What is the difference between “Unknown” and a null value in the Bureau or Serial Number dimension element?
A null value implies that the data was not reported against a specific Aircraft (TEC’s beginning with “A, K, or N”) or Engine TEC (TEC’s beginning with “J, R, or T”). “Unknown” denotes that the data was reported against a specific Aircraft or Engine TEC, but that the Bureau Number or Serial Number reported was not valid (for Aircraft a valid Bureau Number is based on a range of values from AIRRS; for Engines any numeric value is considered valid).
