I did do a search for this question and didn't find any answers in the forums. I checked the FAA website and according to FAA, passengers may be charged up to $4.50 for each 'enplanement' in domestic airports. The regulation gives examples and in each case only shows 'boarding' of plane; not departure or 'landings'.

1-3. AUTHORIZING LEGISLATION. The PFC is authorized by 49 United States Code
(U.S.C.) §40117, which is referred to as the “Statute.” The PFC statute’s broad
objective is to provide funds through the local imposition of a $1, $2, $3, $4, or $4.50
charge per enplaned passenger. (emphasis added).

Also, these charges are not permitted to be applied when frequent flier miles are used for ticketing; only paid tickets pay these fees.

Here's my scenario: depart: MIA>LIM; return: GIG (Rio De Janeiro)>ATL; change planes, ATL>MIA.

I think my PFC should be $9; I've been charged $16...my logic: enplane at MIA; deplane at ATL, then enplane again at ATL...max $4.50 each enplanement = $9.00

Any error in this logic; any suggestions? These flights were booked thru an 3rd party...maybe an error in their invoicing??

Thanks.