Final answer:
The correct flap setting for takeoff is influenced by multiple variables and is typically found in the aircraft's operating handbook or airline procedures, with common settings ranging from 5 to 15 degrees for commercial jets.
Step-by-step explanation:
The flap setting for a departure from RWY 31L at the planned takeoff weight is dependent on several factors including aircraft type, weight, runway length, altitude, temperature, and wind conditions. Typically, this information can be found in the aircraft's operating handbook or the airline's standard operating procedures.
For most commercial jets, common flap settings for takeoff range from 5 to 15 degrees, but the exact setting is calculated for each flight based on the previously mentioned factors. This calculation can be done manually or by using takeoff performance software which provides pilots with the necessary data to set flaps appropriately for a safe and efficient takeoff.