General Aviation Security: Increased Federal Oversight Is Needed, but Continued Partnership with the Private Sector Is Critical to Long-Term Success, GAO-05-144, November 10, 2004, Highlights.
“Federal intelligence agencies have reported that in the past, terrorists have considered using general aviation aircraft (all aviation other than commercial and military) for terrorist acts, and that the September 11th terrorists learned to fly at general aviation flight schools….TSA has not yet developed an implementation plan for its risk management efforts…FAA has not established written policies or procedures for reviewing and revalidating the need for flight restrictions that limit access to airspace for indefinite periods of time and could negatively affect the general aviation industry.”
