Revisiting Stall Speed for the Turn-Back Maneuver: Insights from Flight Tests with the EMBRAER-312 Tucano

Abstract

© 2026, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The turn-back maneuver—colloquially known as the “impossible turn”—following engine failure after takeoff remains a contentious subject in aviation safety. Often discouraged in civil operations yet critical for military contingency planning, this maneuver requires a precise understanding of aerodynamic limits. This study evaluates the stall speed dynamics during the turn-back using the EMBRAER-312 Tucano aircraft (designated T-27 in the Força Aérea Brasileira), contrasting Aircraft Flight Manual (AFM) steady-state data with flight test results obtained from high-fidelity instrumentation. The investigation highlights significant discrepancies in which AFM-derived stall speeds prove excessively conservative for the dynamic conditions of the return profile. The results confirm that stall margins are more accurately predicted using an instantaneous load factor (nza ) model, which accounts for vertical trajectory unloading. These findings challenge the reliance on static performance charts for dynamic emergency scenarios and demonstrate that, with proper technique—specifically the pitch-up entry followed by a timely nose-down transition—the maneuver can be executed at bank angles of up to 60◦ with safer margins than traditionally assumed, resolving the conflict between geometric necessity and aerodynamic safety.