When you purchase a plane, you typically put in all at once, when you request an aircraft, the order is usually taken up by someone known as a broker (can be official or unofficial) and sell the plane to you at the markup you choose, and you only have to give half of it to the person upfront, and the other half afterwards, though beware, if you don't accept the plane after a certain amount of time (usually 72 hours, I think that is the minimum I think), the broker can go with your aircraft and the cash you paid for it and do what he wants with it.
