• How does the upgrade waitlist work?

500-Mile electronic / sticker upgrades may clear at any time between the opening of the relevant upgrade window (based on status) and the time the gate agent closes the aircraft door. Note that upgrades only clear when appropriate inventory is made available and elites do not necessarily clear at their upgrade window. Thus, passengers will often find themselves at the gate looking at the upgrade waitlist on the monitor. In the case of a connecting itinerary, the upgrade windows for the entire itinerary are based on the departure time of the originating flight, rather than each individual flight, so upgrades for connecting flights may clear prior to the opening of the upgrade window for that particular flight. If upgrades are not cleared prior to check-in by the automated upgrade system, passengers must request to be added to the airport upgrade waitlist at check-in, and must have sufficient 500-mile electronic upgrades in their account for the flight in question to be added to the airport list (see: How many 500-mile electronic upgrades / stickers do I need and when must I have them?).

Upgrade priority is based on:
Note that check-in time no longer affects upgrade priority, although it does still impact standby priority.

Elites requesting a companion upgrade will have their status applied to both passengers, but will, by default, only clear if both upgrades become available simultaneously, and may be passed over if only one upgrade inventory slot becomes available. This ‘no-split’ designation can be removed manually by calling AA Reservations, however, this also removes the linking of the elite member’s status to the companion. Note that this companion linking apparently does not always transfer properly from the automated upgrade system to the airport upgrade waitlist.

Award and systemwide upgrades come from distinct inventory compared to 500-mile electronic upgrades, and may clear at any time between the original request and the time when the gate agent closes the aircraft door. As of August 2013, award and systemwide upgrade requests are automatically transferred to the airport waitlist and priority is based on the list above, with no impact of check-in time. There is no set priority amongst the different upgrade instruments, although some foreign stations have been reported to favor Award Upgrades over systemwide upgrades and domestic gate agents may favor 500-mile electronic upgrades over award and systemwide upgrades for expediency since the former does not require reticketing.

Wiki: Upgrade: Waitlists | PALL List | Inventory Classes
AA.com: 500-mile Electronic and EXP upgrades | EXP Upgrade Info | PLT Upgrade Info | GLD Upgrade Info
FT: 500-Mile electronic upgrade / sticker protocols (2009, consolidated)
FT: Companion upgrades - linking and splitting of elite status and PNRs (consolidated)
FT: Connecting passengers trump originating passengers on upgrade waitlist
FT: Impact of Y & B Fares on EXP and 500-mile electronic / sticker upgrade priority
FT: Upgrade waitlist info only available at airport, not by phone or web
FT: Can I upgrade from standby? (consolidated)