A method of calculating a system level air data parameter for an aircraft, for example aircraft angle-of-attack (AOA) and/or angle-of-sideslip (AOS), includes measuring a plurality of local static pressures pi. Next, a plurality of non-dimensional pressure ratios are each generated as a function of one of the plurality of local static pressures pi, a predicted system static pressure Pspredicted, and a predicted impact pressure qc predicted. Then, the system level air data parameter is calculated as a function of the generated plurality of non-dimensional pressure ratios. Air data systems having air data computers configured to implement the method are also disclosed. The air data systems can be Flush Air Data Systems (FADS), or other types of air data systems.