As a private pilot under Part 61 E (61.113), it states that: (https://www.ecfr.gov/cgi-bin/text-idx?SID=3f5641add742ba4c45790a373c19267b&mc=true&node=se14.2.61_1113&rgn=div8)
"A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:
The flight is only incidental to that business or employment; and
The aircraft does not carry passengers or property for compensation or hire.
A private pilot may not pay less than the pro rata share of the operating expenses of a flight with passengers, provided the expenses involve only fuel, oil, airport expenditures, or rental fees."
Rental fees generally must include more than just fuel, oil and airport expenditures (however that is defined). Obviously, rental costs would need to cover aircraft maintenance, fuel, oil, insurance, hangar, etc... or the rental business would operate at a loss.
If the aircraft is owned by the pilot (not rented), is the owner able to calculate a rental cost based on an annualized cost over projected annual hours similar to an aircraft rental business? Or as a private owner, are we limited to only fuel, oil and airport expenditures (again,...whatever that is)?
-W