I know this is kind of a silly question, but I'm curious.

On a "standard" multi-engine airplane, the engines are numbered from port to starboard, with the furthest port engine being number one. But in a "push-pull" twin-engine airplane like the Cessna Skymaster, which engine is considered "number one"?

  • $\begingroup$ @757toga Well, who decided that the left engine is always "#1" in a conventional plane? $\endgroup$ Commented May 9, 2023 at 2:42
  • $\begingroup$ Probably some pilot or engineer from the early days who's name is forever lost to the sands of time... $\endgroup$ Commented May 9, 2023 at 2:46
  • $\begingroup$ With the port/starboard engine numbering, if they had copied ship numbering schemes we'd have even numbers on the left and odds on the right, just to really confuse people. $\endgroup$ Commented May 9, 2023 at 8:03
  • $\begingroup$ @757toga Listening to ATC recordings on YouTube and LiveATC, I've heard them refer to engines by number, even on twin-engine Boeings. They will usually clarify by saying something like "We're having trouble with engine number one; the left-hand engine". $\endgroup$ Commented May 9, 2023 at 13:44

2 Answers 2


If Cessna didn't designate them as #1 and #2, then there isn't one.

The convention Boeing uses is Left-to-Right and Front-to-Rear for numbering: the left engine is the #1, the forward doors to the aircraft are the #1 (1L and 1R) doors, and things work toward the rear from there (2L and 2R, then 3L and 3R, and so on). And obviously seating rows start with #1 in the front and get ever higher numbers toward the rear.

So by that convention, the forward engine would be the #1, which would probably be intuitive to most people.

Interestingly, Lockheed used the same front-to-rear convention for numbering the guns on the AC-130, where the #1 and #2 were the twin 20mm cannons up front, and stepping up to higher numbers working toward the rear. In the AC-130U, which didn't have twin 20's but a single gatling gun up front, that gun was the #1, the 40mm was the #2, and the 105mm was the #3; in the older AC-130H I think they didn't renumber things as the small gatling guns were removed, so I think they still referred to their 105 as the #7 gun, even though there weren't 6 guns installed forward of it. I assume that the AC-130J uses the same convention, but I'm not familiar enough with those to state anything definitively there.

  • $\begingroup$ Good answer., but at least in the B737 ck list it normally refers to engine #1 and engine #2 (when starting for example). The C337 ck list only refers to "front," "rear," and "affected" engines. $\endgroup$
    – user22445
    Commented May 9, 2023 at 16:50
  • $\begingroup$ @757toga Yeah, thus my first sentence -- if Cessna didn't designate a #1 or #2 engine, then there isn't one, period - dot - full stop. Everything after that is just what-if-ing and "if you were to apply the Boeing or Lockheed conventions to this Cessna, here's the result you'd end up with." Not suggesting that there's a reason to apply those conventions there. $\endgroup$
    – Ralph J
    Commented May 9, 2023 at 18:32

In this 1971 Cessna 337 Skymaster (push-pull twin-engine airplane) Owner's Manual the engines are referred to as the front, rear or affected, depending on what section of the manual you are reading.

I'm unaware of a specific, universally accepted designation, that identifies a Skymaster's engines (push-pull twin-engine airplane) as "number one" or "number two."


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