Normally, victims injured or killed on an international flight are protected by the Warsaw Convention. Any actions brought against an airline are governed by this 1929 treaty signed by most of the world's nations. The problem with the Singapore Airlines flight is that it was taking off from a country that had not signed the Warsaw Convention, Taiwan. However, the Convention does cover passengers whose itinerary starts and ends in country that has signed the treaty. This would mean that a passenger traveling on a round trip ticket from the United States would be protected under the Convention.
International flights present many complications.
Passengers and their families need to contact an attorney experienced in this type of complex litigation to learn their legal rights. Also, there may be other non-airline entities which are legally responsible for the crash. Claims against such entities may readies additional complex issues of jurisdiction and proof.