Can I rebook on another airline if my flight is cancelled?

Maybe — but the airline isn't required to do it. Under DOT rules, when your flight is cancelled, the airline must offer either a full cash refund or rebooking on one of their own flights. They are not required to book you on a competitor's flight.

That said, many airlines have interline agreements that allow rebooking on partner airlines during irregular operations ("IRROPS"). Whether you get this depends on the airline, the situation, and often how you ask. Gate agents have more authority to make this happen than phone reps, especially at hub airports where multiple carriers fly the same route.

Tips that actually work: Ask the gate agent (politely but firmly) if they can "endorse your ticket" to another carrier. Use the phrase "interline reprotection." If the agent says no, ask for a supervisor. Airlines are more willing to do this on busy routes where they know they can't get you out for hours.

If the airline refuses to rebook you elsewhere and their next available flight isn't for 24+ hours, take the full cash refund instead and book yourself on another carrier. The refund must be issued within 7 business days for credit card purchases. Sometimes this is faster and cheaper than waiting.