Originally Posted by
sdsearch
Well, not all airplanes run with full fuel. It adds extra weight.
At any rate, for whatever reason(s), the amount of fuel loaded can differ greatly on a 7-hour flight on one airline on one route vs a 3.5-hour flight on another airline on another route.
Furthermore, the policies on that may differ by airilne and/or route and/or maybe even crew (on or off ground). There was a recent episode of On The Fly where they first think they have to kick off 4 passengers due to excess weight, then only 1, then play some magic and don't have to kick off any. (After the pilot says he can only adjust fuel by passengers, cargo, or fuel.)
If the short runway of MDW leads to underloading of fuel, then that would only affect airlines that serve MDW. Most if not all legacies serve ORD instead. ORD doesn't have short runway. (It may or may not have enough for all weather scenarios, but that's a different issue than whether they're short.) So by flying an airline that uses ORD instead of MDW, you may be able to avoid whatever short runway issues there are and their effect on fuel loading.
In reality, very few airlines operate with fuel tanks, since fuel loads are by nature and necessity mission-specific, and a delicate balance of several factors (as far as weights go) such as max takeoff weight, max landing weight, planned flight duration, weather/winds, and the planned payload (pax, bags, cargo) to be transported.
If a flight is takeoff-limited and the temperature at actual departure time is lower than originally planned, recalculating the max takeoff weight to the lower temperature usually results in a higher weight, and enabling the flight to now take everyone and not leave anyone behind. Conversely, if the temperature spikes up a couple of degrees warmer than planned, then the max takeoff weight decreases, and that may entail returning to the gate to offload weight in excess of what's permissible for that new hotter temp.
This used to be a real PITA for airlines operating from the old DEN Stapleton (and other "hot and high" airports) with the previous generation of airliners powered by Pratt & Whitney's venerable JT8D engine (which were on the 727s, DC-9s, and 737-200s of the era) but it is much a problem with the high-bypass engines common on most of today's operating aircraft (the exception being the MD-80, which still uses a later version of the JT8D). That said, MDW or DEN at 100F+ gets rather interesting and we stay busy.
Most airline flights are not actually takeoff weight limited, but are landing weight limited, i.e. they could get the aircraft off the ground at max takeoff weight at the departure airport, but then after consumption of the fuel it takes to get from A to B, they'd be arriving over max landing weight. The solution is to add the fuel to be consumed A to B to the max landing weight at B, and then restrict the aircraft to that figure so that the flight arrives not to exceed max landing weight. On a landing weight limited flight, the temperature at the takeoff airport will then usually have no effect as far as being able to get more passengers aboard the flight.
As far as the "underloading" of fuel is concerned, there are specific requirements in the FAA regs that cover fuel planning, and the minimum fuel load is what the dispatcher and captain must concur upon as to what's safe and legal to operate the flight. If that minimum fuel requirement won't permit all the passengers to go, other options (including fuel stops) are considered.