The crew found a stowaway.
Stowaway = “blinder Passagier” in German (literally “blind passager”): dict.cc | Blinder Passagier | English Dictionary
I was unable to find an explanation for this one online. It seems like an odd way of describing someone who didn’t pay for a ticket.
An old meaning of “blind” was “heimlich” (secretly) or “ungesehen” (unseen).
This meaning from the 18th century survived only in “blinder Passagier”.
Thank you. I was trying to think of an English equivalent, but all I could come up with is blind man’s bluff or a blinded experiment. But that’s “blind” in the usual sense, not like this usage.
A “blinder Passagier” isn’t just someone who didn’t pay for a ticket, it’s someone who - matching the old meaning of “unseen” - hides in the cargo bay or something, and no one knows they’re there.
If you just don’t pay the ticket, then you’re a “Schwarzfahrer” (verb form: “schwarzfahren”), which dict.cc says is a “fare-dodge” in english.
Also, I wonder if other “blind”-related words such as “Blindabdeckung” come from the same old meaning. 
Interestingly, dict.cc also says that “Blinddarm”, which is usually translated as “appendix”, is also “blind gut”.
I thought of one in English, though it’s a bit obscure: Houston in the blind, as heard in the movie “Gravity”, with Sandra Bullock. It means “I’m speaking to you but I can’t hear your responses, so I don’t know if you can hear me or not”. In that sense, I’m “blind” in the sense of possibly being hidden from you. This is pretty close to the use of blind in the German expression “blinder Passagier”.
And yes, “schwarzfahren” does indeed refer to fare-dodging in English, though I think the German term for it sounds cooler 
Your example and this confusion of “not see” and “not be seen” reminds me of when little children try to hide by covering their own eyes, thinking that if they can’t see, then they also can’t be seen.
The crew found a stowaway.
A ‘blind’ is a hiding place for a hunter. The hunter can see the animals, but the animals can’t see the hunter.