Well that photo shows a C-17 not a C-141, and it's not inflight.
C-17 has 27 seats on each sidewall that fold up against the side when not in use. An additional 54 seats can be installed down the center (as in the photo), these seats are stowed on top of the rear cargo door when not in use and travel with the aircraft. So 108 pax using assets available on the aircraft.
C-17 bases used to have, and may still, palletized airline style seats originally used on the C-141. If used these would be installed down the center of the cargo bay. 6 seats to a pallet x 12 pallet positions = 72 seats. These would normally be used for VIPs.
Also depending on the mission and number of pax a palletized galley/lav combo may be installed. It would be right under the bottom of the photo.
Edit: Also number of available seats is not necessarily the limiting factor for pax. Failure to have adequate urinal/toilet facilities can make a long flight nasty. Chart used to determine # lavs required is called, I shit you not, the "P" chart.
[Edited 2004-12-27 16:52:59]
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