# NTSB WPR17LA131: Cessna 421B, N380AL, Carlsbad, CA, June 22, 2017 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: June 22, 2017, 13:25 local (20:25 UTC) - Place: Carlsbad, CA - Coordinates: 33.127777, -117.282218 - Nearby events: https://openairdocs.org/map.md?lat=33.1278&lon=-117.2822&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: 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 95436 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17LA131 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95436/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95436 - Page: https://openairdocs.org/ntsb/WPR17LA131 ## Probable cause The right main landing gear collapse for undetermined reasons. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [Cessna 421B, 4 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=2076014), [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/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: [Cessna 421B, 7 cases](https://openairdocs.org/ntsb-events/094/sequence.md?model=2076014), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) - [Landing-landing roll: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Cessna 421B, 11 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=2076014), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot reported that touchdown on the runway and rollout were normal but that the airplane began to wobble as it decelerated to about 10 to 15 mph. He maintained directional control without braking. However, the wobble worsened, and the right main landing gear collapsed, which resulted in substantial damage to the right wing. Postaccident examination of the airplane revealed that the right main landing gear torque link pivot bolt assembly was severed, and the two inboard spacer washers, nut, and cotter pin were not located. Additionally, the the landing gear trunnion was partially separated from the wing structure. Vertical scuffing was observed on the outboard crown of the right main landing gear tire, which is consistent with the wheel skidding along the ground after becoming misaligned about 90° from normal. Metallurgical examination of the torque link pivot bolt revealed that the bolt fractured through the threaded region at the edge of the pivot barrel in bending overstress, with no evidence of preexisting cracking or corrosion. In addition, the trunnion fractured in overstress, with no evidence of preexisting fatigue cracks or fractures. Alignment of the wheel is achieved by washers installed between the upper and lower torque link assemblies; disconnection of the upper and lower torque link assemblies from one another could result in wheel misalignment, vibration, and ultimately failure of the main landing gear. However, due to postaccident damage to the landing gear and the unrecovered components, there was insufficient evidence available to determine why the right main landing gear collapsed. ## Factual narrative On June 22, 2017, about 1325 Pacific daylight time, a Cessna 421B, N380AL, was substantially damaged when it was involved in an accident in Carlsbad, California. The two pilots were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The pilot receiving instruction reported that the accident flight was the airplane’s first flight after extended maintenance. The pilot said they flew to Ramona, California, and conducted an uneventful landing before flying to Mc Clellan-Palomar Airport (CRQ), Carlsbad, California. He indicated that touchdown on runway 24 and rollout were normal but that, as the airplane decelerated to about 10 to 15 mph, it started to wobble. The pilot maintained directional control without using brakes, but the wobbling intensified; suddenly the right main landing gear collapsed, and the right wing and engine struck the ground, resulting in substantial damage to the wing. The flight instructor reported that the approach and landing were normal and that after touchdown, the airplane decelerated "nicely.” He stated that just before they reached taxiway A5, he noticed what felt like a flat tire or oscillation in the gear and asked the pilot to "keep it straight." The instructor recalled that the pilot responded that he wasn't going to brake. A few seconds later, the right main landing gear collapsed, and the airplane rotated toward taxiway N3. The instructor estimated that the airplane’s speed at the time of the gear oscillation was between 5-10 mph. He added that when he learned the bolt that connected the "torque links or scissors" on the right main landing gear assembly had failed, this would explain "how the assembly rotated and then collapsed backwards when the tire became misaligned with the aircraft's momentum." Postaccident examination of the airplane revealed that the right main landing gear torque link pivot bolt assembly was severed, and the two inboard spacing washers, nut, and cotter pin were not located (see Figure 1). Additionally, the landing gear trunnion was partially separated from the wing structure, and the right main landing gear was separated but remained attached via hydraulic hoses. Figure 1: Service Kit SK421-118 overview of the torque link assembly and associated part with annotated references to the missing parts. Further examination of the right main landing gear revealed that the forward right