jaja,
well as usual there many controversial issues. This is just one of them and in many cases subject to personal interpretation of the commander. However the lawmaker must define the point at which he considers the aircraft to be dispatched and this is moving under its own power for taxi under JAA. The necessity for definition of the dispatch point is obvious as you it represents the transition from preflight to flight phase with associated applicable rules. Lets take an example Minima for DEP ALT Airdrome. For planning purposes you must take higher minima if DEP ALT is required, and this condition must be fulfilled until the dispatch of the aircraft. Once you moved on your own power for taxi only the applicable minima applies. The same would be with fuel policy. In general one can say that its intention of the JAR's to separate the phases in to preflight and dispatch or in-flight, ergo you need a point and that's moving under own power for taxi under JAA. Whether it makes sense or not its up to PIC judgment and as stated above if the PIC isn't happy he always can go back.
Cheers.
