Why are Foreign students able to study at U.S. flight schools after entering the country illegally or without undergoing a required security check?

The Government Accountability Office (GAO) reported Wednesday that its investigators found that eight foreign nationals attending a Boston flight school in March 2010 had entered the country illegally. Seventeen more who received security checks had overstayed their allotted time in the country.

Three of them had obtained pilot's licenses, Stephen Lord of the GAO told the House Homeland Security subcommittee on transportation security.

Investigators also found that an undisclosed number of foreigners among the 25,599 registered with the Federal Aviation Administration to train to fly were not in a Transportation Security Administration (TSA) database and hadn't applied for a security check.

"We were surprised to find that some — the exact number is designated sensitive security information — some of the foreign nationals holding pilot's licenses were not in the TSA's database, indicating that some foreign nationals hadn't been vetted before receiving flight training," Lord said.

Three of the 9/11 hijackers who slammed planes into the World Trade Center, the Pentagon and a field in Pennsylvania were trained to fly at schools in Florida, Arizona and Minnesota.