landing gear trunnion was separated into two pieces, with the lower portion torn away from the upper portion. Scraping was observed on the outboard side of the landing gear strut and brake caliper. The right main landing gear tire exhibited vertical scuffing along its outboard crown. Additional multidirectional striations were observed on the outboard portion of the lower torque link assembly, brake caliper, and lower portion of the landing gear strut assembly. (The upper and lower landing gear strut are interconnected by the upper and lower torque linkassemblies. Alignment of the wheel, which is connected to the lower portion of the landing gear strut, is obtained by washers installed between the upper and lower torque link assemblies.) Portions of the right landing gear trunnion, right landing gear brace assembly, and the upper torque link assembly, along with the torque link pivot bolt, were sent to the National Transportation Safety Board Materials Laboratory for further examination. Metallurgical examination revealed that the torque link pivot bolt was fractured through the threaded region at the edge of the pivot barrel. The fracture surface was partially obscured by red rust deposits but exhibited surface texture, surface topography, and deformation patterns indicative of a bending overstress fracture. No indications of preexisting cracking or corrosion were found. The pieces of the trunnion and the rest of the submitted parts exhibited fractures consistent with overstress, with no indications of preexisting fractures or fatigue cracks. ## Aircraft - Registration: [N380AL](https://openairdocs.org/deregistered/N380AL-2020-02-28), registration cancelled 2020-02-28, S/N 421B0329, built 1972 (OpenAirDocs) - Reported make and model: CESSNA 421B (B) - Registry model: [Cessna 421B](https://openairdocs.org/model/cessna-421b) (registry code 2076014) (OpenAirDocs) - Registry engine: [Continental GTSIO-520-C](https://openairdocs.org/engine/continental-gtsio-520-c) (registry code 17035, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 421B0329 - Year built: 1972 - Engines: CONT MOTOR GTSIO-520-C 340 horsepower reciprocating; CONT MOTOR GTSIO-520-C 340 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Airworthiness certificate: Standard, Normal - Departed: F70, Temecula, CA - Destination: CRQ, Carlsbad, CA - Airport: CRQ, Mc Clellan-Palomar, runway 24, 4,897 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 46; injuries: none; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, with waivers/limitations; last flight review February 3, 2017; seat: left; restraint: 3-point; flight hours: 2,830 total, 0.5 in this make and model, 2,708 as pilot in command, 10.5 in the last 90 days - Pilot; age 57; injuries: none; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1; seat: right; restraint: 3-point ## Weather - Conditions: Visual (VMC), Day - Wind: 250° at 9 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 70 °F, dew point 61 °F - Altimeter: 29.84 inHg - Observed at: KCRQ ## 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 20170622021759A](https://openairdocs.org/incident/20170622021759A), Jun 22, 2017: Cessna 421B, Carlsbad, CA, Substantial damage. After what was reported as a normal landing, during roll-out, the right landing gear collapsed. The pilots stated that the aircraft was only travelling at… ## Docket (9 files) The files NTSB released with the investigation on December 30, 2020, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95436. 26.9 MB in all. - NTSB lab examination (item 1, PDF, 2 pages, 119 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11362325&FileExtension=pdf&FileName=4%20NTSB%20LAb%20Exam%20Report_Redacted-Rel.pdf - NTSB materials laboratory photos (item 2, PDF, 5 pages, 13 photos, 766 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11627212&FileExtension=pdf&FileName=Images%20of%20pieces%20evaluated-Rel.pdf - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 3, PDF, 9 pages, 14.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11362904&FileExtension=pdf&FileName=1%206120%20redacted-Rel.pdf - Flight instructor statement (item 4, PDF, 2 pages, 97 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11362784&FileExtension=pdf&FileName=2%20cfi%20statement_Redacted-Rel.pdf - Record of conversation - FAA inspector (item 5, PDF, 1 page, 71 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11362914&FileExtension=pdf&FileName=6%20Record%20of%20Conversation%20faa-Rel.pdf - Landing gear examination summary (item 6, PDF, 5 pages, 5 photos, 2.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11362156&FileExtension=pdf&FileName=3%20ntsb%20landing%20gear%20exam_Redacted-Rel.pdf - Service kit SK421-118 (item 7, PDF, 3 pages, 89 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11759963&FileExtension=pdf&FileName=SK421-118-Rel.pdf - Illustrated parts catalog - main gear strut installation (item 8, PDF, 3 pages, 135 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11760340&FileExtension=pdf&FileName=IPC%20-%20MLG%20Strut-Rel.pdf - Photos of the accident airplane - courtesy of the FAA (item 9, PDF, 16 pages, 16 photos, 8.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11763182&FileExtension=pdf&FileName=Photo%201_Redacted-Rel.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.