I assure you the pilots are very aware of the fuel situation well before they begin to taxi. Sometimes it is easier to just burn to excess fuel off versus de-fueling at the gate.

It would be beyond shocking if the flight crew didn't know what they had onboard for fuel, what they needed and what they can safely land with. Do you really have facts for this?

That's part of the whole kabuki dance just before the push when you see the GA and a tarmac worker present the Captain with a pax count, a bag count and a fuel slip.

It's entirely possible that the aircraft was just a little overweight and that holding a bit or perhaps burning a bit more enroute is more efficient than off-loading.

OK, the incident of which I'm thinking happened last year, soon after 3-3. My memory at this point is definitely fuzzy, so I would make a terrible witness for the either the prosecution or the defense. I had the impression, though, that we were getting off the gate quickly (I think we were at LGA) and I sort of had the idea that we were taxiing as we were waiting for the final numbers. However, since the reaction to my memory is so strong, I'm guessing its my memory that's faulty, not the pilot's procedure.

You got off the gate quickly because they had planned to sit out there burning fuel for a while. There are few time this happened to me and every time, the captain always informed us of what we had to do.

The problem is not just any empty tanker, but that the offloaded fuel is generally limited to going back onto another airplane from the same carrier, as no one else will accept it after it was offloaded from another airplane. Some locations can transfer the offloaded fuel back to the fuel farm so it can be retested and certified as fresh fuel. But if you offload 10,000 pounds of fuel from a UA airplane that tanker is out of commission until it can be loaded back onto another UA airplane, and depending on the status of the other flights that might be quite some time.

I ran into this a couple of years ago in SEA. Our 772 had a faulty APU but had already been fueled (and boarded) for SEA-NRT. UA made the decision to change the route to SEA-SFO-NRT, swapping out the plane in SFO. Unfortunately, we had way too much fuel onboard for that, and couldn't find a UA tanker to unload us.

I believe ultimately for us they flew a replacement 772 up to SEA from SFO early the next morning, as they couldn't get the fuel issue resolved before the crew went illegal.

This is very important in the equation. After removing fuel from an aircraft, the fuel is considered contaminated and it would be on the airline to find a destination for it. The vehicle into which the contaminated fuel goes is now considered contaminated. I would suggest it would never be return to the fuel farm, as the process to clear the fuel would be extensive.

Another issue is the fueler itself. Contaminated fuel is typically put into a defueler only. It’s the same vehicle, but it is specifically designated to handle defuel operations. One cannot easily turn a defueler into a fueler – it requires a certification process and additional costs and time.

That said, it is often much more efficient and quick to burn excess fuel rather than locate and undergo defueling operations. The quantity of fuel to be burned was obviously so large that the time and expense for defueling was economic.

A lot of times, whatever isn't used to fuel that carrier's planes, is transferred to another truck where it's used to fuel various diesel equipment around the airfield.

Must be those new highly efficient bio-diesel engines.

The two aren't hugely different, although different additives. Blending some jet fuel with auto-diesel can be done and the trucks still go.

At their very heart, they are both straight kerosene. Although both use different blends of additives for different operational reasons (such as lubricats for Diesel, and biocides for Jet-A,) Diesel engines will burn jet fuel, and jets will burn Diesel just fine otherwise. The main difference between the two engines, really, is that Diesel is high compression, and turbines are low compression.

Random useless knowledge: refineries that make jet fuel have to make it for a certain number of months before it can be certified for use in airplanes. Until it is, it's usually sold as plain ol' heating kerosene at the local gas station.

How do you figure?
Typical diesel engines are about 15:1 CR which is a pressure ratio of 44:1.
Typical airliner turbine engine operating pressure ratio is 30-50:1.

I'm not sure where you got your numbers there. High-bypass turbines run about 16:1 compression. Regardless, the overall air pressure ratio has dropped from that number once it reaches the combustion chambers.

I understand that at least one key reason for this is that the aircraft's wings are not designed to withstand substantial flex in a downward direction, which is what would happen at touchdown if they were weighed down by large amounts of fuel.

http://en.wikipedia.org/wiki/GE90#Sp...28GE90-115B.29 says "Overall pressure ratio: 42:1"
It's about 2:1 on the LP spool and 23:1 on the HP spool. There's very little drop from P3 (CDP) to the combustor.