Dragonflight is a Guild/Alliance event that is triggered in Strongholds with the Wizard in the courtyard. Once the event has been triggered you and your fellow adventurers will have ten minutes to slay all four dragons. This is not an easy task as all four need to die at the same time or relatively close. As soon as one dragon drops there is a one minute timer before the remaining dragons flee. To unlock this achievements all four must be slain, here are the named dragons:
Katatheo the Proud - Stronghold Dragonflight
Oxuno The Treacherous - Stronghold Dragonflight
Chrysos The Vain - Stronghold Dragonflight
Ekdos The Cruel - Stronghold Dragonflight