Originally Posted by
sdm1130
The AirTrain is not airside, so you need to re-clear security if using it to tranfer between terminals.
There is also a bus that runs airside between A and C. Depending on the time of day, it is usually a much faster option.
Correction: ALWAYS a much faster option. Even if there was no line to re-clear security, you have to keep in mind that the AirTrain is pulled by a team of gerbils, or so its average speed would make it seem.