Relying on legal adivce here probably is not the best idea. You need to consult an attorney.
In addition to asking whether:
you will also be asked:
You need to start by reviewing your employment agreement/contract and state law for both where you work and where the company is headquartered. And then check with a lawyer.
IANAL, but my first guess would be that ABC company owns the copyright. While it may not be in your job description to write software, you wrote it while employed by them and it appears that you are using it as part of your job for them. In effect, you took it upon yourself to make your job easier (and the job of your company) while in their employ. It all goes back to them.
If the airport is using it not in context of the work your company does, it could be even stickier. Your connection to the airport is because of your company, so that could create implied consent that you may have overstepped.
This could be a sticky issue, state and federal law is not always clear or in agreement. If you have real concerns about trying to maintain ownership, you need to talk to your management and a lawyer.