I have firsthand experience with a related issue from a couple of weeks ago. If you made use of the extra baggage benefit conferred by *G, and your non-status Aeroplan membership/fare doesn't cover the extra bag you checked, the gate agent will not be able to print you a new boarding pass with "Aeroplan" in the FFP field, simply because you now owe the airline baggage fees after taking off your *G.

On another trip, I decided to use my old boarding pass after changing my FFP number to see how they'd handle the unpaid baggage charge (cheeky experimentation on my part), and the boarding pass wouldn't let me on the plane. Had to handle everything with the flustered gate agent trying to send the plane off.

On two other occasions (another trip with a connection), I had managed to sneak past the unpaid baggage charge and board my flight while crediting to my preferred non-*G program, though, but I'm not sure if it's ethical to share it aloud nor have I had the opportunity/care to reproduce it.

And just to nitpick the prior conversation a bit, but I'd love to be corrected if I'm wrong, you CAN have two FFPs in the FQTV field. From the above experience, I was swapping between my *G and non-*G account the evening before my flight by calling Reservations, and this is what I noticed.

The telephone agent inputted my desired FFP, and it showed up in the following places:

• on your boarding pass, paper or digital
• on aircanada.com under passenger details
• at the check-in kiosk

Those factors led me to believe that I'd successfully changed to my lone, desired FFP

However, TWO FFPs showed up on:

• the Cowtool PNR viewer
• at the MLL agent's computer

In the latter case, she was freaked out that there was two and promptly asked which one I'd like removed, which also put me on the spot because I certainly hadn't expected to have two in the field, either.

I had no idea what would have happened if I flew with two FFPs attached, mainly because I had the baggage issue described above to sort out