Instrumented research aircraft data quality during Project SESAME ‘79 is examined in a series of tower fly-bys designed to compare temperature and static pressure measurements with reference values obtained from sensors located on the towers. Aircraft studied included an NCAR Queen Air and Sabreliner, and the South Dakota T-28. Measurements indicate that the quality of data was within acceptable limits. A discussion of data quality assessment philosophy is given, along with specific means of identifying real and potential sources of error.