# NTSB WPR24LA023: Vans RV-12, N28BS, Novato, CA, October 26, 2023 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: October 26, 2023, 13:30 local (20:30 UTC) - Place: Novato, CA - Coordinates: 38.14904, -122.56179 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=38.1490&lon=-122.5618&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Unknown or undetermined](https://openairdocs.org/ntsb-events/000) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report October 22, 2025 - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration, Rotech - NTSB case key (mKey): 193312 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR24LA023 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193312/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=193312 - Page: https://openairdocs.org/ntsb/WPR24LA023 ## Probable cause A partial loss of engine power during initial climb for undetermined reasons. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Aircraft](https://openairdocs.org/ntsb-findings/01050000): Aircraft › Aircraft power plant · Unknown/Not determined (probable cause); cases with it: [Vans RV-12, 1 case](https://openairdocs.org/ntsb-findings/01050000/cases.md?model=0690009), [All aircraft, 151 cases](https://openairdocs.org/ntsb-findings/01050000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Initial climb: Unknown or undetermined](https://openairdocs.org/ntsb-events/000) (defining event); cases with it: [Vans RV-12, 1 case](https://openairdocs.org/ntsb-events/000/sequence.md?model=0690009), [All aircraft, 1,703 cases](https://openairdocs.org/ntsb-events/000/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Vans RV-12, 2 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=0690009), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Hard landing](https://openairdocs.org/ntsb-events/092); cases with it: [Vans RV-12, 2 cases](https://openairdocs.org/ntsb-events/092/sequence.md?model=0690009), [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis The accident flight was the airplane’s first flight since receiving maintenance that included a condition inspection and the rebuilding of both carburetors. The pilot reported that, following an uneventful engine run-up, he initiated takeoff. During the takeoff roll, the airplane seemed a little “lethargic” and, when the airplane was about 100 ft above ground level, the engine began to run rough and lost partial power. He initiated a 180° turn to the departing runway; however, the airplane was “too high and too fast” to land on runway, and he made a left turn to a nearby road. The airplane landed hard, and the nosewheel landing gear collapsed. Review of the downloaded data from the airplane’s avionics showed that, during the takeoff sequence, the engine rpm decreased from 5,000 rpm to about 3,200 rpm, along with a corresponding decrease in the exhaust gas temperatures for the Nos. 1 and 3 cylinders. At the time of the rpm decrease, the fuel pressure and fuel flow remained within factory specifications. Postaccident examination of the recovered airframe and engine revealed no evidence of a preexisting mechanical anomaly that would have precluded normal operation. The mixture control was found about one turn out from full rich, and a carburetor float bowl vent line was found disconnected from the carburetor for the Nos. 1 and 3 cylinders. A functional test conducted using a similar airplane and engine equipped with a similar fuel mixture system with the float vent line disconnected could not replicate the partial loss of engine power. The test airplane’s engine ran normally, and no change in engine performance was observed with manipulation of the mixture knob from full rich to lean. ## Factual narrative On October 26, 2023, about 1330 Pacific daylight time, an experimental amateur-built Vans RV-12, N28BS, was substantially damaged when it was involved in an accident near Novato, California. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, the accident flight was the first flight since receiving maintenance that included a condition inspection, the rebuilding of both carburetors, and the replacement of the Nos. 1 and 3 cylinders’ ignition leads. He stated that, following an uneventful pretakeoff engine run-up, he initiated takeoff on runway 31, and the airplane seemed a little “lethargic” during the takeoff roll. When the airplane was about 100 ft above ground level, the engine began to run rough and lost partial power. The pilot stated he initiated a 180° turn, but the airplane was “too high and too fast” to land on runway 13, so he made a left turn to a nearby road. The airplane landed hard on the road, and the nosewheel landing gear collapsed. Postaccident examination of the airplane revealed that the fuselage was structurally damaged. The airplane was equipped with a Dynon FlightDek D180 display unit that recorded various engine parameters, including rpm, exhaust gas temperature, fuel pressure, and fuel flow. Review of the downloaded data showed that, during the takeoff sequence, engine rpm decreased from 5,000 rpm to about 3,200 rpm, and the exhaust gas temperatures for the Nos. 1 and 3 cylinders decreased from about 1,350° F to about 350 to 500° F. At the time of the decreased rpm, fuel pressure was 2.3125 psi, and fuel flow was 5.625 gallons per hour. According to the Pilot Operating Handbook for the Vans RV-12, fuel pressure limits were from 2.2 to 5.8 or 7.2 psi, depending on what engine-driven fuel pump was installed. The airplane was equipped with an Aircraft Service in-flight mixture control system that was