Light emitted from a semiconductor laser is converted by a collimator lens into a collimated light, which enters into an objective lens of high NA and forms a condensed spot within an optical disk. The system includes a gas turbine engine as a first motive power source, and one or more battery packs as a second motive power source. Each bore has a diameter sufficient to receive the shaft of the golf tee when the shaft is inserted therein and a depth that is different from depths of other of the bores. A present value for the operating parameter is determined based on the present operating point, and accumulation of dirt is determined on the air filter based on the initial and present values of the operating parameter.