5
$\begingroup$

It is well known that planes with two engines must be able to land with one engine inoperable for their certification, and that four engine planes with two inoperable.

Now, suppose you had a four engine plane with 3 engines inoperable, and only one remaining. In terms of the greatest likelihood of survivability of this incident, is it at all favourable to have the engine closest to the body of the plane active, or the one further out?

As far as I can see it, there are two main ways to tackle this; one is by looking at incidents where triple engine failure occurred (which is very rare) and seeing whether it makes a difference.

The other approach is how does it affect the controllability and maneuverability of the aircraft theoretically or based on testing depending on if one has the jet engine closest to the body active, or the one further out on the wing. It may be that the difference is negligible, but I'd be curious if there can be some argument made to favour one option.

There would be other variables to take into account, so to narrow it down a little more, I am considering only jet engines, on aircrafts used for commercial flight.

Improve this question
$\endgroup$
6
  • 3
    $\begingroup$ The yawing moment will be higher if the outboard engine is operating, but during certification, flight is demonstrated with both engines on one side failed (therefore both engines on one side working) which would be an even higher yawing moment than the single engine working. My short, intuitive reasoning (not really an answer) would be that it shouldn't make a difference if you have a well-trained crew who doesn't let the yaw get away from them. $\endgroup$
    – Lnafziger
    Commented Mar 30, 2017 at 16:19
  • 1
    $\begingroup$ @Lnafziger Thank you for introducing me to the terminology too ('outboard engine') - I was sure there had to be a word for it! :) $\endgroup$
    – user1997744
    Commented Mar 30, 2017 at 16:28
  • 1
    $\begingroup$ Like lnafziger said, the outboard engine has a longer yawing moment. So if you had your choice you would choose an inboard one $\endgroup$
    – TomMcW
    Commented Mar 30, 2017 at 17:25
  • 9
    $\begingroup$ It's a minor point, but one of the rules is to avoid turning into a dead engine. Thus, assuming the captain will be flying the aircraft in such a situation, I would choose to have the inboard engine on the left side running. That way in maneuvering for a landing I would have the better visibility on my side in the direction of the turn while avoiding turning into the dead engines side. $\endgroup$
    – Terry
    Commented Mar 30, 2017 at 17:53
  • 1
    $\begingroup$ @Terry These are all good responses and sufficient to be answers. $\endgroup$
    – user1997744
    Commented Mar 30, 2017 at 18:08

1 Answer 1

Reset to default
5
$\begingroup$

Using the inner engines allows you to maneuver easier as the yaw moment is smaller in comparison to the outboard engine which also means you need less rudder inputs to keep the course. The big advantage of needing less rudder to keep a straight path of flight is that you can react better because the rudder can move a bit more.

Which sides engine to use is depending on the wind situation (I would use the engine on the side the wind is coming from as you can turn into the wind better to keep your course) and other influences like if you need to turn left or right more often; avoid turning into a dead engine as Terry already mentioned).

Improve this answer
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .