N504JN

On November 9, 2024, at 1903 eastern standard time, a Schweizer 269 C-1 helicopter, N504JN, was substantially damaged when it was involved in an accident near Boalsburg, Pennsylvania. The private pilot and passenger were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot, he departed and initiated a slow climb to clear a mountain. The pilot reported that, based on the temperature, dew point, and humidity, he applied carburetor heat; the helicopter's icing gauge also indicated the need for carburetor heat. The pilot slightly leaned the fuel mixture while maintaining full power for the climb. As the helicopter approached the mountain, the pilot increased the throttle and raised the collective. The pilot then heard an unfamiliar noise from the engine, followed by a noticeable loss of power. The rotor gauge did not reach the upper end of the scale, prompting the pilot to reduce collective and apply additional throttle, which resulted in an engine backfire.

With insufficient power to clear the mountain, the pilot executed a right turn toward lower terrain. The engine continued to produce power, but was insufficient to sustain flight. Concerned about a potential total loss of engine power, the pilot initiated a descent toward a nearby farm field, but due to uneven terrain, the pilot chose to land on a paved road in a housing development. While maintaining a controlled descent, the pilot attempted to apply power upon reaching a cul-de-sac, but received no response from the engine. The helicopter subsequently landed hard from a height of about 4 feet, and the tail rotor impacted an embankment on the lower side of the cul-de-sac.

During a postaccident engine run, the engine operated without any notable anomalies, including smoke or abnormal sounds. At 1,400 to 1,500 rpm, magneto checks were performed, and the engine continued to operate normally in the left, right, and both magneto positions. Carburetor heat activation resulted in the expected rpm change, and when the mixture was pulled to idle cut-off, the engine exhibited a normal rpm increase before shutting down. The engine run revealed no anomalies that would have precluded normal operation of the engine.

The recorded temperature and dew point near the accident site was about 43°F and 25°F, respectively. On a carburetor icing probability chart, those temperatures were in the “icing – glide and cruise power” range. The pilot stated that he applied carburetor heat before the loss of engine power.

According to FAA Special Airworthiness Information Bulletin CE-09-35 (Carburetor Ice Prevention), pilots should be aware that carburetor icing does not just occur in freezing conditions: it can occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. Icing can occur in the carburetor at temperatures above freezing because vaporization of fuel, combined with the expansion of air as it flows through the carburetor (Venturi effect), causes sudden cooling, sometimes by a significant amount within a fraction of a second. Carburetor ice can be detected by a drop in rpm in fixed pitch propeller airplanes and a drop in manifold pressure in constant speed propeller airplanes. In both types, usually there will be a roughness in engine operation.