On Wed, 12 Sep 2001, Terry Collins wrote:
both planes were turning a circle into the towers (one wing higher
than other) and I would consider that much harder than follow the
straight line.
They were most likely flying the planes by hand. A perfectly straight
line can indeed be quite difficult to fly; corrections need to be made.
In the second WTC crash, for instance, you see the plane banking left at
the last minute and notice later that, while it dealt a most damaging
blow, it was a little right of center. The pilot was trying to make a
correction.