Guillermo wrote
There are many unclear parts in the FAR where there are different
interpretations among pilots. However, I would say that 99% of the
pilots would agree with the interpretation that anyone who is not a
required crewmember in an airplane is considered a passenger.

I must be the 1% that knows better.

First, posters in this thread are not distinguishing between the
definitions in Part 1 for "crewmember" and "flight crewmember".
There are several categories of individuals aboard aircraft that do
not posess airman certificates and yet are designated as "crewmember".

FAR Part 1
Crewmember means a person assigned to perform duty in an aircraft
during flight time.

Some of these are obvious....Flight Attendants, Medical Attendants,
Flight Test Engineers, Loadmasters and even "Grooms" accompanying a
load of racehorses are listed on the manifest as "crewmembers". It is
common for airlines to staff a flight with more than the FAA required
minimum number of Flight Attendants. Are they listed on the passenger
manifest? Of course not, they, although not "required crewmembers" are
none-the-less, crewmembers.

Bob Moore
ATP B-707 B-727 L-188
Flight Instructor, ASE, Instrument
PanAm (retired)