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Given the trend in the industry to move towards aircraft with two engines, could it ever occur that we see an aircraft manufacturer develop an airliner with just one?

I'm suspecting the answer is no, given the redundancy offered by a twin engine configuration (e.g. if the independent probability of engine failure is one chance in a thousand, the probability of dual engine failure is one in a million.). I know the Virgin Global Flyer used one engine (https://en.wikipedia.org/wiki/Virgin_Atlantic_GlobalFlyer) presumably because the risk of engine failure was acceptable given the task in question.

However, if someone were to manufacture an engine with a probability of failure below, say one in 100 million, could this configuration make sense from an economic perspective?

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    $\begingroup$ I replaced your references to "commercial" with "airliner" because commercial operations with single engine aircraft (C208, PC-12) are already ubiquitous, and the body of your question explicitly and implicitly referred instead to airline operations. $\endgroup$
    – J W
    Commented Jan 8, 2019 at 10:50
  • $\begingroup$ Great, thank you for the correction. $\endgroup$
    – Terry Lennox
    Commented Jan 8, 2019 at 11:09
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    $\begingroup$ Welcome to the site @TerryLennox, and thanks for the question. Unfortunately this question at the moment is opinion based, and is too broad. Could it happen? Sure, why not, if you had an engine that reliable I'm sure it would be used. Will it happen nobody can truly say. $\endgroup$
    – GdD
    Commented Jan 8, 2019 at 11:43
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    $\begingroup$ In Soviet times, Aeroflot operated a large number of single-engine Antonov biplanes. If Wikipedia is to be believed, ex-Aeroflot Antonovs are still transporting passengers in Asia and South America... Many ex-Aeroflot An-2s have since found work with regional airliners across Africa, Central and South America, Cuba and southeast Asia. en.wikipedia.org/wiki/Antonov_An-2#Civil_aviation $\endgroup$
    – xxavier
    Commented Jan 8, 2019 at 14:03
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    $\begingroup$ @J Walters: How do you define "airliner", though? If it's "an airplane used in regularly-scheduled passenger operations", then those C208, PC-12s, and similar single-engine planes are airliners. $\endgroup$
    – jamesqf
    Commented Jan 8, 2019 at 19:54

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There are two major problems I see.

  1. Even if you have an incredibly reliable engine how do you prove it is incredibly reliable. I can't seem to find figures for the target IFSD rate for the current higher ETOPs levels, but I find figures for early ETOPs of one per one hundred thousand hours. Lets say you improve that to one per billion hours, how exactly do you demonstrate it's that low? fly for a billion hours? Thats a hundred planes flying for a thousand years. This is why redundancy is the route taken for many safety critical systems, you can argue that the individual components are merely very reliable and then argue that the chance of two of them failing at once is extremely low
  2. Where do you put the engine? If you have a single engine you want it on the centerline. That is not such a problem for props or low bypass turbofans, but it's difficult for high bypass turbofans.

Because of these two factors I doubt we will see airliners move to a single engine configuration unless we see fundamental changes in airliner design and regulation.

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  • $\begingroup$ Thanks for the answer, it's really interesting of course that it's not easy to site a high-bypass turbofan on the centreline, I know that trijet aircraft did this, but it caused a quite a few issues as far as I understand. $\endgroup$
    – Terry Lennox
    Commented Jan 8, 2019 at 12:37
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    $\begingroup$ In the era when trijets were a thing engines had much lower bypass ratios than they do today, so their inlets were much smaller. $\endgroup$
    – Peter Green
    Commented Jan 8, 2019 at 12:40
  • $\begingroup$ That makes sense, I can't imagine mounting a GE90 on the centreline! $\endgroup$
    – Terry Lennox
    Commented Jan 8, 2019 at 12:45
  • $\begingroup$ What about like the old DC's? Mount a turbofan up on the tail? $\endgroup$
    – Jon
    Commented Jan 9, 2019 at 20:47

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