Not sure why I need to know this, but it's on a gouge sheet for an interview and I can't find the answer anywhere...
1.) "It is perfectly legal to fly in UNCONTROLLED airspace without and IFR flight plan or clearance. In fact, no clearance is required (or even possible) to operate IFR in Class G airspace. Therefore, when receiving an IFR clearance on the ground at an uncontrolled airport, the clearance will usually include the phrase "upon entering controlled airspace..." (91.173). You are, in fact, operating in Class G without a clearance until you get above to 700-foot transition altitude EVERY TIME you take off with a void time! Your IFR clearance does not actually begin until you enter the Class E airspace."
2.) "91.173 states only that "no person may operate an aircraft in 'CONTROLLED airspace' under IFR UNLESS that person has filed a IFR flight plan, and received the appropriate ATC clearance." It says nothing about operating in UNCONTROLLED airspace, so the regulations does not apply.
3.) In UNCONTROLLED airspace, no flight plan or ATC clearance is required (or possible to get). You can still operateunder Instrument Flight Rules without a flight plan or any clearance from ATC. You must be instrument current and the aircraft must be approved for IFR flight. You must cruise at an appropriate IFR altitude (91.179), adhere to minimum altitudes for IFR flight (91.177), and comply with the other IFR requirements of 91 subpart B that apply to IFR such as fuel reserves and VOR checks, however he altimeter, ModeC and static system checks of 91.411 need NOT be current."
4.) "You do NOT have to maintain cloud separations (in Class G) because the flight is being conducted under Instrument Flight Rules, which do NOT require could separation."
5.) "Part 135 or 121 operators are NOT allowed to operate "IFR" in Class G terminal (airport) airspace UNLESS the airport has WEATHER REPORTING."
QUOTED FROM "EVERYTHING EXPLAINED FOR THE PROFESSIONAL PILOT-7TH EDITION" PAGE 7