My opinion, and that's all it is, because I am not a CPA, is that if you are buying an airplane to get a financial benefit, you are looking into a deep dark hole. On the other hand, if you do it the other way, i.e., buy an airplane because you love to fly and enjoy helping others (cancer patients, heart patients, diseased children, cats and dogs) then you can deduct certain expenses. The costs of fuel, oil, parking, ramp fees and perhaps other similar direct expenses of making a particular flight for Pilots'n Paws are right now most likely deductible as charitable donations. I say "most likely" because it may change and I don't want someone to quote me. Read on this site and you should find that such flights need to be documented here in these forums as to the original request and subsequent posts in response to the original request. My understanding is that other costs such as insurance, hangar rent/tie-down rent/ annual inspections, routine maintenance, etc. are not deductible for PnP purposes. Also, financial records of each flight should be kept for future reference at tax return time.
In fact, I believe if you are renting you can deduct the rental cost of the airplane including fuel, so if you are looking at the bottom line of operating an airplane for flying Pilots'n Paws flights, renting is more fiscally attractive than owning.
I own a 1969 Cessna 172. I am flying tomorrow a 500 mile round trip as part of a rescue to get an 8 year old dog from Texas to Florida. Am I doing it to reduce my taxes? No. Am I doing it because I like to fly? Partially. Am I doing it because five years ago I had heart surgery and felt a deep emotional need to "give back" to others in need? Absolutely. I enjoy flying and I feel I would be flying so many hours per year for some purpose, like eating a "$100 breakfast" so why not use my airplane to help others?
There's my opinion...for what it's worth. I hope that helps you in your decision making.
P.S. Read this page on another PnP forum: viewtopic.php?f=27&t=24024
P.P.S. And here's some more info. viewtopic.php?f=4&t=6821
There really is a lot of useful information on this site that is not hard to find if folks would just look for it. I found the above in less than five minutes.
Cessna 172/Decatur, AL - Pryor Field (DCU)