Getting on track from having a start point as a landmark is easy enough, but directly from the airfield I can see it being quite easy to be a mile or so off track
Back in the days when we used 4 figure Lats and Longs a mile was considered to be satisfactory.
If you draw a line on a map you should be able to eyeball which side of it you are. Unless you have a bomb aimer's window, like most Russian transport aircraft, you cannot see directly below.