[Someone]

> They'd have to show at least one plane with a bearing gone that still flies as intended.

That depends on the meaning of “safety of flight”. I don’t know what it means in aviation, but do not rule out that there is significant room between “flies as intended” and “result in a safety of flight condition”.

For example, if an engine were to complete drop off the plane, would that necessarily result in a safety of flight condition, or does “the plane will be able to continue take off and land again” mean safety of flight isn’t affected?

[ethbr1]

Some of it may be related to the 3-engine design, if Boeing had modeled that 2 engines still provided sufficient power in all scenarios.

But a takeoff does seem like the worst time to catastrophically lose 1/3 power, even without FOD intake by the central engine.

[foldr]

Certainly two engines would provide enough power in all scenarios, including take off. That’s a fundamental safety requirement that any airliner meets.