For the set they built an entire Airbus A330 to 1:1 scale including a functioning cockpit.
While since 9/11 cockpit doors and locks have been strengthened, it is a misconception that pilots cannot open cockpit door during flight. They can and do. Pilots and flight deck crew are allowed to step outside to use the restroom, let flight attendants bring in food, or switch crews for rest purposes and do so on almost all flights. Less commonly they also open door to look for any malfunction on wing control surfaces or avionics or flight control access points that are not all in cockpit.
The aircraft's registration is G-KNDM.