Most think that the Gray Angels are just flamboyant pirates that conduct train robberies and hijack skyships. In reality, they are an organized crime syndicate that controls the black market of extraplanar magitech. They are rumored to be based out of ar-Idas or the pirate island of Zabar since the pirates always fly south after a raid. That's just an unsubstantiated rumor, since their base of operations has never been located.
The Gray Angels are known for their tactic of silently descending out of the sky onto their victims. Small bands of pirates riding flying mounts, or flying under their own power. They sneak onto skyships in the middle of the night, throw crew and passengers overboard, and hijack them. They use hijacked skyships to ambush trains out in the wilderness, loading valuables onto stolen vehicles.
The booty makes its way to thief's guilds where the items can be fenced and the skyships can be re-painted for sale in other lands.
The main characteristic of Gray Angels is their ability to fly, preferably under their own power. Smaller folk on flying animals, goblins on giant bats or renegade Crow Riders form a significant portion of their membership. Aarackockra, other flying mortals, and pirates with flying devices make up the balance of the membership.
Flying south after an attack is a distraction. The Gray Angels maintain dozens of safehouses throughout Western Krosia, they don't actually have a main headquarters. They prefer to operate as a widespread network of associated brigands.