The purpose of this research was to investigate a method of determining an aircraft's velocity in the event of total air data system failure. The process combined GPS aided inertial velocity with a continuously estimated wind velocity. A velocity estimator (VEST) algorithm was developed to combine the inertial and wind velocities to provide an estimate of the aircraft's current true velocity to be used for command path gain scheduling and for display in the cockpit. The culmination of this effort resulted in a flight test program as part of a Test Management Project at the United States Air Force Test Pilot School. The project consisted of two ground test and six flight test evaluation sorties. The average true airspeed from the estimator algorithm during inflight maneuvers was determined to be 12 knots, non-divergent, and minimally variable. The research identified the potential of the algorithm to determine an aircraft's airspeed in the event of an air data system failure.