The airports also lacked other security measures, such as perimeter lighting, a new study says.
Only one of 10 cargo-only airports visited during a government watchdog study had an electronic intrusion detection system even partially installed, according to a security assessment released Monday.
Only two of those airports currently screen pilots and noncommercial passengers and none screens packages and cargo, according to the report from the Government Accountability Office.
All the airports had more basic security in place, though, such as lighting by hangars and fencing around the full perimeter, and nine out of 10 are at least partially monitored by closed-circuit TV, the report said.
The GAO report was based on on-site assessments of 13 general aviation airports located within 30 miles of a metropolitan area with 1 million people or more. The airports all house airplanes of 12,500 pounds or more and have at least 5,000 takeoffs and landings each year.
Three of the 13 airports also serve commercial passenger flights and so are required to adhere to Transportation Security Administration security requirements such as screening cargo and passengers, lighting the entire airport perimeter and installing an electronic intrusion detection system.
General aviation airports that don't serve commercial passenger flights for the most part are not required to implement TSA regulations, though the agency issued a list of voluntary security recommendations for those airports in 2004.
TSA also has created an online tool for general aviation airports to assess their own security.
Senate Commerce Committee Chairman Jay Rockefeller, D-W.V., has called general aviation airports the "weak link" in the nation's defense against another 9/11-style terrorist attack. Rockefeller requested the report along with Commerce ranking member Kay Bailey Hutchison, R-Texas.
The surveyed airports reported several instances of unauthorized access to airport grounds over roughly the past decade, GAO said, including at least two that resulted in airplane thefts. Those airplanes were later recovered, the agency said.
"The damage that can be caused by even small general aviation aircraft was demonstrated by the February 2010 crash of a single-engine plane into an Internal Revenue Service . . . building in Austin, Texas," GAO noted. "Larger aircraft, such as midsize and larger business jets, could cause catastrophic damage to structures and pose a greater risk if they are located near major metropolitan areas."
House Transportation Committee Chairman John Mica, R-Fla., hadn't yet reviewed the GAO report Tuesday afternoon, a spokesman said.
Rockefeller's office did not immediately respond to a request for comment on the report.
Because noncommercial airports aren't bound by TSA regulations, GAO stressed, the report does not mean that they failed a security test. Its assessment also didn't account for security precautions the individual carriers might have in place, the agency said.
General aviation includes all flights other than regularly scheduled passenger and cargo flights and military flights, such as corporate, recreational and training flights and hospital airlifts. It accounts for about three-fourths of U.S flights, GAO said, including more than 200,000 aircraft, ranging from small propeller planes to the Boeing 747, at more than 19,000 facilities.