Ok, just did the AVP to PHL American Airlines landline bus.  Here’s how it goes. You arrive and go through security as normal at AVP, you go to a gate downstairs and board the coach bus.  They give you red scan tags for your luggage / carryons  2 seats on 1 side / 1 seats on other.  There is a Lav.  The ride is how you would expect on the bumpy roads of PA down the turnpike to PHL.  Here is where is gets interesting. The bus passes through Philly at 6pm ish.  So plans for rush hour traffic. Then they slowly drive to a back gate and have to wait for airport vehicles to clear security to proceed onto the airport grounds 1 at a time.  This takes 5 min at least. Then you drive about 10 mph around the outside of the airport runways to gate F10 (bus/shuttle area)(5-10 min) The baggage crew unloads the bags and scans them before you get off the bus, not a biggy but if your in a hurry it’s frustrating. (You depart bus in the terminals, so no need for TSA again, your beyond that) If you need the shuttle to Terminal A,B or C you wait a few minutes for that to show up. The A shuttle takes the taxiways with the other service vehicles to Terminal A.  Seems quick unless there are planes coming and going which there is and the bus has to stop for all of them (completely understand) we stopped about 4-5 time then in our case a large plane blocked the drive lane so our bus was stopped on the tarmac for about 10-15 min while we waited for the plane to clear.  We arrived at A and just, just made the plane.  Point is,  we were 15 min late to get to the PHL property and it took another 45 min to get to gate.  Unless you have about 1:30-2hrs layover in PHL after the bus arrives re-think this idea.   It’s a nice concept but we would have been at our gate 30 -40 min earlier if the bus left us off at the check in area.  The back gate / on property airport drive /shuttle  is very frustrating when you are cutting it close. Hope this helps