5 ms·

That really depends on the minimal number of engines needed for safe operation. Say that you need 50% of the engines on the plane to be able to fly safely, the

by jfim 7y ago

That really depends on the minimal number of engines needed for safe operation. Say that you need 50% of the engines on the plane to be able to fly safely, then having more engines is actually safer. For example, supposing that engine failures occur 1% of the time, with four engines there are 3.97 three and four engine failures per million flights. For a two engine plane, there are 100 two engine failures per million flights.

apta 7y ago
There's correlation involved with other factors however. If I'm not mistaken, things like maintenance are relatively easier (and cheaper) on a 2 engine aircraft compared to a 4 engine aircraft. So we cannot consider failure rates as an abstract measure.
- jfim 7y ago
  I agree, and it's also very unlikely that engine failures are independent, since they're the same model, coming from the same manufacturer, and the same maintenance procedures. There's probably less drag from two engines than four as well.
  - WalterBright 7y ago
    Even if two engines have the same defect, it's highly unlikely they'd both fail on the same flight.
WalterBright 7y ago
Engine failure can be more than just quitting. It can catch fire and burn the wing, it can throw turbine blades around, it can shake itself violently. These can cause other damage to the airplane. It can even tear itself off, surge forward, fall back and hit the wing. These things have all happened. I remember a DC-10 that crashed losing everyone in it when one engine came off and took out the flight controls with it. Then there's the Sioux City crash where the compressor disintegrated and took out all three hydraulic systems. That's what I meant by "collateral damage". Doubling the number of engines doubles that risk. On the other hand, a failure that would take out both engines on a twin jet is likely to take out 4 engines. Failures such as running out of fuel, ingesting a flock of geese, and ingesting hail.

by jfim 7y ago

apta 7y ago

There's correlation involved with other factors however. If I'm not mistaken, things like maintenance are relatively easier (and cheaper) on a 2 engine aircraft compared to a 4 engine aircraft. So we cannot consider failure rates as an abstract measure.

jfim 7y ago
I agree, and it's also very unlikely that engine failures are independent, since they're the same model, coming from the same manufacturer, and the same maintenance procedures. There's probably less drag from two engines than four as well.
- WalterBright 7y ago
  Even if two engines have the same defect, it's highly unlikely they'd both fail on the same flight.

WalterBright 7y ago

Engine failure can be more than just quitting. It can catch fire and burn the wing, it can throw turbine blades around, it can shake itself violently. These can cause other damage to the airplane. It can even tear itself off, surge forward, fall back and hit the wing. These things have all happened. I remember a DC-10 that crashed losing everyone in it when one engine came off and took out the flight controls with it. Then there's the Sioux City crash where the compressor disintegrated and took out all three hydraulic systems. That's what I meant by "collateral damage". Doubling the number of engines doubles that risk. On the other hand, a failure that would take out both engines on a twin jet is likely to take out 4 engines. Failures such as running out of fuel, ingesting a flock of geese, and ingesting hail.