Originally Posted by
ludocdoc
If the A line is beastly, I've sometimes contemplated l walking out and re-clearing security at one of the conventional A Terminal checkpoints or at one of the others. The other airside shuttle is from C to F, so the options would be to re-enter at C or hike all they way to F landside. As a former philly native, I'm sorry to say I forget if this landside hike can be done indoors.
It is not possible to walk from the International Arrivals Hall to F indoors (you can get from B to C and from D to F indoors landside, but getting from A to B requires walking along the sidewalk, I think, and getting from C to D requires either the sidewalk or the (covered) train platform).
The OP's parents are probably best off reclearing at A and then taking the shuttle from A to F. If the line after baggage check for connections is long, they can always try the ordinary checkpoints at A-West or A-East, which are rarely very crowded in my experience.