The Federal Aviation Administration is developing new design procedures for extending airport pavement life beyond 20 years based on the concept of serviceability: the measure of a how well a pavement fulfills user expectations. A key element is a new distress “mega-index” whose elements are intended to represent the independent components of airport pavement serviceability: low foreign object damage potential, low skid potential, and smoothness. This research verifies the assumption that these three components completely describe airport pavement serviceability and proposes an improved probability-based form for the mega-index. The new form has several anticipated advantages including a real-world meaning, the expectation that it can be integrated into a risk management system, and the ability to break down condition into multiple submodels with separate inputs to improve the accuracy of pavement condition predictions.