Two-engine aircraft are designed to deal with the loss of any engine without danger. My question is whether a four-engine aircraft that is missing one will still have the safety margin of being able to withstand the loss of any other engine without danger. And asymmetrical thrust is my concern; on a 777, the engines are all located near the central axis, so the moment generated by assemmetrical thrust would be somewhat limitted. I would expect that on four-engine aircraft, the moment generated by using two same-side engines would be greater. Cutting back power on the outside engine could reduce this moment, but I don't know how much spare thrust is available. To be sure, I wouldn't expect the plane to fall out of the sky with two engines (since maintaining flight should require a lot less thrust than taking off) but I would think controllability would suffer greatly.
And four-engine aircraft are designed to deal with the loss of any engine without any danger.
Two-engine aircraft are designed to deal with the loss of any engine without danger. My question is whether a four-engine aircraft that is missing one will still have the safety margin of being able to withstand the loss of any other engine without danger.
Listen to yourself! Are you not equally concerned with a two-engine aircraft losing another after losing one? Why not? Why do you consider it perfectly safe for a two-engine plane to lose one engine but not for a four-engine plane to lose one engine? You say "but what if it lost another"? Well, what if the two-engine plane lost another? That would concern me a heck of a lot more. But you simply dismiss it with "Two-engine aircraft are designed to deal with the loss of any engine without danger." But so are four-engine aircraft. You seem totally irrational.
To sum up your argument: it's a disaster for a four-engine plane to lose an engine becasue it might lose another and then it would only have two engines left even though it can still fly with two -- but that's a disaster. But for a two-engine plane to lose an engine, that's hunky-dory because they are "designed that way" and if they lose one they could never lose another even though that would leave them with NONE -- and that's perfectly safe.