WASHINGTON, DC (CNN) -- Some foreign students who enroll and graduate from U.S. flight schools are in the U.S. illegally, despite extensive post-9/11 efforts to vet student pilots, congressional investigators said Wednesday.
Stephen Lord, an investigative chief with the Government Accountability Office, declined to say how many student pilots he found to be wrongly in the country, saying that the Transportation Security Administration had deemed the number to be "sensitive security information."
But, he said, his study showed "weaknesses" in the TSA's vetting process that need to be fixed.
MORE: Complete GAO Report
The holes are "extremely disturbing," House Homeland Security subcommittee Chairman Rep. Mike Rogers said.
"It's completely unacceptable that a decade after 9/11 GAO has uncovered weaknesses in our security controls that were supposed to be fixed a decade ago," Rogers said.
Several of the terrorists who carried out the attacks of September 11, 2001, including leader Mohammed Atta, trained at U.S. flight schools before conducting their attack, and government leaders vowed to prevent such a mistake from happening again.
Today, the TSA vets foreign student pilots against terror watch lists and conducts fingerprint-based criminal background checks, but it does not vet them against immigration databases, the GAO lead investigator said.
Lord said his group downloaded an FAA database of pilots and compared it to TSA's database of student pilots who had completed background checks.
"In a perfect world, the two databases would match," Lord said. "But we were surprised to find that some ... of the foreign nationals holding pilots licenses were not in the TSA's databases, indicating that some foreign nationals had not been vetted before receiving flight training, and ultimately receiving pilots' licenses."
The hole first came to public light in 2010 when local police stopped the owner of a Massachusetts flight school for a traffic violation and discovered he was in the country illegally. Federal immigration officials investigated and found that 25 of the foreign nationals at the school had been vetted by the TSA and had been approved to begin flight training. But further investigation revealed that eight of the students had entered the country illegally and 17 had overstayed their visas.
Kerwin Wilson, the TSA's general manager for general aviation, said the TSA is taking steps to address the matter.
"We do have a plan in place. We're working very closely with ICE (Immigration and Customs Enforcement) in terms of automating the process to ensure that TSA is also checking for immigration status as well as the Terrorist Screening database," he said.
Rep. Chip Cravaak, R-Minnesota, said the government needs a "common-sense solution" to prevent another 9/11-style attack, but said no solution would be perfect.
"We will never have 100 percent security. That just won't happen. Somebody that is perfectly normal one day can flip, because of whatever pressures he or she is under," he said.