This paper presents a bank angle protection method for a nonlinear aircraft model. In previous study, a bank angle protection strategy was proposed based on the potential function method and tested on the linearized NASA Transport Class Model. In this paper, the potential function is modified for an improved damping performance. A switched envelope protection law is then proposed for pilot command of different magnitude to reduce the region where the envelope protection takes effect. Exponential stability of the closed-loop system with this new design is proved under some mild conditions to justify its validity. Simulation examples of bank angle protection design for NASA's nonlinear Transport Class Model are provided to verify the efficacy of the proposed design.