Before any aircraft type is granted a certificate of airworthiness its performance characteristics are accurately determined and, for large aircraft at least, scheduled in an approved flight manual. Superimposed on these data are certain basic performance criteria which usually limit the operational weight with altitude and temperature, and these limitations apply under all operating conditions.

In order to ensure a satisfactory level of safety for daily operation under varying conditions it is necessary to apply an operations code which takes into account other parameters such as :

(a) runway surface, gradient and length,

(b) obstructions in the take-off and landing flight paths,

(c) obstructions en route.