Princess PP, Performance A refers to the schedule of aeroplanes in Group A. This effectively means that in essence, should a failure of the most critical engine occur, a forced landing should not be necessary. In order that this criteria may be met, calcualtions have to be made in order to establish what weight the aeroplane may safely (and legally) lift off the ground, and still clear a 35' screen height at the end of the take off distance available. Naturally, weather and other conditions will affect the "lifting capacity" of the wing, and weight may need to be reduced accordingly. The calculations will also resolve the speeds at which go/no-go decisions are made, and rotation speed/safe climb speed. In days of old, when Pontious was a pilot, these calculations were made manually using graphs/and-or tables, but as in all things the computer does much of the number crunching these days.
Other performance schedules exist, such as groups B,C, E etc, and these lesser groups are more likely to need to land following the failure of the most critical engine.
Hope that helps.
Tailwinds.....
