Didn't find an answer when I searched this forum but I'm curious so I'll put it out there to the gurus.

I realize that being waitlisted is based on the surface on availability...but what else is it based on?

I usually upgrade at the minute I can, so last night YVR-YYZ, lots of space, no issues got it right away. This morning I had my alarm set to upgrade YYZ-MIA...I didn't figure in the time difference!!! So I was late by 2 hours. Waiiitttt Listtttttt . But checking the seat map I noticed 5 of 8 J seats are still open and I thought they'd at least auto upgrade to 50% of capacity no?

I've only ever failed one other time when jumping on the opening window of upgrade which was last week YVR-YEG I immediately got waitlisted, then at the gate got it anyway, so fingers are crossed for MIA (since it isn't charging me any extra credits) but I'm wondering if there's a magic algorithm or certain routes, or any light to be shed on when you get waitlisted.

As you said, it's all about availability - but for an instant upgrade, the availability is for 'R' class, not the number of J seats still available. The number of R "fares" made available can therefore be adjusted by the AC revenue management folk; if they expect that J will sell out on any particular flight, they may not make any R available at all.

Case in point, I'm flying HKG-YYZ on Monday, and the J cabin was wide open; J9 and the seat map looked like there were over 30 seats still open... But there was no R availability so I went onto the waitlist.

The upgrade can then clear at any point, in advance or just at the airport... But it's under AC's control - it all comes down to revenue management.

You can see the R availability in most of the online tools (expertflyer is my preferred tool) and if a flight shows R>0 then an upgrade request will clear right away.

Thanks, that's helpful, I had the expertflyer membership for a bit but wasn't really using it so I scrapped it. I figured it was something like this but I wondered if there might be an actual formula someone knew. It's funny though in the times I have been waitlisted I've never been upgraded via email, I've heard of it happening but mine have always been at the gate.

http://www.flyertalk.com/forum/air-c...-priority.html

Experflyer, kvs or flightstats will tell you how many J seats are left; not the seat map. Seat map means nothing ever.

Many people buy tickets and don't select a seat; a map that shows 5 open seats could have 5,4,3,2,1,0 seats actually left.