Just blundered in here!
Just my two pennyworth. Luftwaffle is adamant that the defining item for an IFR flight is the flight plan.
Regrettably I don't have my library with me - all in a foreign land at the moment!
However, in South Africa a flight plan does NOT have to be filed for a flight under IFR. And I would be prepared to bet a good few drinks that this is NOT an ICAO departure!! (I certainly can't recall it as being such, whereas the UK quadrantal rule, for example, is very much an ICAO departure!). There is no problem flying IFR between unmanned fields in SA without a flight plan as long as the normal legal minimum heights, cruising levels, minimum equipment etc requirements are adhered to.
I appreciate that, in the UK, for example, you are unlikely to fly under IFR without going into controlled airspace, which is going to need that flight plan; some countries are a bit bigger and more deserted - I would have thought Canada would be one!
Of course, one would be a bit daft to go off into the bright blue yonder without filing a flight plan, but my concern would be the SAR!
I would dearly like to give a definitive answer to the original question, to fit all countries (if possible), but all my stuff is overseas. South African Air Law has been recently revised and is VERY closely modelled on the JARs. From memory (and I did have to answer this quesion once) the problem is that the legislation refers blithely to flight under the Instrument Flight Rules without actually defining "the rules". One then has to do the legislation hop-hop-hop to find what one is obliged to do if flying under IFR. These tend to be scattered (hence the hop-hop-hop), but include minimum enroute altitudes, cruising level, minimum equipment, flight planning as to fuel, alternates etc.
So, my little input is: "flight under IFR is flight under the legislative rules that must be followed if the flight is to be conducted under IFR."
A bit circular, but I reckon that's it. And, at least in SA (and I think ICAO), not a flight plan in sight.
My definition is not as daft as it seems. Remember that if you are flying from Toronto to Cape Town, or Bombay for that matter, the flight might be under IFR, but the rules can CHANGE as you enter the airspace of different states, who have different rules to be followed for an IFR flight, eg flight plans required in Canada! So what we need is a definition that can encompass a variety of changing rules.
God, I wish I had never looked in the Canada forum!! I feel a bit like a trespasser; sorry guys!
[This message has been edited by GRpr (edited 05 May 2001).]
[This message has been edited by GRpr (edited 05 May 2001).]
[This message has been edited by GRpr (edited 05 May 2001).]