In this short paper, we illustrate the application of recently developed notions of multivariable stability margins to the analysis of vehicle flight control systems. Specifically, three designs are developed for the lateral axis dynamics of the CH- 47B helicopter, all of which satisfy classical design specifications. However, two of the designs exhibit extreme sensitivity to modeling errors that cannot be detected by measuring classical single-loop stability margins. These sensitivities are readily detected and investigated by computing the new multivariable stability margins.