U.S. Failing to Track Schools Granting Visas, Report Says WASHINGTON - More than one-third of the flight schools in the United States that cater to foreigners are not certified by the Federal Aviation Administration, according to the Government Accountability Office, raising concerns that the schools are illegally backing student visas although they have no intention of teaching the students to fly. The Immigration and Customs Enforcement agency, which oversees the student visa program, keeps such sloppy records that it does not know how many of the 10,000 schools that can submit paperwork for such visas are accredited by the states where they do business, according to a new G.A.O. report. It said 167 of the 434 flight schools in the United States were not accredited by the F.A.A. and could not provide students with the proper documents to show they know how to operate a plane. The report, which is scheduled to be released on Tuesday, said that even if schools are already under investigation for issuing documents for illegal visas, the customs agency does not have the authority to stop them from issuing more. Three senators - Charles E. Schumer, Democrat of New York; Charles E. Grassley, Republican of Iowa; and Dianne Feinstein, Democrat of California - asked the G.A.O. in 2011 to investigate how the customs agency, which is part of the Department of Homeland Security, issues student visas. The senators requested the inquiry after it was revealed that Tri-Valley University of Pleasanton, Calif., had provided foreigners with paperwork for student visas, with no intention of educating them. After the school was shuttered, roughly 1,000 students, many from India, had their visas taken away and were forced to wear ankle bracelets until their status was resolved. "The report shows that more than a decade after the 9/11 attacks, the student visa program remains dangerously vulnerable to terrorists," Mr. Schumer said in a statement. These sham schools are providing a dangerous, back-door entrance to the United States. The California scheme, he said, "was just the tip of the iceberg." Two of the hijackers involved in the attacks of Sept. 11, 2001, received federal approval for visas - in March 2002 - to attend a flight school in Florida. Gillian Christensen, a spokeswoman for ICE, said in an e-mail that the agency has "already begun addressing the G.A.O. recommendations." Mr. Schumer plans to include many of the report's recommendaitons in a bill, to be introduced Tuesday, that would require all schools to show proof of state licensing and would increase penalties for illegally backing visas.