I have not flown with this pack, but I do travel a lot for work and on those small regional jets. I have seen people travel with similar sized packs so I think you should be fine, as long as it fits in the over head compartment.
I’ve used mine before. Never said a word about the size of it and I had that thing packed to the brim. But depending on the size of the overhead bin it may not fit. On smaller commuter type jets it probably won’t fit. Happened to me before and they just gate checked it. On the bigger planes it was all good
Check the policy and size regulations with the specific airlines you are flying.
I wont try and generalize when it comes to flying as the airlines are all different.
I have carried mine and 1) Had zero problems, and 2) Had big problems. You never know when the gate agent will make a point with your bag...
Tips from my experience:
remove the belt and pack it in the bag or WEAR it.. The belt makes the bag LOOk physically larger/bigger
Remove the brain/lid and either use it as a personal item, or store it in the bag, it also makes the bag LOOK big.
OR, ignore the above and run into problems at some point where you are planning to board and facing a difficult choice of having to check your 3500 and all the optics and electronics you have in it.
I have flown my pack 5 times with out issues. However I am always prepared to gate check it. Pack it to the brim and remove the belt, it will fit in the overhead bins on commercial airlines. I always ask the gate agent up top how full the flight is and let them know I'll gate check if needed. You shouldn't run into any issues if you anticipate things and are flexible.
I plan to take mine too next year. I'll be flying Alaska Air the whole way. I hear they are pretty lenient and they seemed that way on my last trip, That trip I had my pack in a Kuiu Taku bag and checked it, had my optics in a Taku 2000 for a carry on. This time I'm thinking of going with a checked tote of gear and the Exo 3500.
Alaska Airlines is a little too lenient about carry-on size. The majority of their flights I’ve been on they’ve asked people to volunteer to have their checked bag checked at no charge because the overhead bins were to capacity.
I’ve seen guys walk onto Alaska airlines planes with 5000 to 7000 in.³ bags and practically their full kit, like they were going to get dropped at the base of a mountain in a 737.
United and Air Canada on the other hand will regularly make people put their bags in their little cubicle to see if they fit and will also flag you if you’re over there 15 pound carry-on limit.