# NTSB ERA18LA270: Maule M7, N969AW, Floresville, TX, September 11, 2018 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: September 11, 2018, 16:37 local (21:37 UTC) - Place: Floresville, TX - Coordinates: 29.129722, -98.75 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=29.1297&lon=-98.7500&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 April 20, 2020 - Report: Approved by Office Director - NTSB office: Eastern Region Aviation - Parties: FAA/FSDO - NTSB case key (mKey): 98458 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA18LA270 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/98458/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=98458 - Page: https://openairdocs.org/ntsb/ERA18LA270 ## Probable cause The separation of the left inboard main landing gear (MLG) attachment bolt due to insufficient torque, which resulted in the collapse of the left MLG. ## 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 · Incorrect service/maintenance (probable cause); cases with it: [Maule M-7-235C, 2 cases](https://openairdocs.org/ntsb-findings/01023211/cases.md?model=5460110), [All aircraft, 66 cases](https://openairdocs.org/ntsb-findings/01023211/cases.md) - [Maintenance/inspections: scheduled maint checks](https://openairdocs.org/ntsb-findings/01010520): Aircraft › Aircraft handling/service · Related maintenance info; cases with it: [Maule M-7-235C, 1 case](https://openairdocs.org/ntsb-findings/01010520/cases.md?model=5460110), [All aircraft, 76 cases](https://openairdocs.org/ntsb-findings/01010520/cases.md) - [Maintenance: scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010): Personnel issues › Task performance · Other; cases with it: [Maule M-7-235C, 1 case](https://openairdocs.org/ntsb-findings/02062010/cases.md?model=5460110), [All aircraft, 320 cases](https://openairdocs.org/ntsb-findings/02062010/cases.md) - [Use of equip/info: use of available resources](https://openairdocs.org/ntsb-findings/02063035): Personnel issues › Task performance · Other; cases with it: [Maule M-7-235C, 1 case](https://openairdocs.org/ntsb-findings/02063035/cases.md?model=5460110), [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: [Maule M-7-235C, 1 case](https://openairdocs.org/ntsb-events/040/sequence.md?model=5460110), [All aircraft, 484 cases](https://openairdocs.org/ntsb-events/040/sequence.md) - [Landing-landing roll: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338); cases with it: [Maule M-7-235C, 1 case](https://openairdocs.org/ntsb-events/338/sequence.md?model=5460110), [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) - [Landing-landing roll: Landing gear collapse](https://openairdocs.org/ntsb-events/094) (defining event); cases with it: [Maule M-7-235C, 2 cases](https://openairdocs.org/ntsb-events/094/sequence.md?model=5460110), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) ## Analysis The flight instructor and the private pilot-rated student, who was in the left seat and was also the airplane owner, were practicing approaches. Upon landing, the pilots heard a loud popping noise, and the instructor then initiated a go-around. Subsequently, the pilot felt vibration under the floorboard. The pilots thought that a tire might have blown. The instructor flew the approach and conducted a three-point landing, and just before the airplane came to a stop, the left main landing gear (MLG) collapsed, which resulted in substantial damage to the left wing. An examination of the left MLG revealed that its inboard attachment bolt and nut were missing. After the accident, the bolt was found along the path of the landing rollout. Examination of the attachment bolt revealed that the bolt threads were undamaged. The attachment nut was not found. The right MLG's inboard attachment bolt and nut were found still attached; however, they were loose, with only two to three threads visible past the nut. The inboard attachment bolts were upgraded high-strength bolts. The airframe manufacturer had issued a service letter (SL) that stated that, when using the high-strength bolts, the outboard attachment bolts required the same amount of torque as indicated in the airplane maintenance manual but that the inboard attachment bolts required a higher torque amount than the standard bolts. However, a review of the maintenance manual revealed that it did not include the new, higher torque requirements specified in the SL. Therefore, mechanics who only follow the maintenance manual may not be aware that higher torque values are required. A review of the airplane maintenance records revealed that its last annual inspection was completed about 6 months before the accident. The mechanic who performed the inspection reported that he did not verify the torque on the bolts, that he only used his hands to confirm that they were secure, and that he did not reference the SL during the inspection. It could not be determined whether the mechanic's failure to verify the torque on the bolts or the insufficient torque values in the MM led to the torque on the left inboard MLG attachment bolt being insufficient and the resultant collapse of the left MLG. ## Factual narrative On September 11, 2018, about 1637 central daylight time, a Maule M-7-235C, N969AW, was substantially damaged after the left, main landing gear collapsed at a private, grass airstrip near Floresville, Texas. The flight instructor and a private pilot-rated student were not