We could take half the structural members out of a building and it will still stand. That is if you like to accept living in a building on the brink of collapse.
A plane with four engines has four engines for a reason. If one fails. The other three will still push it. If another fails, especially on the same wing, pray because you are on the brink.
This is a case where management chose increased risk for passengers. They lucked out. Those on the Challenger didn't when NASA's management made a stupid decision ignoring engineers' warnings and approving to fly below design temperatures.
By the way, British Air did not learn their lesson. The next day that same plane flew to India on three engines.
The flight from LA just barely made the British Isles as they were running out of fuel. They didn't make Heathrow. I wonder if the engine that failed on the way to India had failed a day earlier, if that plane would have made even Ireland. The FAA should bust BA's cookies.
The same three, too - the replacement engine died after takeoff.
Oh, my that is NOT good.
How is crossing the Atlantic with three engines (a 747 with one out) any less safe than crossing the Atlantic with two engines (on a two-engine A310 or 777)?
One could probably take out half the studs in a typical residential wall without affecting the structural integrity of the building; the requrement of having studs every 16" is to allow people to lean on walls without them bending--not because it's necessary to support the weight of the roof or upper floors.
On the other hand, most buildings have many single-point entities whose failure would cause a significant partial or total collapse. Bridges are even worse: a failure of one of the main cables on a suspension bridge could topple the whole thing. Of course, most of the single-point-failure items are rated to withstand loads sufficiently in excess of the loads they'll face that failure is unlikely.
This sounds like the same thing that happens whenever a "cost control" culture takes over a major corporation. Employees who are afraid to spend money, no matter what the circumstance, end up making dangerous, short-sighted decisions.
I'll bet the CFO of British Airways is going to have some explaining to do to the board of directors.