nonstandard for the Rotax engine. Examination of the recovered airframe revealed that the mixture control knob in the cockpit was found one turn out from full rich. The engine remained attached to the airframe, and all accessories remained attached. The carburetor vent lines extended from the firewall to a “T” connector, then to each carburetor. All fuel lines remained secured to their respective fittings, except the carburetor float chamber vent line was found disconnected from the carburetor for the Nos. 1 and 3 cylinders. The mixture system jet was found free of obstructions. Rotational continuity was established throughout the engine and valvetrain, and thumb compression was obtained on all four cylinders. Compressed air was applied to the engine fuel inlet lines, and no obstructions were found throughout the fuel system. The fuel cap vent was free of obstructions. Both carburetors were removed and partially disassembled. Both carburetor slides were free to move up and down, and the floats were intact. According to themechanic who rebuilt the carburetors before the accident flight, the mixture control system would enable the pilot to lean the engine to obtain 100-200 rpm with a turn or two of the mixture control knob but that he advocates to use the mixture control only at altitudes higher than 4,000 ft. He stated that, at two turns out, the exhaust gas temperatures will rise but remain within limits. He stated that, if the pilot leans it beyond two turns, the engine will develop roughness but not a loss of engine power. The mechanic performed an engine runup test on his own airplane, which was equipped with the same engine and mixture system. He reported that there was a negligible effect of running the engine through a simulated 5-minute climb with the carburetor float chamber vent line disconnected from the carburetor for the Nos. 1 and 3 cylinders. He stated that operating the mixture control knob through its full travel had an insignificant effect on operation of the engine, which felt and sounded normal throughout the test. ## Aircraft - Registration: [N28BS](https://openairdocs.org/aircraft/N28BS), registered now, S/N 120002 (OpenAirDocs) - Reported make and model: VANS AIRCRAFT INC RV-12 - Registry model: [Vans RV-12](https://openairdocs.org/model/vans-rv-12) (registry code 0690009) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 120002 - Airframe hours: 1414.1 - Engines: Rotax 912ULS 100 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Blue Side Up Aviation Group - Airworthiness certificate: Special, Experimental (Special); Special, Experimental light sport (Special) - Last inspection: Condition, October 12, 2023, 0 hours before - Airport: DVO, Gnoss Field, runway 13, 3,303 × 75 ft, asphalt - Equipment: Electronic primary flight display ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 83; injuries: none; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: sport pilot; seat: left ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 66 °F, dew point 34 °F - Altimeter: 30.10 inHg - Observed at: KDVO, 1 nm away - METAR: KDVO 262035Z AUTO 00000KT 10SM CLR 19/01 A3010 RMK AO2 PWINO ## 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 20231026020709A](https://openairdocs.org/incident/20231026020709A), Oct 26, 2023: Vans Aircraft Inc RV-12, Novato, CA, Substantial damage. This was the aircraft's first flight since conditional inspection and carberator maintenance. Both carbs on aircraft engine were rebuilt and a run up was… ## Docket (10 files) The files NTSB released with the investigation on October 22, 2025, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=193312. 175 MB in all. - Memorandum of record - pilot (item 1, PDF, 1 page, 72 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354634&FileExtension=pdf&FileName=roc%20pilot-Rel.pdf - Memorandum of record - mechanic (item 2, PDF, 1 page, 78 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354427&FileExtension=pdf&FileName=roc%20mechanic-Rel.pdf - NTSB airframe and engine examination summary (item 3, PDF, 3 pages, 98 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354749&FileExtension=pdf&FileName=Airframe%20and%20Engine%20Exam%20Summary-Rel.pdf - Pages from the pilot operating handbook (item 4, PDF, 2 pages, 77 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354389&FileExtension=pdf&FileName=Pages%20from%20RV12%20POH%20Rev%2019-Rel.pdf - Mixture system description (item 5, PDF, 2 pages, 357 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354644&FileExtension=pdf&FileName=Mixture%20contol%20description%20%26%20operation%20Issue%204-Rel.pdf - Mechanic provided test writeup (item 6, PDF, 1 page, 47 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354437&FileExtension=pdf&FileName=Disconected%20Mixture%20Test_Redacted-Rel.pdf - Mechanic provided test video (item 7, MOV, 152 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354759&FileExtension=mov&FileName=Test%20Mixture%20tube%20disconnect-Rel.mov - Release of aircraft wreckage, NTSB form 6120.15 (item 8, PDF, 1 page, 199 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354399&FileExtension=pdf&FileName=wreckage_release%20final_Redacted-Rel.pdf - Dynon flight dek D180 data (item 9, CSV, 20.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354654&FileExtension=csv&FileName=FlightDEK-D180_sn2348_20250708_datalog-Rel.csv - Investigation photographs (item 10, PDF, 5 pages, 4 photos, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19354664&FileExtension=pdf&FileName=Investigation%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.