Less than a year after the December 21, 1988, bombing of Pan Am Flight 103 over Lockerbie, Scotland, the President's Commission on Aviation Security and Terrorism recommended improvements in FAA security bulletins, leading to the creation of Security Directives and Information Circulars. In 1990, section 9121 of the Aviation Safety and Capacity Expansion Act of 1990 (Pub. L. 101-508) broadened 14 CFR Part 191 to prohibit disclosure of "any information obtained in the conduct of security or research and development activities." The Aviation Security Improvement Act of 1990 (Pub. L. No. 101-604) required minimizing the number of people with access to information about threats, often contained in security directives (SDs) and information circulars (ICs). On March 21, 1997, FAA revised 14 CFR Part 191, and changed its title to "Protection of Sensitive Security Information." It also strengthened the existing rule to protect SSI from unauthorized disclosure, expanded its application to air carriers, airport operators, indirect air carriers, foreign air carriers, and individuals, and specified in more detail the information protected to include SDs, ICs, and inspection, incident, and enforcement-related SSI.