# NTSB WPR22LA124: Cessna 310R, N3UR, McGrath, AK, March 10, 2022 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: March 10, 2022, 14:30 local (23:30 UTC) - Place: McGrath, AK - Coordinates: 62.952784, -155.60704 - Nearby events: https://openairdocs.org/map.md?lat=62.9528&lon=-155.6070&mi=10 - Phase of flight: [Taxi](https://openairdocs.org/ntsb-phases/250) (OpenAirDocs' grouping) - Defining event: [Taxi-into takeoff position: Landing gear collapse](https://openairdocs.org/ntsb-events/094) - Highest injury: No injuries - Injuries: 4 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: FSDO PMI, Textron Aviation - NTSB case key (mKey): 104790 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR22LA124 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/104790/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=104790 - Page: https://openairdocs.org/ntsb/WPR22LA124 ## Probable cause A failure of the right main landing gear bellcrank lower arm fork, bellcrank, pivot bolt, and trunnion bellcrank lug for undetermined reasons. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: main landing gear attach sec](https://openairdocs.org/ntsb-findings/01023211): Aircraft › Aircraft systems · Failure (probable cause); cases with it: [Cessna 310R, 2 cases](https://openairdocs.org/ntsb-findings/01023211/cases.md?model=2074245), [All aircraft, 66 cases](https://openairdocs.org/ntsb-findings/01023211/cases.md) - [Landing gear system](https://openairdocs.org/ntsb-findings/01023200): Aircraft › Aircraft systems · Unknown/Not determined (probable cause); cases with it: [Cessna 310R, 1 case](https://openairdocs.org/ntsb-findings/01023200/cases.md?model=2074245), [All aircraft, 113 cases](https://openairdocs.org/ntsb-findings/01023200/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Taxi-into takeoff position: Landing gear collapse](https://openairdocs.org/ntsb-events/094) (defining event); cases with it: [Cessna 310R, 8 cases](https://openairdocs.org/ntsb-events/094/sequence.md?model=2074245), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) ## Analysis The pilot back-taxied the airplane for departure and then began a 180° left turn to align the airplane with the runway centerline when the right main landing gear collapsed. The gear collapse resulted in substantial damage to the right elevator. A postaccident examination of the airplane revealed fractures to the bellcrank lower arm fork, bellcrank, pivot bolt, and trunnion bellcrank lug at the right main landing gear, which all displayed signatures consistent with overstress. The airplane had recently been repaired following another right main landing gear failure. During the repair the accident pilot, who was also the mechanic, adjusted the down lock tension as required by the maintenance manual and returned the airplane to service after he determined that the tension was within limits. A statement from the airplane manufacturer suggested that the failure may have been the result of an improper down lock tension adjustment. However, there was insufficient evidence in the investigation to show whether the pilot performed the adjustment incorrectly, thus the cause of the landing gear failure is undetermined. ## Factual narrative On March 10, 2022, about 1430 Alaska daylight time, a Cessna 310R airplane, N3UR, was substantially damaged when it was involved in an accident near McGrath, Alaska. The pilot and three passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he back-taxied along runway 16 towards the departure end of the runway at McGrath Airport (PAMC). When he arrived at the end of the runway, he started to turn to the airplane to align it with the reciprocal runway. However, as he began the turn, the right main landing gear collapsed and the wing and propeller both contacted the runway. The right elevator also contacted the runway and was substantially damaged. A postaccident examination of the right main landing gear well by the pilot found fractures at the bellcrank lower arm fork (item “1” in Figure 1), bellcrank pivot bolt (item “2 in Figure 1), and the trunnion bellcrank lug (item “3” in Figure 2). An NTSB materials laboratory review of photographs of the fracture surfaces revealed fracture characteristics that were all consistent with overstress. No evidence of fatigue was observed on any of the fracture faces; however, the quality of the photographs precluded the observation of any small regions that may have exhibited fatigue cracking. According to the airplane manufacturer, an overstress failure of the bell crank assembly at the trunnion is commonly an indication that the down lock side brace was not in the down and locked position. Figure 1: Bellcrank assembly fracture points Figure 2: Bellcrank bolt fracture at trunnion A logbook entry from the airplane’s most recent annual inspection indicated that the right main landing gear door and gear strut were removed and replaced with new bolts. The landing gear was subsequently re-rigged in accordance with the maintenance manual before the airplane was returned to service. The accident pilot was also the certified airframe and powerplant mechanic responsible for completing the last annual inspection on the accident airplane. According to his recount, after he replaced the landing gear strut after a previous right main landing gear failure, he checked the down lock tension and discovered that it was “too tight.” However, when he subsequently