This has been going on for a long time now, and I don't think anyone's really tried to fix it. Most of the new Navarro content is completely broken from what I've played. Maria's dialogue loops, the toxic caves quest not being able to start at all, and of course the Vertibird now only featuring...
I encountered a pretty nasty bug with the Vertibird mod on version 2.47.4.2. Trying to travel with it to places resulted in a black screen which i could clear up by hitting F1, but the Vertibird was missing. I decided to go back to Navarro to see if it was still there and the rear part was out...