My great-grandfather died in an accident. Should I perform Chaturthi Shradh for him?

If your great-grandfather passed away on a Chaturthi Tithi, then yes — Chaturthi Shradh is the prescribed day. Additionally, even if the tithi was different, certain regional śāstra traditions prescribe Chaturthi Shradh for ancestors who died in accidents or sudden circumstances, as their souls may require sustained attention. Consulting a learned pandit will clarify the appropriate approach for your family’s specific situation.