From Guild Wars Wiki
Possible locations in Mineral Springs.
 Items dropped
- Hyl Thunderwing has six possible spawn points in Mineral Springs, which he shares with five other Avicara bosses: Ryk Arrowwing, Myd Springclaw, Nhy Darkclaw, Syr Honorcrest, and Wyt Sharpfeather. This doesn't apply while the quest Defend Droknar's Forge is active. Instead, he and all the Avicara bosses have a fixed location.