Hi Jutes85, Buzz here. When i was in the Air Force (in the '80's) a few mechanics were engine run qualified. But it took a pilot to taxi.
At UAL they get a few people on the crew qualified to static -run, or taxi, or high power. It depends on the needs of the crew - you are "invited" by your Lead Mechanic, or Foreman to shoulder the responsibility of possibly causing lots of aircraft damage. OK
, so i've got more of-road time in a 737 than anybody else i know (grin)
After you become a Line Mechanic and are assigned to a crew, you get to go to a week of Systems Introduction. It's a basic class of what's related to what on an airliner. Next you work on the airplanes for "a while".
If your Lead thinks you can handle the stress, and has need of another pit mechanic, you go to the first phase of the taxi-run classes. We would spend a week learning the pit, and what the different systems do, and take a few tests.
In the previous century we'd get to go to DEN
and have disaster drills, make mistakes electronically in the flight sims. This was generally late at night between 10 pm and 2 am (no problem for us midnght guys). Yes, we'd take turns flying the sims.
Next you go back to your crew and hook up with hour freindly neighborhhood DST (designated station trainer) who would walk you through engine starts, simple system tests.
After you're comfortable with that, you get to learn to taxi. I find most people drive well, but talking to "the guys in the glass house" (the tower) is difficult. And they get used to working as a crew in the pit - one guy shouldn't do it all. 2 brains, 2 sets of eyes, 2 ways to prevent a screw-up.
Then you get to make the DST nervous - high power tests. After a fuel control change, or a few other things we have to take the airplane out to the Hush House and go to takeoff power. Mechanics get to do this, very few Line Pilots are willing to wait up all night to see if what we worked on is OK
And we test the engine work differently than a Line pilot does. I don't know of pilots who will sit still and lock the brakes, and ram one throttle full forward, while the guy in the other seat has his head down timing the acceleration.
Besides, it's kind of satisfying to test your work. I've done DC-8's, Dc-10, 727, 2 kinds of 737, 757,and A320.
Buzz Fuselsausage: Line Mechanic by night, DC-3 Crew Chief by choice, taildragger pilot for fun