I am looking for an explanation regarding how AC sets their fares. Consider T+ fare classes which are listed as Booking classes M, U, H, Q, V, W and S. Based on my experience M>U>H>Q>W>S. For any flight, I assume that there will be seats allocated to each fare class when the flight is posted (allowed to be booked). I did a small experiment for a return flight YYC - HKG for February 2013. To see all available seats in economy, I checked out the L fare. All seats in Y are available. Next, I entered the T+ option. The fare posted was $2086. The summary shows that I was assigned the following booking fare classes - U for YYC -VYR, and H for YVR - HKG return. Both fares are at the higher end of T+. I then checked available fare classes for YYC - VYR for the flight without a HKG connection. Lo and behold there were enough S fares to fill the plane. I called AC and asked if I can purchase a S fare for YYC-HKG. After a long wait, I was told that S fare is not available. There was M but no Q, W or S for this empty flight. I called UA and was given fares for each booking class for the date. I hope an AC representative will come on with some explanation on how T+ fares are determined for TPAC flights.