20250426006529A

While conducting traffic pattern practice for currency, in VMC conditions and at 69.8 degrees fahrenheit and 73% humidity, while turning base to final, pilots in the citbrea experienced loss of engine power. On the second traffic pattern of the morning, the pilot on the controls observed that the aircraft descent was considerably abnormal and steep. The pilot applied increase of throttle, the engine did not respond and stayed at 400-500 RPM, and the propeller was free-spinning. Pilot in back seat assumed flight controls while the front seat pilot attempted engine re-start procedures. On final approach, pilot on controls determined that the aircraft would not make the runway and would instead crash into fence and power lines and trees. The pilot made conscious decision to turn the aircraft to the right and landed in rough, sloping terrain to avoid obstacles. Aircraft was damaged on landing with wing spar and elevator damaged, fire wall cracked, structural frame shearing at joints, and the right axle breaking off at the tire mounting. The damage to the nose section partially crushed in the airbox to the carburetor, putting the carburetor heat selector lever into a partial heating position, and making it impossible to confirm or refute if the carburetor heat selector was placed in the full hot position or not prior to the accident. Lycoming factory representative appointed by the NTSB found no equipment defects with the engine and has determined that the engine failed to produce power due to carburator icing. The temperature and the humidity levels are indicative of serious icing under glide power. Both pilot statements indicated that the carburetor heat was working during the engine run-up check and noted a decrease in engine RPM during the runup checks, but the manual does not specify a specific RPM drop to look for when conducting this check. Both pilots stated that carburetor heat was applied in each traffic pattern when they reduced power for the descent. Post-accident investigation reveals that the carburator heat was in a partially applied position, but due to the nose section damage and the denting of the carburator intake box itself, the investigation cannot determine if the carburator heat was partially or fully applied prior to the ground impact. The carburator on this aircraft did not have a carburator air temperature guage, and the pilots would not have indication of ice build up until they tried to apply power on final approach. The POH states that carburator icing is indicated if a gradual loss of RPM is noticed; "the carburetor/ alternator should be full hot as long as suspected icing conditions exist" (from POH on pg 6-7), but the pilots had manually decreased RPM for the descent and would not be able to recognize a drop in RPM brought on by carburetor icing. Without further evidence, it is determined that despite the pilot engaging carburetor heat, the carburetor still developed ice which starved the engine of oxygen to the point that it could not produce power when throttle was applied on final approach.