What? B777 is first delivered in 1995, and Cathay Pacific operates A330/A340 only since 1996 (though B777-200ER entered the market since 1998.)

Air France uses nothing other than GE engines and CFM engines, which is a 50 / 50 joint venture between GE and Snecma of France. But there is no GE engine option on A340-500/-600, and GE engine is the sole engine of B777-200LR/-300ER, so Air France goes for B777-200LR/-300ER instead of A340-500/-600.

Even so, some airlines that use mainly GE engines on its aircarfts, like Iberia, China Eastern, go for A340-500/-600 instead of B777-200LR/-300ER, but there is NO airline uses mainly Rolls Royce engines goes for B777-200LR/-300ER. This proves the quad-engine design of A340-500/-600 is better suited for long haul routes, especially the routes over the extreme areas.

If there is GE engine option for A340-500/-600, then Air France would certainly go for A340-500/-600 instead of B777-200LR/-300ER.

Singapore Airlines does not use GE engines, and uses only Rolls Royce engines on its B777, and there is Rolls Royce engine option for B777-200ER. So Singapore Airlines goes for B777-200ER. But there is no Rolls Royce engine option for B777-200LR/-300ER, so Singapore Airlines goes for A340-500 instead of B777-200LR.

If there is Rolls Royce engine option for B777-200LR/-300ER, then Singapore Airlines may go for B777-200LR instead of A340-500.

All these shows how engine options of an aircraft governs the fleet selection so much!

If there is Rolls Royce engine option on DC-10, then Cathay Pacific would go for DC-10 of much larger capacity, longer range and better economy instead of very poorly designed L-1011, which Rolls Royce is its sole power!