Ten years after the Sept. 11 attacks, stricter federal screening makes it harder for possible terrorists to enroll in U.S. civilian flight schools. But the system still has loopholes. The TSA only checks fingerprints, criminal backgrounds and terrorist watch list names for foreign students — not for U.S. citizens. And inspectors are supposed to visit FAA-certified flight schools once yearly to ensure students have proper identity documentation and visas. But numerous freelance flight instructors only get irregular inspections.