If an aircraft is loaded 90 pounds over maximum certificated gross weight, how much fuel should be drained to bring it within limits?

To bring an aircraft that is loaded 90 pounds over its maximum certificated gross weight back within limits, it is important to understand how much weight is represented by a gallon of aviation fuel. Typically, one gallon of avgas weighs about 6 pounds.

To determine how much fuel needs to be drained, the calculation involves dividing the excess weight by the weight per gallon of fuel. In this case, we take the excess weight of 90 pounds and divide it by the weight of one gallon of fuel (6 pounds):

90 pounds / 6 pounds per gallon = 15 gallons.

Therefore, to bring the aircraft within limits, 15 gallons of fuel must be drained. This makes this option the correct answer, as it accurately reflects the necessary action to ensure safe flying conditions by complying with weight regulations.