APU hours verus Airframe hours is going to be different for a B747 utilized by AirNZ to one used domestically by JAL for example. Where the aircraft is used on predominately long haul the APU hours v Airframe hours will be very low. In the JAL case where the B747 can be a domestic "air taxi", it may be almost equal. It is like asking how long is a piece of string, unless you specify in what type of operation the aircraft is used.