraft, 185 cases](https://openairdocs.org/ntsb-findings/01023220/cases.md) - [Landing gear system: nose/tail landing gear](https://openairdocs.org/ntsb-findings/01023220): Aircraft › Aircraft systems · Failure (probable cause); cases with it: [Cirrus Design SR22, 1 case](https://openairdocs.org/ntsb-findings/01023220/cases.md?model=2130001), [All aircraft, 185 cases](https://openairdocs.org/ntsb-findings/01023220/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing-landing roll: Landing gear collapse](https://openairdocs.org/ntsb-events/094) (defining event); cases with it: [Cirrus Design SR22, 5 cases](https://openairdocs.org/ntsb-events/094/sequence.md?model=2130001), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) - [Landing-landing roll: Miscellaneous/other](https://openairdocs.org/ntsb-events/900); cases with it: [Cirrus Design SR22, 23 cases](https://openairdocs.org/ntsb-events/900/sequence.md?model=2130001), [All aircraft, 1,556 cases](https://openairdocs.org/ntsb-events/900/sequence.md) - [Landing-landing roll: Attempted remediation/recovery](https://openairdocs.org/ntsb-events/060); cases with it: [Cirrus Design SR22, 11 cases](https://openairdocs.org/ntsb-events/060/sequence.md?model=2130001), [All aircraft, 1,422 cases](https://openairdocs.org/ntsb-events/060/sequence.md) ## Analysis ***This report was modified on August 1, 2018. Please see the docket for this incident to view the original report.*** While the pilot receiving instruction was landing the airplane, the main landing gear touched down first; as he was slowly lowering the nose landing gear (NLG) to the runway, he felt a "shimmy" in the NLG. Despite applying back pressure to lift the weight off the NLG, the airplane's nose slowly started falling forward, and the nosewheel collapsed. Postincident examination of the airplane revealed that the NLG was fractured through the strut tube adjacent to the forward edge of the gusset tube attachment welds. Metallurgical testing revealed that the failure was the result of high-stress fatigue cracking due to sideways bending from one side. No mechanical or metallurgical anomalies were noted with the NLG. After the incident, the airplane manufacturer conducted structural testing of the NLG, which revealed that shimmy events or nonstandard towing could result in cracks and the eventual separation of the NLG. As a result, the airplane manufacturer issued two service advisory letters, which outlined appropriate towing and inspection procedures. The airplane manufacturer also issued a series of service bulletins, which, in part, recommended that all NLG on the affected airplanes be inspected for cracks in the welds between the strut tube and the gusset tubes and that postshimmy inspections also be conducted to look for cracks in this area. Additionally, the airplane manufacturer updated the design of the NLG to increase the strength of the strut tube. ## Factual narrative On August 27, 2015, about 1405 mountain standard time, a Cirrus SR22, N915TD, experienced a nose landing gear collapse during landing roll at Scottsdale Airport (SDL), Scottsdale, Arizona. The certified flight instructor (CFI), the pilot receiving instruction, and one passenger were not injured. The airplane received minor damage. The airplane was registered to ESPBC LLC of Scottsdale, and operated by Scottsdale Executive Flight Training as a 14 Code of Federal Regulations Part 91 instructional cross-country flight. Visual meteorological conditions prevailed, and a flight plan was not filed. The flight originated from Flagstaff, Arizona about 1300, and was destined for SDL. According to the CFI, the pilot receiving instruction made the landing. The main landing gear touched down first, and slowly the nose gear was lowered onto the runway's surface. The CFI reported that at this time they felt a shimmy in the nose gear, during which the pilot receiving instruction applied back pressure on the stick to lift the weight off the nose gear. As the nose gear came down a second time, it appeared that the shimmy had stopped, and that they were level on all three wheels. However, after a few seconds the nose slowly started falling forward until it had completely collapsed. The nose landing gear consists of a main strut tube and two gusset tubes near the top portion of the main strut tube. The landing gear was observed fractured through the strut tube adjacent to the forward edge of the gusset tube attachment welds. The National Transportation Safety Board Materials Laboratory examined the nose landing gear strut and determined that the failure of the landing gear was the result of high stress fatigue cracking due to sideways bending from one side. No mechanical or metallurgical anomalies were noted with the landing gear. On March 7, 2016, Cirrus Design Corporation issued Service Advisory Letter SA 16-03, entitled "Nose Landing Gear Strut Assembly Inspection, which denoted the following: • Cracks have been discovered on the nose landing gear strut assembly at the welds between the strut tube and the LH and RH gusset tubes. • A visual inspection of the welds between the strut tube and the LH and RH gusset tubes for cracks must be performed every time the engine cowling is removed. • If cracks are found, the aircraft is prohibited from flight until the nose landing gear strut assembly is replaced. (Refer to AMM-32-20) On April 12, 2016, Cirrus Design Corporation issued Service Advisory Letter SA 16-05, entitled "Aircraft Towing Guidance." The SA was based on the potential for damage to the nose landing gear due to loading from non-standard and abusive tug operation. The SA was released offering aircraft towing guidance. This