Originally Posted by Qtip

In regards to your question in bold:
I don't think that an empty aircraft in your example necessarily is a Part 91 flight. Lets assume that someone, for some odd reason pays a 135 operator to fly an aircraft without passengers or cargo. The flight is paid for, regardless of what or who is onboard. It must then be flown under Part 135. Another example: A charter company in LAX is paid to fly a passenger LAX-PHX, drop him/her off and then return empty. The passenger was quoted, and charged for the airplane to return to LAX. Although the aircraft is "empty" someone paid for it to return to LAX and it is then a revenue flight and must be operated IAW Part 135.