Originally Posted by flygirl555
I was curious...Do airlines fuel aircraft based on their expected load capacity or do they always fill the tank each time they land? For example, if an aircraft can hold 200 passengers, but they know only 100 people to be on board for the flight, do they still top-off the tank or do they only fill it 3/4 of the way up?
I'm sure there are some references on the web available just by doing a Google search but how much fuel is used depends on a lot of factors.
There are FAA regulations/guidelines for determining the weight of the aircraft based on the number of passengers indicated. So, that generally goes into fuel calculations along with: the weather, wind direction and speed, cruising altitude (based also on weather, traffic and other factors), how far away the destination airport is and then some. They also keep enough fuel to turn around and go back, or, fly to an alternate airport (an alternate airport near the originally intended destination airport is generally figured out ahead of time for fuel calculations). There is also a "holding pattern" reserve calculated in the fuel, and a 30 minute backup reserve on top of that.
Gasoline, by the way is not used, but Jet A (or other types of jet fuel) are used. Jet engines require absolutely pure fuel and jet fuel is far more pure than the gas you pump into your car. An interesting fact about jet fuel is that it is similar enough to diesel that jet fuel can be used in H1 hummers. :-)
Hopefully this has somewhat helped answer your question.