Is the most fuel-efficient route between points A and B always along a great circle ?
Although somewhat counter-intuitive, this comment on an aviation blog seems to suggest that longer paths (in terms of geographic distance covered) can save fuel:
Oceanic Flights these days are not restricted to the old “defined great circle routes”. Modern computerised flight planning systems definately take weather into account, and go searching for the best winds (tailwinds) or least adverse (headwinds). Particularly in the case of westbound flights across the Indian Ocean, where headwinds are often ferocious, the tracks actually flight planned, and actually flown, are often a long way off “great circle” routes.