# Where is the term *pro rata* defined as it is used in 61.113(c)?

You've just received your private pilot certificate and your friends want to share the operating expenses of a flight with you. There's a mother, a father, and their 6-month old baby. Do you split the cost of the flight among three people or four?

Obviously, the answer depends on the definition of pro rata, but I can't find the definition of that term anywhere in the FARs. This term is used here:

(c) 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.

Where is the term pro rata defined as it is used in 61.113(c)?

• Generally, if a term doesn't have a definition in the regulation, the ordinary or dictionary meaning of the term is used. So I would imagine in this context, a private pilot flying $n$ passengers cannot pay less than $1/n$ of the operating costs. – Hugh Jun 13 '14 at 2:07
• Part of me thinks I know the answer, another part of me wants to forward the question to the FAA's lawyers to make sure I'm not talking out my tailcone... – voretaq7 Jun 13 '14 at 2:59
• There are legal dictionaries if you want to look it up there (Black's Law comes to mind.) But honestly, if you'd like an interpretation of a legal statute, you really need to contact a lawyer. – Jay Carr Jun 13 '14 at 4:11
• @SteveV. while the regs state that the pilot may not pay less than 1/n of the operating costs, they do not state that any other passenger has a minimum they must pay. Thus in your example, while it makes no sense for an infant to pay anything, the regs don't seem to preclude the pilot from paying 1/4 and the remaining 3/4 coming from the other passengers in whatever ratios they wish, such as the father paying 3/4 and the mother and infant paying nothing. – mah Jun 13 '14 at 10:42
• Don't you really want to be asking "What is the definition of 'passenger'?" i.e. is a 6-month-old on the flight a passenger? If so, N=4 and the pro-rata is 1/4. You don't think pro-rata is based on weight or ages, do you? – mgkrebbs Jun 14 '14 at 5:05

pro rata in law generally means according to a calculation or apportionment formula - in the context of the FARs that formula is generally assumed to be $\left(\frac{1}{nOccupants}\right)$ as Hugh noted.
The FARs specify that the pilot may not pay less than their pro rata share of operating expenses associated with the flight. So, if we have 4 occupants of the aircraft (Mom, Dad, Baby, and Pilot) and they go for a hundred-dollar hamburger the simple division method says pilot cannot pay less than one-fourth of the operating expenses associated with the flight. If we say the expenses work out to be \$100 (for the sake of easy math) the pilot has to pay at least \$25.
The FAA doesn't much care where the rest of the money comes from because it's implicit in the regulations that the pilot isn't keeping it (the money would be going into the hands of the FBO for fuel, oil, ramp fees, etc.) -- Mom & Dad could pay $37.50 each (covering themselves plus the baby) or split it up between themselves in any other way they wish and this is still acceptable under the regulations as long as the pilot has paid their pro rata share of the expenses. The pilot can certainly pay more than the simple-divison pro rata share of expenses (and generally that's the most equitable option - figure out who's paying, divide by that number, and make sure the pilot is in the "paying" group to stay on the right side of the regulations). In your example you would split the cost up among the three adults (each paying$33.33, and the pilot generally kicking in the extra penny).