Hi, im new here. My fiancee and I are going to be hiking in Yellowstone this july and we dont want check any bags in the airport because we are traveling from Puerto Rico and we will make a few stops, last month I traveled to NYC non stop and the airline sent my bag on a diferent flight and I dont want that to happen here. So thats why im looking for a hiking backpack that I can take in the plane with me as a carry on, also I want to take it with me while I hike yellowstone so it would be great if it had the rain cover just in case. The carry on size limit on most airlines is 22" x 14" x 9" or 56 x 35 x 23 cm

Not sure if your looking for a day pack or a something for multiple overnight use. We have been flying off to the NP's for years now and have had a few 40 liter sized packs. They fit well inside the overhead storage bins. We have Deuter act lite 40+10's that will work if not using the expansion sleeve.
The size listed by the airlines is very accurate for carry on luggage. We will day hike with the packs as well as use them for carry on's because we don't want to bother with another pack. We usually take a few more items on a hike in territory like Yellowstone than for local area hiking. We were hammered by a thunderstorm passing directly overhead last time there and were glad to have full set of rain gear. That was one I will never forget. Make sure you buy your Bear spray and have a wonderful time. Yellowstone is our favorite, you will love it.

jimmyb

Keep in mind, the other thing you can do is not put as much in a larger backpack and take a small suitcase as your second carry on. I've carried on my Baltoro 75 before, tied down to be smaller than my 40. I'm in the market for a new (lighter) backpack right now, have a look at my thread about them right right below this one. There have been some pretty good suggestions.

Pretty easy to find a liteweight backpack that will fit in the overhead compartment. Many of the ULA packs, the Six Moon Designs Swift, even older Mountainsmith Ghosts fit in the overhead. Check the ULA website and they should have the dimensions. Problem is, can you fit all your gear in a carry-on pack?

A pack by Z-Pack will certainly fit. You have to have your contents down to an appropriate level, though. Also, there could be other issues besides size: Sharp items (tent stakes?) and burnables (fuel, matches?) may not be welcome onboard.

If you're close to ultralight (<10 lbs base weight) pretty much anything should work. I've carried on a large Golite Pinnacle with a week's worth of food (my base was almost 12 lbs). It could fit in some overheads (ie, 737) that way but not others (little regional planes) so I stuffed it under the seat. Had my one change of clothes in my laptop bag that I left in a locker at my destination.

Forgot to mention no need for a rain cover. Put your critical items (sleeping bag and sleep/puffy clothes) in trash compactor bag and other items you need to reach easily (eg, electronics) in ziploc.