What does not affect the total allowable weight when performing a weight and balance check?

When performing a weight and balance check, personal items in the cockpit do not affect the total allowable weight of the aircraft. The total allowable weight is primarily concerned with the aircraft's structural limitations, which include the empty weight, installed equipment such as seats, and operational weight such as fuel.

The empty weight of the aircraft is a critical component in calculating the weight and balance because it represents the basic weight of the aircraft without payload or usable fuel. The weight of installed seats is also significant, as it directly contributes to the overall weight that will impact performance and structural integrity. Fuel levels play a crucial role, too, since they add to the weight and can vary significantly based on how much fuel is loaded in the tanks.

Personal items, while they can add weight, are not factored into the standard calculations for the weight and balance limits as they are typically considered variable and not a fixed part of the aircraft's operational weight. Therefore, they do not have a direct influence on the allowable total weight for performance calculations, making this choice the correct answer.