[rudderboost]

In a jet (well the larger and more modern jets) you rarely "top off" the tanks on shorter trips. In a larger jet you can carry large amounts of fuel, and if you are going shorter distances it just doesn't make sense to carry all the extra weight. If you were flying 400 miles in a Lear 60, it would take less than an hour, but if you topped the tanks off you would be carrying an extra 5,500 pounds of fuel. This means you would be using more fuel, just to carry the weight of the extra fuel. Not very efficient. As bigchillcar and some others are pointing out, for a good portion of a long flight (sometimes over half) you technically do not have enough fuel to make it to your destination. Then as you burn fuel off, you get lighter and it takes less power for the same speed and you "make fuel". Our "box" says we'll run out of gas about halfway to our destination, then we usually end up landing at our destination with an extra 1 hr or more of fuel. At altitude winds and temperature plays an extremely important role. 1 or 2 degrees of change is noticeable in performance at altitude. At lower altitudes we burn about 4000 pounds an our or more. At altitude it's more like 1200. I've never flown a 20 series like bigchillcar, but I've heard they burned as much fuel idling on the ground than they did at cruise! Maybe bigchillcar can set us straight on that.