No one builds a radio receiver (1/2 of an altimeter) with perfect total out of band frequency rejection. Physics does not work that way. Frequency may be modulated digitally but it is in fact not digital. You build good enough. Now thanks to FCC good enough is no longer good enough.
Proving safe requires testing all versions of antennas, altimeters, Cell equipment in real world environments to show mutual compatibility. Just pray that there will not be two or three crashes before the world figures out there is a problem.
Space Shuttle crew members 5, 6, 7 had no launch or flight responsibilities as they were not seated on the flight deck. In the event of a controlled flight bail-out they would have been responsible to get the door open et al.
This past March on a SW flight from ATL to RIC, after we boarded the piolet announced they needed to move weight from the back to the front. Departure was delayed while three carts of baggage was moved from the back to the front. I saw our checked bag get loaded during that process.