So many people in the comment section have asked one same question, "what is the code???"
well I have figured it out.
first you will need to find and interact with all breaker boxes (or power boxes, whatever)
they are all marked in order therefore here are all the locations:

1: Main Power room, near tester.

2: Entrance closest to plane, near back corner.

3: Storage room near secondary entry farthest from plane, on the right wall when you enter.

4: Security/ comms room near secondary entry, next to a door.

After finding, and activating all breakers, there is a radio in the comms room that you need to pick up, that will repeat the code twice, but ONLY twice. afterwards it will play that really nice song.
I will leave you all to find out what is really inside that code-locked door.













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