The paper discusses a hidden aspect of a firm's capital structure through the use of a real options application. It is applied to the US airline industry, characterized by over levered balance sheets, and one which on some estimates, has made zero cumulative profit taking the years of the last century together. The paper introduces the notion of "financial flexibility", defined as the freedom (or flexibility) enjoyed by a conservatively geared firm to respond quickly and secure positive NPV projects, as opposed to an over levered firm. This "flexibility" is then valued as a real option using a model based on arithmetic Brownian motion involving a path dependant option pricing framework. It analyses the implications of debt financing in the ...