I was sure this was a FAQ but couldn't find it (FT didn't seem to like most of my search terms?)

Is it against the rules/unethical to not use the last segment of a round trip ticket? I'm trying to do YYZ-NAS.. return trip is $350+tax, one way is $1100. Booking another one way for NAS-YYZ on another airline is ~$500 (connecting in the US). I'd rather do the direct both ways but AC doesn't have a scheduled flight on my return date.

I tried booking the first segment on AC and return on another airline, but all the online sites seem to use the one-way price which makes the entire itin $1500+

Any suggestions?

I think the title of your thread anwsers your question. Although it's been quite awhile since I've had to do it, I've never heard of it being a problem... especially if you are using two different airlines.

But just don't try to send the unused coupon in to AC to get a refund on any taxes or fees...

It does edge on the ethical, but if you cannot get the return date you want, c'est la vie. Nobody can force you to use the return flight/coupon.

Another suggestion, though, just in case you might have a long weekend later in the winter. Why not book the AC return later in the winter, and the return of the US ticket a few days before that. This would let you have a couple of extra days in the sun later this winter for no additional money beyond your hotel. You'll get miles on both carriers for the full ticket. And no pangs of conscience.

While we are talking about 'throwing away' flight segments, does anybody have experiences to share that involve not showing up for a segment (not the last), walking that segment and then continuing?

I tried this once. Had a non refundable non changable YUL-FRA-YUL ticket on AC and needed to change the departure date, which wasn't possible. Found a really cheap new ticket to FRA on AF. However, I wasn't able to get a reasonably soon return date for the AF ticket. So, since I stayed very close to the airport, I thought I'd give it a try to use the return segment of my AC ticket. I removed the first coupon from my ticket, put on my best tourist attire and approached the check-in agent with a straight face, pretending that I had no clue what was happening when the system complained about the YUL-FRA no show. Fortunately I didn't have to lie, since she didn't ask a single specific question - so I was able to get on the flight no problem. But I was very nervous at the check-in!

Me thinks I was very lucky. But is it unethical? Should I feel guilty? Thoughts?

Yes, you're VERY lucky. It's a bit easier to get away with it if you're using paper ticket; however if you're using ET, then they can clearly see that you didn't use your first coupon/out of sequence.

Whether it is a paper or electronic ticket, if one flight segment is not flown, should not the file with the remaining part of the itinerary be automatically and irrevocably cancelled?

Keep in mind that the actual PNR and ticket are two seperate things. As long as you have a paper ticket, they could build a new PNR & accept the ticket coupon (Of course if the paper ticket is showing as a restricted ticket and different date, you can be sure they will look into it). Same with an E ticket; they just need to build a new PNR, associated the ET with the PNR and you're good to go.

If the flight is completely sold out (or at least if the booking code/fare class is completely sold out?), then they can not build a new PNR for that flight, even if the ticket is showing that flight?

If the flight is completely sold out, AC (or any other airline) can't build a PNR without yield management's help. It's quite rare that someone would have a ticket for a specific flight/date and no reservation these days as they most likely made changes to it causing that to happen or someone screwed up. In that case, they will likely look into it and if they determine that all is legitimate and the pax should have been on the flight, then they could certainly fix it up as long as pax has valid ticket (paper or ET). Even if a flight is near full and original booked class is gone, they can definitely rebook in a higher class to get the pax on since he/she was supposed to be booked on that flight, they'll get a class mismatch prompt if it's an ET but no big deal, they can override it.

Thanks for the replys everyone. I doubt I'd get another chance to go, but even if I did, wouldn't this be back-to-back ticketing? Although since it's on different airlines, no one's the wiser?

My view of the ethics of such things is that it is worst to be a conscious NoShow [twice over] than to be a cost-conscious consumer who intends to fly all four segments. This is just a frugal way of providing yourself with two winter vacations for the price of one, something any righteous Canadian can well defend, particularly when there is little hope of NHL hockey and playoffs to fill up the spring. You are entering into a contract to fly two specifc return trips with two separate airlines, and you are completing your part of the contract with each. By doing what you originally proposed, you are breaking a contract with both airlines.

I managed to get out of a mid-routing segment once on AA by playing the confused young student card (it helps that I'm 25 but look about 19). I was flying SEA-ORD-MKE-STL-SEA, and it was much more convenient for me to get off the plane in ORD and meet my MKE-based friend there, as we were driving south to Louisville for the Kentucky Derby. Not to mention there was a 4hr layover in ORD before the flight for MKE left, so I was saving myself 4 hours of layover, plus flight time, plus the 1.5hr drive from MKE back down to ORD. When I priced out SEA-MKE-SEA, it ended up being $125US more than the via ORD routing, so I took my chances on the segment skipping.

Got to ORD, got off the plane, went to the ticket counter, made big nice doe eyes, and said "I will not be using the last segment of this ticket, as someone has come to pick me up here to save time. You may release my seat to another passenger." The ticket agent said, "You're not really supposed to do that, but it's OK. Don't do it anymore." I replied with a Yes, Sir! and went on my merry way.

As a side note, on the flight back the MKE-STL flight went mechanical, meaning I was going to miss my cnxn in STL and reach SEA late, thus missing the bus home to YVR. I explained all this to the AA gate agent, and she instantly had me put on a Midwest Express flight to Vegas (comfy biz class seats, good cookies!), and an AS flight from Vegas to SEA. I was VERY impressed by their ability to accomodate me with no fuss and no muss, on the most convenient airlines possible.

I've not done it often, but I've never had any grief when I've called to cancel a final segment -- usually for the legitimate reason of not needing to take the last segment because I had to change planes.