N5575U

On October 26, 2018, about 0730 mountain daylight time, a Piper PA-28, N5575U, was substantially damaged when it was involved in an accident near Denver, Colorado. The commercial pilot and pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot stated that he completed the preflight inspection, started the engine on the left fuel tank, then switched to the right fuel tank during taxi to the runup area. He reported a normal engine runup and recalled checking the carburetor heat and magnetos twice. He received a weather briefing, opened his flight plan, and was cleared to take off from runway 17L. He started the takeoff roll and noticed that the roll was a "little longer than normal," but attributed it to the weight of the airplane’s full fuel tanks and the passenger.

During the initial climb, the airplane was climbing at 400 to 500 ft per minute. He then noticed that the climb rate was deteriorating and that the stall warning light was flashing intermittently. He pitched down, verified that the throttle was in the full power position and that the fuel/air mixture was full rich, then applied carburetor heat and retracted the flaps. He noticed a decrease in rpm after applying carburetor heat, concluded that carburetor ice was not a factor based on “no engine roughness” before turning on carburetor heat and the atmospheric conditions, and subsequently turned the carburetor heat off. The airplane’s climb performance continued to degrade; shortly thereafter, the airplane began to descend, and the pilot performed a forced landing to a field. During the landing, the engine "seemed to lose power," then briefly surged just before touchdown.

A Federal Aviation Administration (FAA) inspector who responded to the accident site reported the airplane came to rest upright 2 miles and 195° from the departure end of runway 17L. The airplane remained intact; however, the nose and main landing gear were separated from the fuselage, the rightwing leading edge was damaged, and the empennage skin was wrinkled. One propeller blade exhibited aft bending and chordwise scratching. The inspector noted the presence of fuel in both wing tanks.

The engine crankshaft was rotated by hand, and internal and valvetrain continuity was established. Fuel was present throughout the fuel lines and was absent of any water and debris. The fuel gascolator was dry and the gascolator screen was free of debris and contamination. Power was applied to the electric fuel pump and it functioned normally. The engine-driven fuel pump was actuated by turning the propeller and it functioned normally. Both magnetos produced spark at all towers. There was no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal engine operation.

The 0653 weather reported at APA included a temperature of 3°C and a dew point of -3°C. The calculated relative humidity was about 66.8%.

According to an FAA Carburetor Icing Probability Chart, the atmospheric conditions at the time of the accident were conducive to serious icing at cruise power settings.

FAA Special Airworthiness Information Bulletin (CE-09-35) – Carburetor Icing Prevention, stated that:

…pilots should be aware that carburetor icing doesn't 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.