There is no commercial plane service to the Northern Peloponnese (the small airport at Patras handles private aviation and limited charters). The closest airports are in Athens and in Kalamata (in the Southern Peloponnese).
Olympic Airlines offers daily one-hour flights from Athens to Kalamata's airport, 10 1/2 km (6 1/2 mi) outside town near Messinia.
Olympic Airlines (210/926-7555 Athens reservations line.)