The Space-Based Augmentations System (SBAS) Minimum Operational Performance Standards (MOPS) currently specifies that the message loss rate must not exceed 10-3 per message in order to meet aviation requirements for the availability of SBAS solutions. There has been little public reporting examining message loss performance in flight. The most recent published results were conducted in 1998 with the prototype version of WAAS known as the National Satellite Testbed (NSTB). Given that the capabilities and performance of WAAS have advanced beyond this prototype in its 18 years of service, a fresh analysis of the message integrity in this new system is necessary. The focus of this work is to examine the loss rate for WAAS reception using in flight data. We cross-referenced message data obtained from on-board receivers with the known broadcast history of each GEO to determine the loss rate. We mapped missed messages to timestamps along the flight path to show where messages are lost and to determine where messages are lost due to coordinated turns or low carrier-to-noise ratio (C/No). From this, we estimate the probability of message loss in nominal level flight as well as in other conditions such as turns and degraded C/No.