When we learn to fly, one of the first lessons is how to taxi. In the general aviation world, there isn’t a great deal of difference when it comes to taxiing one airplane versus another. The differences are relatively minor, and getting the airplane in and out of a tiedown spot is just a matter of practice.
As you move up the chain, though, taxiing larger, longer aircraft is different. Pilots may go years, or even decades, without actually taxiing an airplane, and the move to the left seat can be a bit of a challenge. The sight picture is different, and you steer with your hand using a tiller, not with your feet using rudder pedals. Longer airplanes, like the Boeing 737-900 and up, require more planning for a turn in order to avoid hitting taxi lights and other objects.
It's in the gate areas that things can get especially dicey. The days of just turning to meet a taxi line are over. In fact, if you ever look out the terminal window at a ramp, you’ll often see a multitude of lines. Some gates can only be used by certain airplanes, and others have separate lines for airplanes of a different size. Often on the ramp you will see red lines (or some other code of color) that generally correlate to the outline of an airplane. These are safety boundaries, and they serve a couple of purposes. The airport and airlines have done the math to determine that all ground equipment needs to be kept out of these lines. Bag carts, belt loaders, fuel trucks, and other vehicles must all be outside of the safety area unless they are specifically serving an airplane.
Another purpose, sort of tied into the above, is for deicing operations at the gate. If the airplane is properly parked, and other equipment is out of the way, a deicing truck should be able to properly deice an airplane using the safety area as a guide, without fear of hitting either the airplane or the other equipment or vehicles.
It is also important to learn to allow room enough to turn so that the extended centerline of the fuselage is aligned with taxi line. The airplane must be as close to parallel as possible. If it is at all off-center, it can have huge ramifications. Remember, the wingspan is over 100 feet, so even a slight cattywampus of the airplane could leave the wing or the tail exposed for unexpected contact with another airplane or vehicle. Believe it or not, it happens.
Taxiing is one of those things that looks easier than it is, and that’s especially true of larger airliner-type aircraft. When it’s your time to take the left seat, take your time to really master the sight picture and go slow. Don’t just follow the lines—be the lines!