ERA24LA010 · Czech Aircraft Works Spol SRO SPORTCRUISER

Before the flight, the student pilot conducted a preflight inspection and did not notice any issues with the airplane. He then started the engine and brought it up to operating temperature, then taxied to the runway and conducted an engine runup, and all systems checked “green.” He then departed and, shortly after takeoff, the engine lost power. The student pilot then followed the engine-out procedures, glided the airplane over trees, and landed it in a vacant lot. During the landing, the left wing struck a palm tree. The airplane spun around and was substantially damaged. Examination of the dual carburetors revealed that they were in generally good condition. The 1/3-cylinder carburetor (that is, the carburetor for the Nos. 1 and 3 cylinders) had a broken or bent tube assembly for the enrichener (choke) cable. In addition, the 2/4-cylinder carburetor’s float bracket was bent and out of adjustment, the throttle valve lever was bent toward the carburetor housing, and the throttle cable was fractured near the throttle valve lever attachment. However, these findings were most likely a result of impact forces, as a fractured throttle cable would have resulted in a default condition commanding full engine power, and a bent throttle lever and deformed float bracket would have likely been observed during preflight checks in the form of improper idling or restricted throttle range. A sample of material taken from the 1/3-cylinder carburetor’s float chambers was determined to be corrosion product from oxidation of the float chamber, which was made of a zinc alloy. The oxidation likely occurred due to water-contaminated fuel left in the chamber for some time. (Unleaded automotive fuels are permitted for use in these engines with a maximum of 10% ethanol additive. Fuels blended with ethanol are susceptible to water contamination.) Dislodged pieces of corrosion deposits or excessive buildup could interfere with fuel flow through the carburetor jets which could result in a loss of engine power; however in this case, examination of the engine revealed that all eight spark plugs, the interior of the cylinder heads, spark plugs, and tops of the pistons, were heavily carbon-fouled, which was inconsistent with a loss of fuel flow and indicative of an excessively rich mixture. Carbon-fouling can hinder the spark plugs’ ability to fire effectively, leading to reduced engine performance. The student pilot advised that he had “checked” the carburetor heat during the engine runup before takeoff, as taught to him by his flight instructor. However, a review of photos taken of the cockpit after the accident revealed the carburetor heat control to have been in the On position. Application of carburetor heat during the takeoff would increase the temperature of and enrich the fuel-air mixture. Additionally, recorded engine data showed a takeoff engine rpm that was about 1,000 rpm below the maximum takeoff rpm and progressive rpm degradation that was consistent with the cumulative effects of an overly rich mixture. Review of the airplane manufacturer’s published guidance noted carburetor heat use during long descents and in areas of possible carburetor icing conditions, but did not direct that carburetor heat was to be used before or during takeoff. The loss of engine power was likely a result of the carburetor heat being on during takeoff, which enriched the mixture, reduced power output and degraded engine performance.

Verbatim NTSB analysis and probable cause from the NTSB dataset