Do you know what the juiciest terrorist target at the airport is besides an airliner full of hundreds of passengers? Its the queue of hundreds of passengers waiting to go through the security screening. Its odd those have never been attacked by those crazy religious fanatics.
Because there could be armed security people walking around at airports. Terrorists are afraid of being shot before killing many people. From the terrorist’s point of view, the airplane is a gun free zone and easy to overpower.
Almost all mass killings occur in gun free zones.