Anvilman, some friendly advice. Consider your position very carefully. You say you are doing volunteer charter flying, but you're not formally employed by the operator. What happens if there's an accident, particularly if a fare paying passenger is involved. Whether you're at fault or not, what do you think your liability might be? Anyone who suffers a loss at your hands will in all likelihood come after you, or your deceased estate. You're exposing yourself to lawyers who can easily take you to the cleaners for everything you have.
In answer to your question about writing off your flying training expenses against income derived from another field, you can't, simple as that. There must be a connexion between the assessible income and any allowable deductions. This is very straight forward and well established tax law. Read all about it in Tax Pack or at the ATO website should you need any clarification.