A private light aircraft is certified for one crew, the pilot, with the exception of training where there may be another pilot (Instructor) on board.
Article 150 defines a passenger as any person other than aircrew.
The UK FRTOL is defined in Schedule 8 as a Flight Crew Licence however; ICAO Annex 1 no longer recognises a Flight Radiotelephone Operator as a stand alone flight crew member. The FRTOL is normally an endorsement to an existing flight crew licence to facilitate operation of the radio. The UK may be unique in issuing the FRTOL to persons who do not hold another flight crew licence; they must keep a log (Art 35) in order to record the experience necessary for revalidation but, as they are not required for the certified operation of the aircraft they cannot claim to be crew members and in accordance with Art 150 are passengers.