The list author says: "Traveling with young children often also means traveling with the bulky car seat or booster seat. Not all child restraint systems are allowed on airplanes, and some are designed specifically for the airplane.
My son was kept safe when flying by the FAA approved 1 lb. CARES harness created FOR airplane seats (children between 22-44lb.). This was only for aircraft use, but was great for those times when I had a car seat at the destination or in Europe where I used trains and planes exclusively for transportation.
For car seats that travel well on aircraft, I have relied on the advice of pediatrician and "Car Seat Lady" Alisa Baer, M.D. when deciding which car seat to travel with domestically and internationally.
I have listed the CARES harness as well as car seats for aircraft AND booster seats (automobile use only) that she recommends. Please note booster seats are not allowed to be used on airplanes. I also have added some of my personal favorite car seats as well - keeping ease of installation, fit in cars and planes, as well as comfort in mind."
"Car Seat Lady Alisa Bauer, M.D. recommends this car seat/stroller combo for airplanes and taxis for children up to 40lbs.. However, she notes it may be cumbersome to use as children are required to be seated during installation and removal of the car seat."
"The Traveling Toddler is a fun, lightweight product to transport heavy car seats through airports! The little strap uses the LATCH system and attaches car seats onto luggage (for transport use only- not for safety). A few years ago, I uploaded a video on YouTube of the Traveling Toddler accessory in use (my son enjoyed the ride!) YouTube: http://www.youtube.com/watch?v=TCumQgsXWU4"
"Big and bulky - but I loved it for checking the car seat as baggage! (I use the CARES harness for airplane safety) This bag was great for checking the car seat and hauling it around like a backpack. Warning - you stick out far - but it is a bulky car seat so it's somewhat expected!"
"We used the 1lb. Bubble Bum on our 20 country/4 continent/8+month world tour! Approved both inflated and deflated, this backless booster is fantastically convenient for taxis and rental cars while traveling! (not for use on airplanes) The booster provides protection by holding the vehicle seat belt in the proper position for older children."
"Narrow (great for airplane seats and fitting 3 car seats in the backseat of a car), folds in half for transport, and can be worn like a backpack. These seats are heavy (steel alloy frame) but not horrible when slung over stroller in airport or worn as backpack."