# NTSB CEN16LA273: Brandt Sonex, N393SX, Lodi, WI, July 19, 2016 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 18, 2016, 19:15 local (Jul 19, 2016, 00:15 UTC) - Place: Lodi, WI - Coordinates: 43.333332, -89.520835 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.3333&lon=-89.5208&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report May 23, 2017 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 93635 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN16LA273 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/93635/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=93635 - Page: https://openairdocs.org/ntsb/CEN16LA273 ## Probable cause The separated rocker arm assembly for undetermined reasons, which resulted in the partial loss of engine power and led to the landing gear collapsing during the subsequent forced landing. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Brandt Leroy E SONEX, 1 case](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=05633MY), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Owner/builder; cases with it: [Brandt Leroy E SONEX, 1 case](https://openairdocs.org/ntsb-findings/02062035/cases.md?model=05633MY), [All aircraft, 371 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md) - [Maintenance: fabrication](https://openairdocs.org/ntsb-findings/02062025): Personnel issues › Task performance · Other; cases with it: [Brandt Leroy E SONEX, 1 case](https://openairdocs.org/ntsb-findings/02062025/cases.md?model=05633MY), [All aircraft, 30 cases](https://openairdocs.org/ntsb-findings/02062025/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: [Brandt Leroy E SONEX, 1 case](https://openairdocs.org/ntsb-events/040/sequence.md?model=05633MY), [All aircraft, 484 cases](https://openairdocs.org/ntsb-events/040/sequence.md) - [Enroute: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340); cases with it: [Brandt Leroy E SONEX, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=05633MY), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Enroute: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Brandt Leroy E SONEX, 1 case](https://openairdocs.org/ntsb-events/342/sequence.md?model=05633MY), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Brandt Leroy E SONEX, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=05633MY), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Collision during takeoff/land](https://openairdocs.org/ntsb-events/490); cases with it: [Brandt Leroy E SONEX, 2 cases](https://openairdocs.org/ntsb-events/490/sequence.md?model=05633MY), [All aircraft, 1,309 cases](https://openairdocs.org/ntsb-events/490/sequence.md) ## Analysis During a local flight, the pilot of an experimental amateur-built airplane had a partial engine power loss. He said that the engine sounded different but remained running. He turned the airplane back to the airport and noted he was high and fast. He indicated that he bled off airspeed, as he wanted to avoid buildings before landing. He subsequently reduced power and performed a landing with calm wind present. The airplane's nose and left main landing gear collapsed after touchdown, the airplane skidded to the north side of the runway, and exited the runway into a ditch where it sustained the substantial damage. The airplane was powered by an engine that the pilot/builder assembled from a kit. The airplane accumulated 25 hours of flight time at the time of the accident. The kit manufacturer engine assembly and installation manual had specific rocker shaft instructions that included procedures on how to adjust and install rocker arms. An examination revealed that the threaded shaft of a rocker arm swivel pad had separated at a point on the shaft where there was a cross drilled hole. The remaining rocker arms did not exhibit the appearance of arm adjustment in accordance with the kit manufacturer's assembly manual. Detailed examination of the failed valve adjuster showed it separated into two portions approximately mid length in the shank area between the two threaded areas. This location was coincident with a hole drilled crosswise through the shank of the valve adjuster. The fracture surfaces exhibited crack arrest patterns consistent with a fatigue fracture. The origin of the fatigue fracture appears to be coincident with the edge of the cross-drilled hole. Examination of the exemplar valve adjuster and specifically the cross-drilled hole revealed a roughly finished surface with a pronounced burr around the circumference of the hole. A professional materials engineering publication, in part, stated, "The fatigue strength of components can be reduced merely by the presence of a drilled hole; it is further reduced by failure to remove burrs (incurred during drilling) from the hole edges. Fractures originating at drilled holes are common in complex parts containing internal, intersecting machined passages because of the difficulty and expense of providing adequate break-edge radii at such locations. It could not be determined if the failure of the rocker arm was due to the misassembly of the rocker arm assembly and/or the toolmarks left by the manufacturing process. ## Factual narrative On July 18, 2016, about 1915 central daylight time, a Brandt Sonex experimental amateur-built airplane, N393SX, impacted a ditch when it exited runway 9 (1,875 feet by 105 feet, turf) at the Lodi Lakeland Airport (9WN5), near Lodi, Wisconsin, during a forced landing following a partial loss of engine power. The sport pilot was uninjured. The airplane fuselage was substantially damaged during the impact with the ditch. