Shortly after the events of 11 September 2001, U.S. Department of Transportation chartered an industry team to make recommendations to improve aircraft security. One of those recommendations was to change cockpit doors in order to deny access from intruders. Modifications have been completed on the door of all U.S. airliners and the doors on international carriers that serve the U.S.

Other Resources
Airlines with No Fatal Events
Suggestions for Increasing Hijack Threats
Fatal Events by Airline
Accidents and Incidents by Airline
Dealing with In-Flight Biological and Chemical Threats
Chemical and Biological Warfare Agents