LOL, most car seat I see for sale in SG, are not flight certified. I've only seen 1 or 2 models for sale in SG, that are flight certified. In fact, I went down to like OG, and asked about FAA approved car seats, the salesperson said no, then I checked all for sale and nothing was FAA approved. Went down to some baby warehouse sale thing, and only 1 model has the flight certified logo and I think it was their most expensive model.
Other things to consider for bringing car seat onto plane, is the space, especially if you are taking economy. First is the lateral space, most car seats are quite wide. The adult sitting beside might have lesser shoulder space. Second is the seat pitch, if you did not get a bulkhead row, the person in front reclines, it is already quite near for us adults, it would be even lesser space for a child with a car seat. Lastly, will be your transport upon arrival, will it be convenient or are you taking public transport and the carrying of the car seat during transit, if any?
I've not flown with a car seat, so these are all just pointers I can think of, not the actual experience.
Not much help I guess, if the seat belts are tightened well and doing their job.