I'm finding this one hard to swallow.
You're employed as an aviator, as part of a collective bargaining agreement, and worked for a year without knowing that your work is covered by a CBA?
Are you saying that the employees of a particular company are all covered under the CBA?
Generally a CBA covers a particular subset of the employment of a company; pipefitters, or pilots, or flight attendants, or welders. If a company has pilots and flight attendants and mechanics, generally they are all responsible for voting themselves into a collective bargaining situation. There's a lot to unpack in your statement, but there's a lot of incongruity. A lot of missing information, too.
Did none of the pilots know of this representation? Were any of the pilots responsible for voting on representation, or agreeing to it? If any other pilots knew about this, did they withhold it from you?
If you're not paying dues, and if nothing is being withheld from your pay, your relationship with the union seems a bit murky. Under what grounds was the contract negotiated, and by whom? What kind of operation?
You are limited to a five-percent bonus, but you are being taxed on a bonus that you do not receive? Your comment infers that other employees receive a 10% bonus of some kind, and that you receive half that amount, but are taxed on the full amount. Is this the case?
It doesn't sound like you have representation, or that any terms have been negotiated for you. Before considering whether you can "opt out," a determination needs to be made regarding what you are "in," first. There's a lot of information missing here. Given your situation, a public discussion may not be appropriate.