The Soloy Dual Pac apparently allows two engines to rotate one propeller -- here's a picture of it on an Otter:

Is this recognised as a centreline thrust twin engine aircraft, a "standard" twin engine aircraft or just an aircraft with a single engine for FAA certification? What about for pilot licensing?

  • 3
    $\begingroup$ I don't know the answer (and I'm not familiar with the Soloy Dual Pac), but isn't this situation similar to a twin-engine single-rotor helicopter, where two engines both drive the same rotor? Those are definitely considered multi-engine. (And the PT6 cores used in the Soloy Dual Pac are also commonly used in helicopters as the PT6B and PT6C variants.) $\endgroup$
    – TypeIA
    Apr 9, 2014 at 13:29
  • $\begingroup$ @TypeIA: I'd say it's even more similar to the Allison T40 - two power sections, two propellers (contra-rotating), but a single common gearbox, which was enough to have it considered a single engine. $\endgroup$
    – Vikki
    Mar 13, 2019 at 2:58

2 Answers 2


According to the certificate is a

Twin Power Section Turboprop

and, later, note 7: (emphasis mine)

This engine is certificated as a unit comprising two separate power sections with the capability of single engine operation with either power section alone in multi-engine airplanes. The unit is also approved as a single engine with either or both engines operating continuously.

No explicit remark is given about pilot licensing, but given the note reported, I would say that a licence for a single engine is sufficient.

  • 1
    $\begingroup$ To me the bolded section sounds like it's main purpose is to imply single-engine rating is sufficient to operate it. $\endgroup$
    – Jan Hudec
    Apr 10, 2014 at 7:24
  • 3
    $\begingroup$ @JanHudec I thought I wrote exactly that, haven't I? $\endgroup$
    – Federico
    Apr 10, 2014 at 7:30

Two engines with the crankshaft welded, would be classified as a single engine. But when both crankshafts are connected with "one way cluck", a pure bureaucrat would call it multi-engines. A logical person would ask, how different would be to fly an aircraft with the crankshaft welded as a single piece or interconnected with one way clutches?

Both would fly in the same way. We expect that an intelligent person would classify it as a single engine as far as only one control is used for both engines. A helicopter is different because it uses more than one control.

  • 1
    $\begingroup$ More than one control for what? $\endgroup$
    – Koyovis
    Jun 3, 2017 at 1:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.