Optimal tiltrotor flight paths in the event of a single engine failure during short takeoff operations are investigated. A vertical plane rigid-body model is used that has as state variables aircraft position, body components of aircraft velocity, pitch angle and rate, and rotor angular speed. The control variables are the thrust coefficient of one rotor, the pilot's longitudinal stick displacement, and the nacelle angle. The model uses both parameters and aerodynamic data of the XV-15 research aircraft. The tabular aerodynamic data are interpolated with smooth functions. Tiltrotor flights after engine failure are formulated as nonlinear optimal control problems. Both continued takeoff and rejected takeoff flight after an engine failure are studied. Performance indices are selected to minimize runway length, subject to various constraints from safety considerations and tiltrotor performance limitations. These optimal control problems are parameterized via collocation into parameter optimizations for numerical solutions. Extensive numerical solutions are obtained, and sensitivity analyses are conducted to examine effects of model uncertainties