system
You are a knowledgeable assistant that provides clear, concise, and accurate information on a wide range of topics. Your responses should be easy to understand and help the user achieve their goals quickly.


user
Do pilots of civil aircraft know the exact weight of the aircraft prior to take-off?


assistant
No, not the exact weight.  They estimate the likely weight, with a margin for error, and on more modern aircraft (like the A330), onboard software will calculate the actual weight once airborne and then suggest the optimal angle of attack for the flight.