INTRODUCTION (Note: In this Data Item@ data options and facilities which are not available in the current release of the program are presented in italic script.) Descriptive error and warning messages are produced by the Pre-Processor (APP_01) and by the Flight Performance Program (APP_02) when an error is found in the input data or during calculation of the aircraft performance. Some of the Flight Performance Program messages also occur when the Interpolation Program (APP_03) is used because it uses the same table input (which includes syntax checking) and interpolation routines as the Flight Performance Program. This Data Item contains more complete descriptions of the errors encountered than is given in the output error messages.