The borescope inspection on the 131-9B APU is not scheduled in a maintenance task. Still it can be necessary to carry out a borescope inspection. It has occurred that the compressor and turbine were rotated by turning the turbine through the exhaust hole using a wooden stick. This can cause damage to the turbine (one of the most expensive components of the APU), a reason why this is ABSOLUTELY NOT PERMITTED. The correct way to turning the APU compressor and turbine is stated in AMM task 49-21-00-980 801, and is done by using a wrench which is inserted in the gearbox.