D1 is a high priority non rev space available (nrsa) pass priority. Employees receive 4 one way D1 passes per year (unless it's changed). All other pass riding for employees is at the D2 priority. D1's are basically vacation passes.... you get 2 roundtrip chances per year at getting on ahead of all the D2's. Used to only get 1 D1 roundtrip per year, but AA gave an extra a few years back.

They certainly are not confirmed passes...simply higher priority standby than the usual D2...or even worse D3 (buddy pass) priority.

While I've certainly been "disappointed" in not getting on the flights I wanted to standby on in my past airline career, I do not understand why anyone flying standby would get hacked off about not getting on a flight unless they buy a ticket for it. But that's just me...and I'm unusually tame when it comes to this flying game.