E.C.
what age and size is your child? The Cosco scenera *is* pretty well regarded as an affordable and safe option whose light weight makes it travel-friendly - see this carseatblog.com entry from a certified child passenger safety tech: http://carseatblog.com/2813/dorel-cosco-scenera-review-a-...
the same tech also has some YouTube installation videos featuring the Scenera that might be helpful
Rear-facing with seatbelt: http://www.youtube.com/user/CarSeatSite#p/u/13/1QVlTKBIb70
Rear-facing with LATCH:
http://www.youtube.com/user/CarSeatSite#p/u/14/V5HnuYzFtWM
Forward facing with seat belt:
http://www.youtube.com/user/CarSeatSite#p/u/8/orwlrrlRI8A
Forward facing with LATCH:
http://www.youtube.com/user/CarSeatSite#p/u/9/12nBiM0mudU
Also, the following carseatblog entries have some helpful tips for air travel with children:
http://carseatblog.com/6599/airplanes-carseats-and-kids—w...
http://carseatblog.com/6635/airplanes-carseats-and-kids—w...
hope that helps!