Soon as I saw that tractor with the apu in it, some crazy memories came back. I used to be a mechanic at an airline that had a couple of Boeing apu's mounted in the back of Ford pickups. They were used as air starts, both on the 747s and one on the 2 and 3 engine aircraft. Inspections and maintenance were done regularly by us mechanics, and it was fun to do a run up for a nozzle pressure test. If the cycle wasn't done right, it would not light up, and excess fuel would be sitting in the turbine. When it did finally fire up, the canopy covering the engine would almost lift off the back of the truck. Back in those days I did a lot of afternoon shifts, means working in the dark. The rampies would have both hooked up to a 747 and do a couple of false starts on one or both. Get a call on the radio, hussle up to the ramp and see what's going on. Then the shit hits the fan. Time is everything with aircraft departure off the gate. Pull the airstarts off the plane and well away, everyone stand back, and then go through the cycle and hope like hell it lights up. Sometimes it didn't. But if it did, very impressive, and scary, heart pounding moments. Some of us have seen wet starts on jet engines, kind of neat to see when you are not on the aircraft. The little Ford 150 would be almost engulfed in a fire ball as the Boeing turbine fired. After a few minutes it would get moved back under the 747, nozzles connected and hope they have enough pressure to turn its engines. If it did, all was good and time to go home. If not, then I am on the hook for a delay, and got some splainin to do.