RV12 - Final Report - N28BS

[A2022]

reported engine trouble

https://aviation-safety.net/wikibase/347326

[A2022]

N28BS

well, if the engine is lethargic on the takeoff roll, perhaps one should abort the takeoff and find out why. after maintenance work, recommend running the engine to full power for a couple minutes on the ground to make sure it can. do you really need 2 persons onboard for an after-maintenance check flight?

https://data.ntsb.gov/carol-repgen/api/ ... 193312/pdf

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 following completion of a condition inspection, which included rebuilding both carburetors and replacement of cylinder Nos 1 and 3 ignition leads. He stated that following an uneventful pre-takeoff engine runup, he initiated takeoff on runway 31, and the airplane seemed a little “lethargic” during the takeoff roll. As the airplane was about 100 ft above ground level, the engine began to run rough and lost partial power. The pilot initiated a 180° turn to runway 13 but was “too high and too fast.” The pilot made a left turn to land on a nearby road, the airplane landed hard, and the nose wheel landing gear collapsed.

Post accident examination of the airplane revealed that the fuselage was structurally damaged. The wreckage was relocated to a secure location for further examination.

[A2022]

RV12 - Final Report - N28BS

It's unfortunate they couldn't replicate the engine malfunction to pinpoint the cause of the partial power event. Looks like it will remain a mystery.

Probable Cause and Findings
The National Transportation Safety Board determines the probable cause(s) of this accident to be:
A partial loss of engine power during initial climb for undetermined reasons.

https://data.ntsb.gov/carol-repgen/api/ ... 193312/pdf

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.