Ответ:The Without-Crew model (PSE P/N 11922) has a center selector switch with a position labeled Iso* that allows the pilot to isolate himself and the radios from the other 3 intercom stations. While the With-Crew model (PSE P/N 11920) has a center selector switch with an additional third position labeled Crew which allows both the pilot and co-pilot positions (collectively the front seat flight crew) to isolate themselves from the back seater allowing the front seaters to converse with each other and transmit on the radios without the distraction or interruption from the back seaters. So it essentially comes down to whether the aircraft owner wants the pilot to be able to isolate himself alone or add the additional option of being able to isolate both front seaters as a Crew. Obviously there would be no reason to have the crew model in a two-seat aircraft. The jack wiring is also different between the two models so the harnesses are not the same.
