"Short answer is the contract the cadet signed."

Involuntary servitude went out with the 13th Amendment.  Short answer is that he can't be required to work for them, or for anyone.  The contract can require that he pay the money back if he qualifies for the job but doesn't accept it. 

I don't know that airline legal departments get involved in what 1099 to file.  If this is American Airlines, which offers $7,500 signing bonus to "senior cadets" through its PSA subsidiary, they have their hands full with real issues.   " A December 2025 federal lawsuit filed in San Diego alleges American Airlines (AACA) and partners discriminated against 18 minority cadets (Black, Asian, Latino), claiming "reverse redlining" and unfair, excessive remedial training that forced them to quit, despite initially targeting them for enrollment. The suit alleges fraud and creating a hostile environment."