made an adjustment to reduce the tension, he found that it was out of tolerance. He made one final adjustment that placed the down lock tension within tolerance before he returned the airplane to service, 22 flight hours prior to the accident. The accident airplane maintenance manual provided specific instructions for adjusting main landing gear down lock tension (Chapter 32, Section 32-30-00). “(1) Inspection the main gear down lock tension for proper adjustment (a) Position landing gear in down position (b) Check main gear down lock for proper engagement and tension (40 to 60 pounds) NOTE: When checking down lock tension always place a finger on the down lock switch, pull scaleat a right angle to the lock link and read the scale at the point when switch actuation can be felt. (2) Adjustment (a) If the down lock tension is not 40 to 60 pound, adjust push-pull tube in one half turn increments until proper tension is obtained. If the down lock tension is in excess of 60 pounds, the down lock tension should be rigged to 40 to 50 pounds. Lengthening the push-pull tube decreases and shortening the push-pull tube increases tension.” The pilot recalled using a spring scale to measure the down lock tension and the push-pull tube to adjust the tension. He added that he was particular about following each step in the Cessna maintenance manual during this inspection as he was new to maintaining the accident airplane make and model. ## Aircraft - Registration: [N3UR](https://openairdocs.org/deregistered/N3UR-2023-06-15), registration cancelled 2023-06-15, S/N 310R0061, built 1974 (OpenAirDocs) - Reported make and model: CESSNA 310R - Registry model: [Cessna 310R](https://openairdocs.org/model/cessna-310r) (registry code 2074245) (OpenAirDocs) - Registry engine: [Continental IO-520 series](https://openairdocs.org/engine/continental-io-520-series) (registry code 17032, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 310R0061 - Year built: 1974 - Airframe hours: 7893.6 - Engines: Continental Motors IO-520-M1B 285 horsepower reciprocating; Continental Motors IO-520-M1B 285 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, January 12, 2022, 22 hours before - Destination: PARY, Ruby, AK - Airport: PAMC, McGrath, runway 16, 5,936 × 100 ft, asphalt - Equipment: Auto-pilot, Handheld GPS, Stall warning system ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 73; injuries: none; flight engineer, airline transport, commercial, flight instructor; airplane ratings: single-engine sea, single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review December 22, 2021; seat: left; restraint: 3-point; flight hours: 35,774 total, 54 in this make and model, 25,132 as pilot in command, 45 in the last 90 days, 60 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 10° at 9 knots - Visibility: 10 statute miles - Lowest ceiling: 2,200 ft overcast - Temperature: 25 °F, dew point 18 °F - Altimeter: 29.72 inHg - Observed at: PAMC - METAR: PAMC 102353Z 01009KT 10SM OVC022 M04/M08 A2972 RMK AO2 SLP072 60001 T10441078 11039 21067 58011 ## 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 20220310003209A](https://openairdocs.org/incident/20220310003209A), Mar 10, 2022: Cessna 310R, Mcgrath, AK, Substantial damage. The pilot reported that while back-taxing to reposition for departure, during a left 180 turn, the right landing gear collapsed. Subsequently, the right wing… ## Docket (10 files) The files NTSB released with the investigation on January 31, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=104790. 9.2 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14439165&FileExtension=pdf&FileName=6120_Redacted-Rel.pdf - Record of conversations (item 2, PDF, 2 pages, 124 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14454957&FileExtension=pdf&FileName=record%20of%20conversations-Rel.pdf - Pilot email correspondence (item 3, PDF, 2 pages, 198 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14465389&FileExtension=pdf&FileName=Pilot%20followup%20email_Redacted-Rel.pdf - NTSB materials laboratory report (item 4, PDF, 2 pages, 160 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14439008&FileExtension=pdf&FileName=NTSB%20materials%20lab%20report_Redacted-Rel.pdf - Logbook excerpt (item 5, PDF, 6 pages, 3.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14463098&FileExtension=pdf&FileName=Excerpt%20from%20aircraft%20log_Redacted-Rel.pdf - Figures of failure areas (item 6, PDF, 2 pages, 2.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14438736&FileExtension=pdf&FileName=figure%20of%20failure%20areas-Rel.pdf - Landing gear excerpt from maintenance manual (item 7, PDF, 5 pages, 135 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14445070&FileExtension=pdf&FileName=Excerpt%20from%20maintenance%20manual-Rel.pdf - Down lock tension excerpt from maintenance manual (item 8, PDF, 5 pages, 141 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14449694&FileExtension=pdf&FileName=Excerpt%20from%20MM%20down%20lock%20tension-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 9, PDF, 1 page, 96 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14450782&FileExtension=pdf&FileName=Release%20of%20Wreckage%20completed_Redacted-Rel.pdf - Accident photographs (item 10, PDF, 5 pages, 933 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14456488&FileExtension=pdf&FileName=accidenet%20photographs-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.