# NTSB ERA11LA484: North American TB-25N, N9079Z, Georgetown, DE, September 4, 2011 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: September 4, 2011, 17:45 local (21:45 UTC) - Place: Georgetown, DE - Coordinates: 38.686111, -75.355003 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=38.6861&lon=-75.3550&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: 5 uninjured - Status: Completed, report August 29, 2012 - Report: Approved by Office Director - NTSB office: Eastern Region Aviation - Parties: S & R Aviation Services, Inc., FAA/FSDO - NTSB case key (mKey): 81732 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA11LA484 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/81732/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=81732 - Page: https://openairdocs.org/ntsb/ERA11LA484 ## Probable cause Maintenance personnel's inadequate examination of the main landing gear during the airplane’s most recent conditional inspection, which resulted in the fatigue failure of the right main landing gear shock strut drag arm during the landing roll. ## 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 · Inadequate inspection (probable cause); cases with it: [North American TB-25N, 1 case](https://openairdocs.org/ntsb-findings/01023211/cases.md?model=6400714), [All aircraft, 66 cases](https://openairdocs.org/ntsb-findings/01023211/cases.md) - [Inspection: scheduled/routine inspection](https://openairdocs.org/ntsb-findings/02061520): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [North American TB-25N, 1 case](https://openairdocs.org/ntsb-findings/02061520/cases.md?model=6400714), [All aircraft, 167 cases](https://openairdocs.org/ntsb-findings/02061520/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: [North American TB-25N, 1 case](https://openairdocs.org/ntsb-events/094/sequence.md?model=6400714), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) - [Landing-landing roll: Runway excursion](https://openairdocs.org/ntsb-events/300); cases with it: [North American TB-25N, 1 case](https://openairdocs.org/ntsb-events/300/sequence.md?model=6400714), [All aircraft, 3,643 cases](https://openairdocs.org/ntsb-events/300/sequence.md) ## Analysis According to both pilots, they landed the airplane and felt the right wing drop during the landing roll. They attempted to maintain directional control, but the right wing dropped further and the airplane veered off of the right side of the runway. During a subsequent examination of the wreckage, the right main landing gear shock strut drag arm was found broken. An examination of the broken drag arm revealed that it fractured in the I-beam at the blend radius of an orthogonal arm due to bending fatigue. Given the extent of fatigue crack propagation in the flange of the I-beam, it is likely that the fracture occurred due to high-cycle, low-stress fatigue. Since the depth of the fatigue crack was significant relative to the I-beam flange thickness, the fatigue crack probably developed and propagated over a long time under numerous low-stress cycles. The most recent inspection of the main landing gear was on July 7, 2011, which was in accordance with a conditional inspection. The inspection required a mechanic to verify the condition and security of the main landing gear. It is most likely that the fatigue crack would have been detectable at the time of that inspection. ## Factual narrative On September 4, 2011, about 1745 eastern daylight time, a North American TB-25N, N9079Z, was substantially damaged during the landing rollout at Sussex County Airport (GED), Georgetown, Delaware. The two pilots and three passengers on board were not injured. The airplane was registered to a corporation and operated under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and there was no flight plan filed. The flight originated from Patuxent River Naval Air Station (NHK), Patuxent River, Maryland, about 1700. According to both pilots, they landed the airplane and during the landing rollout, they felt the right wing drop and heard a noise like "a blown tire." They attempted to maintain directional control of the airplane, but the right wing dropped further and the airplane veered off of the right side of the runway. The airplane came to rest in the grass beside the runway; the pilots secured the airplane, and then exited without incident. During a subsequent examination of the wreckage, a Federal Aviation Administration (FAA) inspector discovered that the airplane sustained substantial damage to the right engine firewall. Also, the right main landing gear shock strut drag arm was found broken. According to the pilot, he held a commercial pilot certificate for airplane multiengine land, a private pilot certificate for airplane single-engine land, and an instrument airplane rating. He also held a type certificate rating for the North American BE25. His most recent second-class medical certificate was issued on January 12, 2011. He reported 4,633 total hours of flight time, of which, 1,344 hours were in the same make and model as the accident airplane. According to FAA records, the copilot held a flight instructor certificate for airplane single-engine land, airplane multiengine land, and instrument airplane. He also held a type rating for the North American BE25. His most recent second-class medical certificate was issued on March 25, 2011. The copilot reported 10,701 total hours of flight time, of which, 1,120 hours were in the same make and model as the accident airplane. According to FAA records, the airplane was manufactured in 1944, and was registered to a corporation in 1999. It was a multiengine, retractable tricycle gear, monoplane that was equipped with two Curtis Wright R-2600 series radial engines. The most recent maintenance inspection in accordance with a manufacturer approved maintenance schedule was performed on July 7, 2011. At that time, the airplane had 2,220.4 hours of total time in service. The airframe