guidance included the following; • When towing aircraft, do not stop/start abruptly, especially when the tow bar is at an angle greater than 45° either side of center. • When positioning the aircraft with a towing vehicle, the angle ofthe tow bar must be less than 45° either side of center for both pulling and pushing. Hand towing must be used if angles greater than 45° either side of center are needed for positioning. • Do not tow aircraft at speeds higher than 15 mph. Additionally, Cirrus Design Corporation performed structural testing of the nose landing gear. Based on the data provided by the NTSB metallurgy lab, and a video of an incident in Japan where an airplane experienced a nose landing gear shimmy, Cirrus explored two different methods of producing side loads in the nose landing gear. The first was through taxi and towing, the second through shimmy. Flight testing showed that significant side loads on the nose landing gear would develop during a shimmy event. As a result of the testing, Cirrus did the following: On April 12, 2016, Cirrus Design Corporation Service Bulletin SB2X-32-22, entitled "NOSE GEAR – Nose Landing Gear Strut Assembly Inspection," was issued. The bulletin, which Cirrus considers mandatory, was issued with instructions to inspect all nose landing gear in the field for cracks in the welds between the strut tube and the LH and RH gusset tubes. In addition to the one-time inspection required by the Service Bulletin, Cirrus added a post-shimmy inspection to Chapter 5-50 Unscheduled Maintenance Checks of the Aircraft Maintenance Manual (AMM). Similar to the hard/overweight landing inspection, this post-shimmy inspection would look specifically for cracks at the gusset welds exactly as noted in the Service Bulletin. (For additional information, refer to the Service Bulletin, which is appended to the docket for this report.) On July 14, 2017, Cirrus Design Corporation Service Bulletin SB2X-32-22R1 was issued. The bulletin, which Cirrus considers mandatory, was revised to update Compliance, Effectivity, Purpose, Manpower Requirements, and Accomplishment instructions. The bulletin specifically states, "Operators who have successfully complied with the original release of this service bulletin, dated April 12, 2016, must complete Revision 1 of this Service Bulletin in its entirety, and must continue to perform this Service Bulletin every 50 hours thereafter until termination action occurs. (For additional information, refer to the revised Service Bulletin, which is appended to the docket for this report.) On January 5, 2018, Cirrus Design Corporation Service Bulletin SB2X-32-22R2 was issued. The bulletin, which Cirrus considers mandatory, was revised to update Compliance and Effectivity. The bulletin specifically states, "Operators who have successfully complied with the original release of this service bulletin, dated April 12, 2016, must complete Revision 2 of this Service Bulletin in its entirety, and must continue to perform this Service Bulletin every 50 hours thereafter until termination action occurs. (For additional information, refer to the revised Service Bulletin, which is appended to the docket for this report.) On July 14, 2017, Cirrus DesignCorporation Service Bulletin SB2X-32-23, which Cirrus considered to be mandatory, entitled "NOSE GEAR – Nose Wheel Shimmy Reduction," was issued. The bulletin noted that on affected airplanes, nose wheel shimmy may exist on aircraft equipped with Beringer wheels. The bulletin states that a nose tire vibration due to imbalance or tire damage can be mistaken for NLG shimmy. However, it is advisable that both conditions be examined closely and considered tandem during aircraft inspection. The bulletin contains instructions for the adjustment of the nose tire pressure and force required to rotate the nose wheel fork. (For additional information, refer to the Service Bulletin, which is appended to the docket for this report.) On January 5, 2018, Cirrus Design Corporation issued revised Service Bulletin SB2X-32-23R1. The bulletin, which is considered mandatory, was revised to update Effectivity, Purpose, and Accomplishment Instructions. The bulletin states that operators who have successfully complied with the original release of this Service Bulletin, dated July 14, 2017, must complete Revision 1 of this Service Bulletin in its entirety. The Service Bulletin contains instructions for the adjustment of the nose tire pressure and the verification of the force required to rotate the nose wheel fork. (For additional information, refer to the revised Service Bulletin, which in appended to the docket for this report.) On July 14, 2017, Cirrus Design Corporation issued Cirrus Service Advisory (SA) SA17-08, entitled "Possible Cracking at Nose Land Gear Fillet Welds." The SA revealed that cracks had been discovered on some nose landing gear (NLG) strut assemblies at the fillet welds between the strut tube and the LH and RH gusset tubes. These cracks had led to the collapse of the NLG assemblies. The SA further revealed that each of the aircraft involved had a history of excessive nose wheel shimmy following touchdown of the nose landing gear. The SA defined "nose wheel shimmy" as "a lateral oscillation or wobble of the NLG resulting in a shaking feeling throughout the cabin of the aircraft that can vary in intensity." This is normally encountered during the landing roll-out and will subside as speed is reduced. Cirrus noted in the "Actions" section of the SA that nose wheel shimmy can be reduced or eliminated by lowering the tire pressure. Prior to the next flight, adjust the tire pressure on the nose landing gear to 40 – 50 psi (276 – 344 