It protects air carriers from out of control State requiremens!  

etc, etc.

Interstate air commerce is regulated by Congress.   Since it is interstate, they can't have one State enacting laws and regulations effecting federally certified air carriers differently, because it creates an unfair competition and burdens the consumer in the end for price.

Congress gave air carriers the right to compete equally, not to have a State artificially jack up prices and effect services, or to tax (directly or indirectly) the air traveler (customer).  

49 USC 41713 clearly forbid States from effecting the price, route, or service provided by a federally certified air carrier.   A State dictating to an air carrier how it must pay it's pilots is effecting both price and service directly and indirectly.   This is strictly preempted!

49 USC 42112 clearly provide for the air carrier (not the State) to deal with its labor relations.   It is the duty of the air carrier, not the State, to provide compensations, workrules, and hours.   A State dictating to an air carrier requirements has usurped the authority of the air carrier (and Congress).   It also requires air carriers to comply with the Railway Labor Act for dealing with labor, and does not prescribe any State to act as a labor representative for any party.   IOWs, air carriers and pilots/copilots are exempt from any State laws dictating labor requiremens, since it all falls under the RLA.  And that protects the public because it creates a bargaining process, managed by the NMB, where interruptions in service are not created.   State required overtime (aka, >40 hrs) are not in the State's privvy to regulate!   Nor, is the maximum workhours, or how the air carrier pays its pilots.   That's why airlines pay its pilot for fligth hours, not actual hours, and have negotiated maximum scheduled hours, daily rigs, duty rigs, vacation schedules, overnight workrules, etc.   It would (does) hamper interstate air commerce if each State dictates its own rules all across this country (and beyond)

The FAA gives air carrier certificates to air carriers, not States, and burdens (requires) the air carrier to follow particular federal labor requirements to protect the travelling public, protect the labor force, and protect the air carrier itself.   The FAA does not certify States to act in that capacity or to intercede on the Fed's authority!