Which requirement must a non-US citizen fulfill to begin flight training in the United States?

To begin flight training in the United States, a non-U.S. citizen must be cleared by the Secretary of Homeland Security. This requirement is rooted in national security concerns and is part of the regulatory framework established by the TSA (Transportation Security Administration). Non-citizen applicants for flight training must undergo a security threat assessment to ensure they do not pose a risk to aviation security. This process is mandatory and must be completed before training commences.

The other options may involve additional steps or documentation related to visa requirements or medical certificates, but the specific clearance by the Secretary of Homeland Security is a fundamental requirement that directly impacts a non-U.S. citizen's ability to start their flight training in the United States. Without this clearance, the individual cannot legally proceed with their training.