kPa). (For additional information, refer to the Service Advisory, which is appended to the docket for this report.) On January 5, 2018, Cirrus Design Corporation issued revised Service Advisory SA17-08R1 (revision 1). The Advisory was issued to update Effectivity and the NLG tire pressure as outlined in SA17-08, dated July 14, 2017. Cirrus noted in the "Actions" section of the SA that nose wheel shimmy can be reduced or eliminated by lowering the tire pressure. Prior to the next flight, adjust the tire pressure on the noselanding gear to 30 – 35 psi (207 – 241 kPa). (For additional information, refer to the Service Advisory, which is appended to the docket for this report.) Cirrus Aircraft also incorporated specific emphasis and recommendations on how to further discourage shimmying on landing and actions to be taken if the situation occurs on landing in their pilot training program. These incorporations are included in the Landing Standardization Course. Maintenance guidance is also available to mechanics following a shimmy event. To increase the strength of the weld in the critical area on the nose landing gear, the thickness of the main strut tube was analyzed with an increased wall thickness from 0.125-inch to the full thickness of 0.156-inch. The result of the analysis was an increase (3-5%) in the local stress levels in the static analysis. This design change has been made for all new and replacement gear. ## Aircraft - Registration: [N915TD](https://openairdocs.org/aircraft/N915TD), registered now, S/N 4098, built 2014 (OpenAirDocs) - Reported make and model: CIRRUS SR22 - Registry model: [Cirrus Design SR22](https://openairdocs.org/model/cirrus-design-sr22) (registry code 2130001) (OpenAirDocs) - Registry engine: [Continental IO-550-N](https://openairdocs.org/engine/continental-io-550-n) (registry code 17215, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 4098 - Year built: 2014 - Airframe hours: 391.4 - Engines: Continental Motors IO-550 310 horsepower reciprocating - Damage: Minor damage - Flight: Instructional, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, May 27, 2015, 93 hours before - Departed: FLG, Flagstaff, AZ - Destination: SDL, Scottsdale, AZ - Airport: SDL, Scottsdale, runway 210, 8,249 × 100 ft, asphalt - Equipment: Electronic multifunction display, Electronic primary flight display, Onboard weather, Satellite tracking device, Stall warning system, Airframe parachute, Auto-pilot, Data recorder ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 29; injuries: none; flight instructor, commercial; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, with waivers/limitations; last flight review January 20, 2015; seat: right; restraint: 3-point; flight hours: 783 total, 60 in this make and model, 699 as pilot in command, 326 in the last 90 days, 88 in the last 30 days, 2 in the last 24 hours - Student pilot; age 52; injuries: none; last flight review January 20, 2015; seat: left; restraint: 3-point; flight hours: 500 total, 365 in this make and model, 17 in the last 90 days, 9 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 70° at 3 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 104 °F, dew point 57 °F - Altimeter: 29.93 inHg - Observed at: SDL ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Incident 20150827019989I](https://openairdocs.org/incident/20150827019989I), Aug 27, 2015: Cirrus Design Corp SR22, Scottsdale, AZ, Minor damage. Aircraft landed on runway 21 at sdl. After approximaitly 1000 feet the nose gear collapsed under the aircraft. The nose gear mount brace was found cracked at… ## Docket (9 files) The files NTSB released with the investigation on March 22, 2018, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=91881. 20.0 MB in all. - Materials Laboratory Factual Report 16-012 (item 1, .PDF, 6.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40461194&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2016-012-Master.PDF - Cockpit Display - Recorded Flight Data - Specialist's Factual Report (item 2, .PDF, 952 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40461195&FileExtension=.PDF&FileName=Cockpit%20Display%20-%20Recorded%20Flight%20Data%20-%20Specialist%27s%20Factual%20Report-Master.PDF - Cockpit Display - Recorded Flight Data - Specialist's Factual Report - Attachment 1 - Tabular Data (CSV) (item 3, .CSV, 332 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40461196&FileExtension=.csv&FileName=Cockpit%20Display%20-%20Recorded%20Flight%20Data%20-%20Specialist%27s%20Factual%20Report%20-%20Attachment%201%20-%20Tabular%20Data%20(CSV)-Master.csv - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 4, .PDF, 4.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40461197&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Cirrus Service Bulletins (item 5, .PDF, 5.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40461198&FileExtension=.PDF&FileName=Cirrus%20Service%20Bulletins-Master.PDF - Cirrus Service Advisories (item 6, .PDF, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40461199&FileExtension=.PDF&FileName=Cirrus%20Service%20Advisories-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 7, .PDF, 102 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40461200&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master.PDF - Photo Array (item 8, .PDF, 3 photos, 450 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40461201&FileExtension=.PDF&FileName=Photo%20Array-Master.PDF - Revision to Analysis and PC (item 9, .PDF, 42 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40465698&FileExtension=.PDF&FileName=Revision%20to%20Analysis%20and%20PC-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.