After 9/11, there was a push to immediately do something, anything, that would prevent a repeat of the hijacker’s actions. One of the very first things that was done was the grounding of all general aviation airplanes. Then, you could fly GA but only with a filed flight plan. A curious reaction, since the Twin Towers were not hit by a GA plane, but a fully loaded airliner that had the requisite punch to make a difference (unlike general aviation planes that have hit buildings both before and since 9/11 with minimal impact), and all the hijacked planes had filed flight plans. Finally, the newly created TSA implemented new rules that prohibited non-US citizens from flight training without a background investigation.
Does this make a difference in airline security? Doesn’t matter- it’s required now and whatever your opinion of its relevancy or usefulness, compliance is not voluntary. So what does this mean to you?
Before your first lesson in either the sim or the airplane, you must be endorsed by your instructor. By law, every CFI must see either a birth certificate (raised seal) and government-issued photo ID or an unexpired U.S. passport. There are other documents that can be used but these are the two most common methods of showing U.S. citizenship.
Once your CFI is satisfied, he must either keep a copy of those documents for five years or make an endorsement in both his, and the student’s logbook. I prefer the endorsement method myself as I don’t want to be responsible for a hard-copy of someone’s documents.
The burden is completely on the CFI or flight school to satisfy these requirements- the flight student is responsible for providing authentic documents. But don’t take this lightly- the TSA regularly audits our instructors and there are criminal penalties for not-compliance.
You can find a more comprehensive account from AOPA here.