injured. The airplane was operated by an individual under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that originated at Floresville about 1600.According to an inspector with the Federal Aviation Administration (FAA), the flight instructor and his student were practicing approaches. Upon landing, the pilots heard a loud popping noise, and the flight instructor performed a go-around. The student in the left seat could feel vibration under the floor board. Suspecting a blown tire, the pilots discussed how the airplane might handle during the next landing. The instructor flew the approach and landing. After a normal 3-point landing, and just before the airplane came to a stop, the left main landing gear collapsed. The FAA inspector responded to the accident site and examined the wreckage. He reported that the left wing sustained structural damage during the landing. The propeller struck the ground after the gear collapsed. The inspector observed that the left main landing gear inboard attachment bolt was missing. The bolt was later found along the path of the landing rollout. The bolt threads were undamaged, and the attaching nut was not located. The right inboard attachment bolt and nut were still attached; however, they were untorqued and loose, with only 2-3 threads visible past the nut. The 100-hr/annual inspection procedures in the M7-235C Maintenance Manual (MM) stated that, under the main landing gear inspection procedures, "The torque on the inboard attach bolts must be 240-300 inch pounds and on outboard clamp bolts 160-190 inch pounds." The airplane was fitted with upgraded high strength attach bolts. Maule Service Letter (SL) No. 66, revision B, dated May 2, 2006, addressed the installation of the high strength bolts. According to the SL, the torque for the outboard clamp bolts was the same as the MM inspection guide (160-190 inch pounds); however, the torque for the inboard attach bolts increased to 450-500 inch pounds. Service Letter No. 66 also stated, "Retorque bolts after 25 hours and per Maintenance Manual thereafter." The MM did not incorporate the new torque requirements for the inboard bolts. Following the MM only, this allowed the inboard bolts to be torqued to 240-300 inch pounds, or about 200 inch pounds lower than the requirement in SL No. 66. A review of the aircraft maintenance records revealed that the most recent annual inspection was completed in April, 2018. The mechanic who performed the inspection reported that he did not retorque the attachment bolts; he checked them by feeling them with his hands only. He did notreference SL No. 66 during the annual inspection. ## Aircraft - Registration: [N969AW](https://openairdocs.org/aircraft/N969AW), registered now, S/N 25093C (OpenAirDocs) - Reported make and model: Maule M7 (235C) - Registry model: [Maule M-7-235C](https://openairdocs.org/model/maule-m-7-235c) (registry code 5460110) (OpenAirDocs) - Category: Airplane - Serial number: 25093C - Year built: 2003 - Airframe hours: 1975 - Engines: Lycoming IO-540 Series 235 hp reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, April 30, 2018 - Departed: N/A, Floresville, TX - Destination: N/A, Floresville, TX - Airport: N/A, Private - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 31; injuries: none; flight instructor, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; seat: right; flight hours: 5,100 total - Student pilot; age 51; injuries: none; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, without waivers/limitations; seat: left; flight hours: 515 total ## Weather - Conditions: Visual (VMC), Day - Wind: 360° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: 5,500 ft broken - Temperature: 82 °F, dew point 70 °F - Altimeter: 29.87 inHg - Observed at: SSF, 20 nm away ## 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 20180911019079A](https://openairdocs.org/incident/20180911019079A), Sep 11, 2018: Maule M-7-235C, Floresville, TX, Substantial damage. Certified flight instructor (CFI) , and pilot seeking an instrument rating (owner) were practicing IFR approaches. The aircraft is equipped with alaskan bush… ## Docket (6 files) The files NTSB released with the investigation on October 28, 2019, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=98458. 1.9 MB in all. - FAA Inspector's Statement (item 1, .PDF, 47 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40477201&FileExtension=.PDF&FileName=FAA%20Inspector%27s%20Statement-Master.PDF - Correspondence with FAA (item 2, .PDF, 502 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40477202&FileExtension=.PDF&FileName=Correspondence%20with%20FAA-Master.PDF - NTSB Memorandum for Record - Peeler (item 3, .PDF, 110 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40477203&FileExtension=.PDF&FileName=NTSB%20Memorandum%20for%20Record%20-%20Peeler-Master.PDF - Excerpt - Maule M7 Maintenance Manual (item 4, .PDF, 406 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40477204&FileExtension=.PDF&FileName=Excerpt%20-%20Maule%20M7%20Maintenance%20Manual-Master.PDF - Maule Service Letter No. 66 (item 5, .PDF, 365 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40477205&FileExtension=.PDF&FileName=Maule%20Service%20Letter%20No.%2066-Master.PDF - Photo Array (item 6, .PDF, 5 photos, 484 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40477206&FileExtension=.PDF&FileName=Photo%20Array-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.