Incident Overview
A pilot reported performing a normal flaps-up takeoff with full throttle. The point on the runway where the aircraft became airborne was approximately 2,800 feet from the start of the takeoff roll. The pilot climbed out at an indicated airspeed of 90 to 100 mph and engine speed of 2,400 to 2,500 rpm. The pilot then stated that the engine rpm dropped to 2,100 and subsequently to 1,900. A forced landing was executed onto a building roof top.
Performance and Certification Data
According to the aircraft's owner's manual, the calculated takeoff distance under standard conditions was less than 700 feet, indicating a significant discrepancy from the observed takeoff roll distance. Certification data indicated that at the pilot's reported climb speed of 90 to 100 mph, the geared engine should have been producing approximately 2,900 to 3,000 rpm.
Environmental Factors
A carburetor icing probability chart showed that for the ambient conditions existing at the time, with less than full power, moderate carburetor icing could result. However, a manufacturer's service instruction stated that 'the possibility of throttle icing at wide throttle openings is very remote, so remote in fact, that it can be disregarded.' The pilot had been operating at full throttle during the initial takeoff and climb, but the rpm loss occurred, suggesting a change in power setting or other factor.
Summary of Reported Events
The pilot reported no anomalies during the initial takeoff and climb until the rpm began to drop. The forced landing onto a building roof top was initiated after the loss of engine power. No further details regarding the outcome or post-incident examination were provided.