Definitely rearfacing. I would come prepared with your manual and copies of the applicable FAA documents that show that it is allowed by the FAA.
How heavy and tall is your son? Not sure if you're looking for a long-term seat or a travel-only seat, that would make a difference in recommendations. The *easiest* thing to do would be to buy a larger infant seat (SnugRide35, Onboard 35) and learn how to install it baseless. Then you could take your stroller and wheel him as far as the gate, and just carry the bucket onto the plane while gate-checking the stroller.
Another good travel option is the Combi Coccoro. If you plan to continue rearfacing your son after he turns a year (highly recommended, it's 5x safer) it will not be the last car seat you ever have to buy, but it is short-shelled and will make it a lot easier to fit it rearfacing in the plane rows. A more
budget option is a Cosco Scenera, which can be found for about $40. Target carries one that rearfaces to 40lbs, which is the one I would suggest getting -- again, with the goal in mind of keeping your son rearfacing in vehicles to the limits of your seats.
If you would prefer to purchase a follow-up seat for the infant bucket to be used full-time in the car, and also take it on the plane, that recommendation would vary based on your son's height and weight. Without knowing that, I might suggest the Safety 1st Complete Air 65 as it has a tall shell and a 40lb rearfacing weight limit, a 65lb forward facing weight limit, and it can be installed very upright. That will make it easier to squeeze it into the plane's rows.
Also, if your son's seat cannot be accomodated in the seats the airline has you in, I believe they have to move you to another seating position (within the same class) that will accomodate his seats. I can try to find the reference on that if need be, or it may be in the aforementioned circular.
Hope that helps. And
to you for restraining your baby on the plane!
ETA: Note the following passage in the circular --
b. Proper Use of CRS. If a child occupies a CRS, a parent/guardian must accompany the child and the aircraft operator must comply with the requirements that the child is properly secured in the CRS, the CRS is properly secured in a forward-facing seat, the child does not exceed the weight limits of the CRS, and the CRS is approved and has the proper labels or markings.
This indicates that the child restraint (CRS) must be installed on a forward-facing PLANE seat, not that the CRS must be installed forward-facing. A lot of confusion tends to come from this passage, so it's best to be aware of it.
And here's the passage I referenced above:
f. Operators Prohibiting CRS Use. No aircraft operator may prohibit a child from using an approved CRS when the parent/guardian purchases a seat for the child. If an approved CRS, for which a ticket has been purchased, does not fit in a particular seat on the aircraft, the aircraft operator has the responsibility to accommodate the CRS in another seat in the same class of service.
Clause 2 of which reads:
(2) An aft-facing CRS that can not be installed properly, because of minimal pitch (distance between seats) between rows, can be moved to a bulkhead seat or a seat in a row with additional pitch.
