Question for CrowHunter....
Worst case scenario 777 enroute to Hawaii engine goes out 1,000 miles off shore, how is fuel consumption/range affected when flying on one engine?
In that scenario what would be the best altitude/speed for conserving fuel?
Your optimum altitude is dependent upon several things, winds and the weight of the airplane being the biggest, we try to cruise near the optimum altitude for fuel efficiency. If you lose an engine at cruising altitude the airplane won't maintain that altitude single engine, you're going to have to descend. The optimum single engine altitude and airspeed, we call them driftdown, are going to be lower and slower. How much depends on weight and winds. Generally with the 777 if you're at 35,000' or so and you lose an engine you'll have to descend to the mid 20's and slow down some. The exact numbers were determined by Boeing when they conducted all the test flights, there are charts for it and it's built into the FMS, the aircraft's computer. You'd go into the FMS to get the altitude and airspeed then descend and slow to what it calls for.
It's going to burn more fuel for a couple of reasons, the first one being that you're lower and that always burns more fuel. Secondly you've now got a dead engine hanging out there that's costing you drag, plus the asymmetric thrust means the rudder is going to be deflected some to keep the plane in balanced flight which means more drag, more drag takes more fuel to overcome.
ETOPS flight plans are built around an ETP (equal time point), that's a point between the two alternate airports that's halfway timewise between the two. It's not half the distance (unless there's no wind), it's based upon flight time. That ETP is the most fuel critical point for an engine failure to occur, if an engine failure happens there then that's where you'll have the longest time to go to get to an alternate airport. The fuel planning is very complex and done by computer, one of the things it looks at is the required fuel if an engine failure happened at the ETP, it'll calculate how much fuel is required to driftdown and get to an alternate with the required reserves of fuel. The flight won't be allowed to take off unless it's carrying enough fuel to fly from takeoff to the ETP, lose an engine, then driftdown and make it to the alternate with sufficient reserves. Since the ETP is the worst place fuel wise for a failure to occur, any place either side of that means you have more fuel than you need. In your hypothetical scenario of losing an engine 1000 miles offshore enroute to Hawaii the flight would have left it's departure airport with enough fuel for that to happen and proceed safely to it's alternate airport, they couldn't legally take off without the fuel for it.