N71SNWorld Aircraft WA-3

On January 20, 2023, about 1634 central standard time, an experimental World Aircraft Company WA-3 light sport airplane, N71SN, was substantially damaged when it was involved in an accident near Shreveport, Louisiana. The pilot was not injured. The flight operated under the provisions of the Title 14 Code of Federal Regulations Part 91 as a personal flight.

The pilot reported that he departed for takeoff on runway 14 following a normal engine runup. He remained in the traffic pattern and when the airplane was on the downwind leg of the traffic pattern, abeam the numbers, the engine started to run rough and vibrate. The pilot added power and the engine smoothed out. The pilot ensured the backup electric fuel pump was in the on position and he turned the airplane to land on runway 14. While on short final, the pilot reduced power and received a low rpm warning from his avionics. When he increased the throttle, the engine stopped producing power. A high sink rate developed, and the airplane landed hard on the runway, which resulted in substantial damage to the empennage.

Postaccident examination of the airplane revealed no anomalies with the airframe or engine that would have precluded normal operation.

A review of the Carburetor Icing Probability Chart located in the FAA’s Special Airworthiness Information Bulletin CE-09-35, Carburetor Icing Prevention, dated June 30, 2009, found that the airplane was operating in an area conducive to the formation of serious icing at glide power settings and close to the area of serious icing at cruise power. The airplane was fueled with 93-octane automotive fuel which, as noted below, could make carburetor icing more likely. Additionally, the airplane was not equipped with a carburetor temperature gauge or a carburetor heat control, nor was it required to be by the FAA.

Figure 1. Carburetor Icing Probability Chart

According to Transport Canada TP 10737 (Use of Automotive Gasoline [Mogas] in Aviation), Mogas is generally higher in volatility than Avgas and will thus absorb more heat from the mixing air when vaporizing, resulting in ice accumulation at higher ambient temperatures. It goes on to say that “the likelihood of carb icing while flying on Mogas is higher,” and advises that, “[a]lthough the severity of the carb icing and the methods to deal with it are similar for both Avgas and Mogas, its ONSET is likely to occur at HIGHER AMBIENT TEMPERATURES and at LOWER HUMIDITY with Mogas. In other words, conditions under which a pilot may feel there is only a slight risk for carb icing on Avgas may in fact be ideal for the formation of ice while using more volatile Mogas. This will result in the need to select ‘carb heat on’ in less severe icing conditions and for a longer duration while using Mogas.”