
Cosco Kids
Scenera Next DLX Convertible Car Seat
Super light, cheap, great for air travel, but outgrown fast.

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What seat is she in normally? I just flew with the Graco Tranzitions, which is FAA approved in harness mode. The WayB pico might be an option. I think it has quirks based on your child’s size though
Graco transitions has a high back forward facing with straps, it starts at 22lbs and goes up to 49inches. So she would fit in it ET: It's what my 5 year old who is tall and skinny uses. Fits him great
We went from infant seat to extend to fit to Graco transitions to a cheap booster. But that's mostly because there was a sibling to use the next seat. Transitions can also be a backless booster. They didn't make rotating seats when my oldest was little so I never tried one.
The Graco Tranzitions is pretty lightweight, and it’s a 3-in-1 FF 5pt/HBB/no-back booster, so after the trip you could save it for later when he moves to a booster seat. Since it transitions to a no-back booster, you can take the back off to make it much shorter — so if you end up not having him sit on it on the flight, you could probably fit it into a carry-on bag for the plane, then put it back together at your destination.
Pretty easy. I’d say <2 min each to take it apart and put back together. The manual has you take the harness straps all the way out when taking it apart since they’re assuming you’re about to use it in booster mode, but I don’t think you’d have to 100% uninstall them just to take the pieces apart. I can take a look at it tomorrow and measure how compact it can get when apart.
i’m 5yr into the carseat game. the UB mesa was awesome/easy and we’re on our second graco (slimfit and now the big kid one). it’s under $200 and very safe. kept my kid RF until after age 5!
When we for with our 20 month old we used the Evenflo Tribute LX. She was right at the edge of there weight limit, and maybe a lb or two over fully clothed and stuffed with food. But it worked really well for us. It’s only 9.3 lb so relatively lightweight. My husband was able to use a heavy duty caribeaner and hook it upside down over his backpack so our hands were free. We tried the either Cosco Scenera or Maxi Cosi Romi (I can’t remember which, but they’re basically the same car seat, made by the same megacorporation but under different brand names and Maxi Cosi has nicer fabrics) because it was lightweight and highly recommended for travel. She was right at the weight limit for it (40 lbs), too, but we weren’t able to use it because the straps were comedically too short. Like I don’t think they made it even halfway around her body. That might not be an issue for you, if yours is tall but not wide. Mine was super off the charts heavy and not particularly tall. All to say check the height restrictions, and make sure you buy far enough in advance that you can return it and buy another if you need to. Or plan to buy two and return one. Because you don’t want to buy too far in advance and then they outgrow it by the time the flight comes around. Now that she’s older (3) we like the Graco Tranzitions 3-in-1 for travel. It’s also lightweight. But it’s forward facing only, so not really suitable for a 1 year old.

Cosco Kids
Scenera Next DLX Convertible Car Seat
Super light, cheap, great for air travel, but outgrown fast.

Cosco Kids
Scenera Next Convertible Car Seat
Portable, affordable, quickly outgrown, airplane buckle discomfort.

Joie
Mint Latch
Easy baseless LATCH install, lightweight, but quickly outgrown.

Nuna
PIPA Series
High-end travel, easy baseless install, but very pricey.

WAYB
Pico™ Portable Car Seat
Ultra-light, compact travel, quick install, but expensive and outgrown fast.

Ranked #1
Cosco Kids - Scenera Next DLX Convertible Car Seat

Ranked #1
Cosco Kids - Scenera Next Convertible Car Seat

Ranked #1
Cosco Kids - Scenera Next DLX Convertible Car Seat

Ranked #1
Doona - Doona Series

Ranked #1
Cosco Kids - Scenera Next Convertible Car Seat

Ranked #1
Nuna - PIPA Series