Question:
The tracking and tension of the blade on my bandsaw have been correctly set and adjusted but after a few cuts the blade moves to the front edge of the bandwheels, and on one occasion flew off the wheels altogether.

Answer:
If you tension the blade fully after tracking you will alter the tracking, this may be the problem. When tracking, the wheel needs to be spun quite a few revolutions by hand for the blade to settle down and find its line. The blade should be tracked to the centre of the top wheel. It also  advisable to check the thrust bearings position on the blade guides to make sure these are not forcing the blade forward and off the wheels. Blade tension should also be checked because an under-tensioned blade will move on the bandwheels when a work piece is being cut and pressure is being applied to the blade.