Each engine is entirely independent of the other. The chances of two quitting during the same flight are one in several million.
8 seconds sound clip from the The High and the Mighty (1954) movie soundboard.
You can hear this line at 00:31:39 in the DVD version of the movie.
Quote context
[...]
- Suppose one of your motors ceases to function?
- We'd just go back to Honolulu.
- These ships fly beautifully on three engines.
- If it should happen beyond our point of no return, we'd simply continue on to San Francisco.
- Well, suppose two of your motors became uninterested in further toil?
- Even if that should happen, we could still fly, lower and much slower, but we'd get there.
- Why is it I read about so many crashes?
- The newspapers always exaggerate the importance of an air accident.
- It would be very important to me if I were in one.
[...]