I just traveled via plane with my tiny toddler (almost exactly your baby's height and weight) in the graco snugride rather than lugging around my Britax--its a great option. She was at the very max of the height and weight, but she still fit. I did not use the head support either (my car-seat installation tech told me it was not required...and that was when she was much, much smaller). I could carry her down the aisle in the seat, which I think was easier than lugging a convertible seat and having a flight attendant carry her or whatever, plus I was able to use my travel system through the airport, which made bringing her around easier. (I actually used a bungee cord to attach the infant seat to the handle of the stroller so that she could sit forward in the stroller and watch everything in the airport; I thought that would make her happier as we waited for her plane). Then, just as we were about to board, I loaded her into her carseat, installed it in my travel system, and wheeled it down the jetway. I left the stroller on the jetway by the door of the plane (gate checked it), and then carried her on in the car seat--it worked really well! If you have a travel system to use, check to make sure that your airline will gate check your stroller. I was flying American Airlines and just after I flew they changed their policy so that larger strollers had to be checked under the plane--they could not be gate checked. I did not bring the base along and just installed it without the base using a seat belt in my brother's mini van while I was visiting. (I had lots of experience installing it without the base previously, so it was no big deal). Only problem was that on the plane the seat belt buckle goes right in front of the baby, and withint 2 minutes my daughter figured out how to unlatch it! Oops!! I tried a seatbelt extender and that didn't help, because the buckle was still in the exact same place. I think that I ended up twisting one side of the seat belt so that the buckle was upside down and she couldn't unlatch it. The seat fit nicely in the airplane seat. Hope this helps!