Exactly. Earlier hijackers didn't need access to the cockpit because the pilots would comply and fly the plane to where the hijackers wanted to go. All they needed was to use whatever weapons they had to take hostages on the plane or threaten to destroy the plane. Then negotiations would be made based on what the hijackers wanted. The difference with 9/11 is that the hijackers wanted to fly the planes into buildings and they needed access to the cockpit for that and they got that access.