Shaun,
Many manufacturers and service companies that offer computer performance programmes will calculate performance data using either AFM(DPI) or 1st Principle data. As I understand it 1st principle is the data that is used during the certification program for FAR or JAR 25, however there is a difference between the two SCAP modules and I am trying to find out exactly what the difference is. Is there an ICAO answer to this or does it vary from one manufacturer to the other?
EM