What happened
On June 7, 2014, a Piper PA-28-140, registration PT-IZV, was conducting a local flight training mission departing from Campo de Marte Airport in São Paulo. Approximately 35 minutes into the flight, while performing a descent maneuver, the crew encountered significant difficulty regaining level flight and increasing engine power.
Unable to maintain altitude, the crew performed an emergency landing on a bridge spanning the SP-23 highway in Mairiporã, São Paulo. During the landing roll, the aircraft collided with a truck. The impact resulted in substantial damage to the landing gear, wings, and the lower fuselage. Both occupants of the aircraft, the instructor and the student, escaped the incident without injury.
The investigation
CENIPA investigators examined the aircraft's engine and control systems at an ANAC-certified maintenance facility. The investigation focused on the instructor's report that the throttle lever felt rigid in the reduced power position, preventing acceleration. Post-accident inspections of the throttle mechanism, magnetos, spark plugs, and carburetor revealed no mechanical obstructions, foreign object damage, or functional abnormalities. All components were found to be operating within normal parameters.
Investigators also analyzed meteorological data from Campo de Marte Airport. The temperature and dew point recorded during the flight indicated high relative humidity. When plotted on a carburetor icing probability chart, the conditions were classified as "Serious icing – descent power," suggesting that ice formation could have occurred during the descent maneuver. The investigators noted that while ice could explain the reported stiffness in the throttle, such ice would likely dissipate shortly after the cause is removed, making it difficult to detect during post-crash inspections.
Findings
- The crew failed to activate the carburetor heat during the descent.
- Environmental conditions were conducive to carburetor icing.
- The pilot's decision-making and oversight regarding engine heat management contributed to the loss of power.