<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by smilee:
Scenario 1
(A)YVR-SEA-SFO
(B) SFO-SEA-YYJ
(B) YYJ-SEA-SFO
(A) SFO-YVR
</font>
This would be ticket A with ticket B nested, a valid use of both tickets.
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Scenario 2
(A) YYJ-SFO
(B) SFO-SEA-YYJ
(B) YYJ-SEA-SFO
(A) SFO-YVR
</font>
This would an open-jaw ticket A (YYJ-SFO-YVR) with ticket B (which returns to the point of origin) nested inside. If the usage of ticket B circumvents the minimum stay requirements of ticket A, then it is considered a back-to-back and would violate the carrier's contract of carriage. Transit cities do not matter.
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Scenario 3
(A) CLM – SEA-SFO
(B) SFO-SEA-YYJ
(B) YYJ-SEA-SFO
(A) SFO-SEA-CLM
This is ticket A with ticket B nested inside. This nesting is valid because ticket B does not return to the point of origin.
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">1) My understanding is that they are nested if the two turn around cities are far enough apart. How far is far enough apart?</font>
They are nested if you use ticket B within ticket A. They are back-to-back if they return to the point of origin and circumvent minimum stay requirements. Two cities are considered the same point if they are co-terminals (which YVR and YYJ are not, YYJ and CLM are not, but YVR and YXX may be, SFO and OAK may be - depending on the airline/fare).
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">2) How is a lay person supposed to know as I almost did this a couple of years ago before I heard about flyertalk in a legitimate run (had to escort grandma to SFO, get back to YYJ and then get back to SFO to take her back to YVR?</font>
You would have been expected to buy either one ticket with all segments in one reservation (therefore, if turnaround in SFO was minimal, you would have been forced upon a higher fare).
Alternatively, you could have also been expected to purchase/use your tickets in sequential order. (i.e. YYJ-SFO-YYJ on ticket A with minimal turnaround) and the YYJ-SFO-YVR with minimal turnaound).
In both cases, a higher fare would almost certainly be the outcome.
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">3) I was told back to back is fine if I used two different carriers (in this case AC & AS for example) What about if I used NW and AS??
Not a problem. If you purchase tickets on two different carriers, you should not be violating either carrier's contract of carriage. I don't think whether they are partners matters.