Hi, again Oldghm,
Here's what I found.
What size is carry on luggage?
This isn’t always an easy question to answer because carry-on luggage size varies from airline to airline. So if you’re trying to determine what size luggage is carry on, you’ll need to look at the airline you’re flying with. Lucky for you, we’ve put together the most comprehensive carry-on size chart on the internet with over 170 airlines from around the world. Check it out below!
What is TSA carry-on size?
Just as there is no one standard carry-on luggage size, there is no TSA carry-on size. Your carry-on bags must fit through the X-ray machines, although the exact size of the machines may vary from one airport to another. Follow your airline’s rules about what size carry-on luggage they allow, including other airline carry on luggage rules such as luggage weight and number of items allowed. Check out our carry-on luggage size chart below for more info.
Without a case, the S1 Pro with battery is about 16 pounds, and the dimensions are 13" H x 9.5" W x 11.2" D.
From what I've read here and there, the S1 Pro is probably too big (9.5" dimension) to fit under the seat on most planes.
As for carry on, it really depends on the airline. Some go by the total number of inches of the baggage (e.g. 45" linear) The S1 Pro comes up to 13 + 9.5 + 11.2 = 33.7 (without a case). If measured that way, you're probably fine. I fly with my Composite Acoustic Cargo and it exceeds most of the measurements in the chart on the linked page. The linear size is close to 65" in the case, and I've never been asked to check it as baggage.
Here's another take on this. If you are only allowed one piece of carry-on luggage and a personal bag, if you're travelling with a guitar as your carry-on, you'd have to treat the S1 Pro as checked baggage.
If you're planning to fly with your S1 Pro, I'd call the airline before going to the airport. The airline has the final say in this.
I'll do some more digging and let you know if I come up with anything interesting.