maui,
Navigation / Etops 101 .....
Great Circle route is the most direct track between any two points on the planet. In this case, this route Mel-Jnb is not an approved Etops route - it carries a twin too far from an adequate airport (they have to remain within 120 / 180 / 207 / 240 minutes at single engine speed in still air from those airports).
So, the 747 can fly the great circle route in this case, but the 777 cannot - it must fly a longer route to keep closer to an adequate airport (in this case Adelaide / Perth / Mauritius / Durban). Of course an important point here is what Etops approval V will have for their aircraft. 180 min is pretty standard these days, but 207 or 240 min are new for Australia, and ANY Etops approval requires a lot of work on the part of the Airline.
So, the point is, how much longer is the route the 777 will have to fly to get to Jnb, and what impact will it have on its operation? Both the 747 and 777 fly direct, it is just that the 777 cannot avail itself of the shortest route.
I trust that clears up your mis-understanding ...
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