maintenance records indicated that both main landing gear were replaced on December 30, 1988. The right main landing gear shock strut drag arm which fractured during the accident sequence accumulated 1,982.1 total hours of time in service. According to the maintenance records, the main landing gear was inspected on July 7, 2011 in accordance with a conditionalinspection. A part of the conditional inspection stated to, "Inspect landing gear upper trusses and brace strut assembly for condition and security." The airplane was signed off as airworthy on that date. An examination of the right main landing gear shock strut drag arm by the Safety Board Materials Laboratory revealed that a fatigue crack initiated on the exterior surface of the I-beam flange adjacent to a blend radius for an orthogonal arm. The fatigue crack initiated at numerous discrete positions on the outer I-beam surface, forming a diffuse initiation zone. A multitude of ratchet marks are present along this initiation zone. No singular defect was identified in the fatigue initiation region. ## Aircraft - Registration: [N9079Z](https://openairdocs.org/aircraft/N9079Z), registered now, S/N 44-30734, built 1944 (OpenAirDocs) - Reported make and model: NORTH AMERICAN TB-25N - Registry model: [North American TB-25N](https://openairdocs.org/model/north-american-tb-25n) (registry code 6400714) (OpenAirDocs) - Registry engine: [Wright R-2600 series](https://openairdocs.org/engine/wright-r-2600-series) (registry code 67050, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 44-30734 - Airframe hours: 2242 - Engines: WRIGHT R-2600 SER 1700 horsepower reciprocating; WRIGHT R-2600 SER 1700 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: Rag Wings & Radials Aircraft Leasing LLC - Registered owner: Rag Wings & Radials Aircraft Leasing LLC - Airworthiness certificate: Special, Limited (Special) - Last inspection: Condition, July 11, 2011 - Departed: NHK, Patuxent River, MD - Destination: GED, Georgetown, DE - Airport: GED, Sussex County Airport, runway 22, 5,000 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 63; injuries: none; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review May 23, 2011; seat: left; flight hours: 4,633 total, 1,344 in this make and model, 4,450 as pilot in command, 60 in the last 90 days, 24 in the last 30 days, 1 in the last 24 hours - Co-pilot; age 53; injuries: none; flight instructor, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review April 25, 2011; seat: right; flight hours: 10,701 total, 1,120 in this make and model, 10,480 as pilot in command, 57 in the last 90 days, 14 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 200° at 9 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 84 °F, dew point 66 °F - Altimeter: 29.86 inHg - Observed at: GED ## 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 20110904020869A](https://openairdocs.org/incident/20110904020869A), Sep 4, 2011: North American TB-25N, Georgtown, DE, Substantial damage. During landing rollout loud bang heard by flight crew, then right main landing gear collapsed. Aircraft skidded approximately 1000 feet to the right down… ## Other investigations on N9079Z (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 FTW88DPA08](https://openairdocs.org/ntsb/FTW88DPA08), Sep 19, 1988: North American TB-25N (N9079Z), Wichita Falls, TX, substantial damage ## Docket (11 files) The files NTSB released with the investigation on July 3, 2012, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=81732. 14.5 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 2.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361662&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Crew Statements (item 2, .PDF, 339 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361024&FileExtension=.PDF&FileName=Crew%20Statements-Redacted.PDF - Excerpt of Maintenance Record: Landing Gear Replacement (item 3, .PDF, 471 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361766&FileExtension=.PDF&FileName=Excerpt%20of%20Maintenance%20Record%3A%20Landing%20Gear%20Replacement-Redacted.PDF - Most Recent Maintenance Inspection (item 4, .PDF, 427 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361671&FileExtension=.PDF&FileName=Most%20Recent%20Maintenance%20Inspection-Redacted.PDF - Excerpt of North American B25 Inspection Schedule (item 5, .PDF, 79 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361767&FileExtension=.PDF&FileName=Excerpt%20of%20North%20American%20B25%20Inspection%20Schedule-Master.PDF - GED Weather Observations (item 6, .PDF, 106 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361663&FileExtension=.PDF&FileName=GED%20Weather%20Observations-Master.PDF - Materials Laboratory Factual Report 11-134 (with 6 embedded images) (item 7, .PDF, 6 photos, 818 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40359062&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2011-134%20(with%206%20embedded%20images)-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 8, .PDF, 335 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361025&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.PDF - Photo 1: View of Airplane at Rest (Courtesy of Operator) (item 9, .PDF, 2.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361664&FileExtension=.PDF&FileName=Photo%201%3A%20View%20of%20Airplane%20at%20Rest%20(Courtesy%20of%20Operator)-Master.PDF - Photo 2: View of broken right main landig gear (Courtesy of Operator) (item 10, .PDF, 2.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361665&FileExtension=.PDF&FileName=Photo%202%3A%20View%20of%20broken%20right%20main%20landig%20gear%20(Courtesy%20of%20Operator)-Master.PDF - Photo 3: View of Fracture Surface (Courtesy of FAA) (item 11, .PDF, 4.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40361666&FileExtension=.PDF&FileName=Photo%203%3A%20View%20of%20Fracture%20Surface%20(Courtesy%20of%20FAA)-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.