N265QS is a Falcon 2000 and I’m guessing the GIV is in fact N465QS, but how can the FAA have accepted both plans ?
The FAA doesn’t validate tail numbers to see if they’re registered or against the registered aircraft type when you file a flightplan. We see typos like this (by operator or ATC) all the time.
Understood, but are you saying that two airplanes with the same id can be in the air at the same time without some software catching it ?
It used to be a routine occurrence before American Eagle upgraded from 3 digit flight numbers to 4 digit flight numbers. Still happens occasionally.