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Day visual meteorological conditions prevailed for the flight, which operated without a flight plan. The local flight originated from 9WN5 at time unknown.The pilot reported a partial loss of engine power, which occurred northwest of 9WN5. He said that the engine sounded different but remained running. He turned the airplane back to the airport and noted he was high and fast. He indicated that he bled off airspeed, as he wanted to avoid buildings before landing. He subsequently reduced power and performed a landing. The airplane's nose and left main landing gear collapsed after touchdown, the airplane skidded to the north side of the runway, and exited the runway into a ditch where it sustained the substantial damage. The pilot, age 71, held a Federal Aviation Administration (FAA) sport pilot certificate and he reported that he accumulated 180 hours of total flight time. N393SX was a low-wing, fixed tricycle gear, 2-seat, experimental amateur-built airplane with serial number 393. It was powered by a 70-horsepower AeroVee engine driving a fixed pitch Sensenich propeller. The pilot reported that the airplane had a condition inspection completed on December 4, 2015, and that the airplane accumulated 25 hours of flight time at the time of the accident. The airplane and engine were sold as kits that the owner assembled. The kit manufacturer engine assembly and installation manual had specific rocker shaft instructions that included procedures on how to adjust and install rocker arms. At 1953, the recorded weather at the Dane County Regional Airport-Truax Field, near Madison, Wisconsin, was: Wind calm; visibility 10 statute miles; sky condition few clouds at 5,500 feet; temperature 27 degrees C; dew point 17 degrees C; altimeter 30.15 inches of mercury. An FAA inspector examined the wreckage and observed that the threaded shaft of a rocker arm swivel pad on the rocker arm assembly had separated at a point on the shaft where there was a cross drilled hole. The accident engine's remaining rocker arm assemblies did not exhibit the appearance of arm assembly adjustment in accordance with the adjustment directions in the kit manufacturer's assembly manual. The separated rocker arm swivel pad and an exemplar pad from the accident engine were shipped to the National Transportation Safety Board (NTSB) Materials Laboratory for detailed examination. An NTSB Materials Laboratory Engineer examined the itemsand produced Materials Laboratory Factual Report No. 16-101, which is appended to the docket material associated with this investigation. The report, in part, indicated the failed valve adjuster separated into two portions approximately mid length in the shank area between the two threaded areas. This location was coincident with a hole drilled crosswise through the shank of the valve adjuster. The fracture surfaces exhibited crack arrest patterns consistent with a fatigue fracture. The origin of the fatigue fracture appears to be coincident with the edge of the cross-drilled hole. The ball bearing on the end of the valve adjuster had seized in place and could not be rotated. A measurement of the hardness on a section of the fractured valve adjuster revealed a hardness of 20.2 on the Rockwell C scale. Examination of the exemplar valve adjuster and specifically the cross-drilled hole revealed a roughly finished surface with a pronounced burr around the circumference of the hole. ASM International Handbook, Volume 11, Failure Analysis and Prevention, in part, stated: The fatigue strength of components can be reduced merely by the presence of a drilled hole; it is further reduced by failure to remove burrs (incurred during drilling) from the hole edges. Fractures originating at drilled holes are common in complex parts containing internal, intersecting machined passages because of the difficulty and expense of providing adequate break-edge radii at such locations. ## Aircraft - Registration: [N393SX](https://openairdocs.org/deregistered/N393SX-2020-03-06), registration cancelled 2020-03-06, S/N 393, built 2014 (OpenAirDocs) - Reported make and model: BRANDT SONEX - Registry model: [Brandt Leroy E SONEX](https://openairdocs.org/model/brandt-leroy-e-sonex) (registry code 05633MY) (OpenAirDocs) - Registry engine: [Aerovee 2.1](https://openairdocs.org/engine/aerovee-2-1) (registry code 01402, 4 cycle) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 393 - Airframe hours: 25 - Engines: Aerovee 70 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, December 4, 2015 - Departed: 9WN5, Lodi, WI - Destination: 9WN5, Lodi, WI - Airport: 9WN5, Lodi Lakeland, runway 09, 1,875 × 105 ft, grass/turf ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 71; injuries: none; sport pilot; airplane ratings: single-engine land; medical: sport pilot; last flight review October 30, 2015; restraint: 3-point; flight hours: 180 total, 180 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Temperature: 81 °F, dew point 63 °F - Altimeter: 30.14 inHg - Observed at: KMSN, 14 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 20160718011239A](https://openairdocs.org/incident/20160718011239A), Jul 18, 2016: Brandt Leroy E SONEX, Lodi, WI, Substantial damage. On July 18, 2016, at 1915 CDT a Sonex, N393SX, made an emergency landing at 9WN5 following a partial power loss. After touchdown the nose gear collapsed… ## Other investigations on N393SX (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 CEN19LA045](https://openairdocs.org/ntsb/CEN19LA045), Dec 15, 2018: Brandt Sonex (N393SX), Lodi, WI, substantial damage. Probable cause: The pilot's failure to maintain proper alignment with the runway during final approach, which resulted in impact with a tree. ## Docket (6 files) The files NTSB released with the investigation on March 29, 2017, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=93635. 8.3 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 897 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450444&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Photos - FAA Supplied Images (item 2, .PDF, 697 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450445&FileExtension=.PDF&FileName=Photos%20-%20FAA%20Supplied%20Images-Master.PDF - Materials Laboratory - Report No. 16-101 (item 3, .PDF, 4.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450448&FileExtension=.PDF&FileName=Materials%20Laboratory%20-%20Report%20No.%2016-101-Master.PDF - Miscellaneous Information - ASM Volume 11 Reference Excerpt (item 4, .PDF, 2.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450447&FileExtension=.PDF&FileName=Miscellaneous%20Information%20-%20ASM%20Volume%2011%20Reference%20Excerpt-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 5, .PDF, 147 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450450&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Master.PDF - Evidence Control Form (item 6, .PDF, 182 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450451&FileExtension=.PDF&FileName=Evidence%20Control%20Form-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.