After an injury during the course of a flight occurs, the injured passenger should immediately seek the advice of an experienced aviation attorney to determine not only if he or she has a case, but what laws will apply to the action. Among the first question the attorney will ask is whether the passenger was injured aboard a domestic or international flight.
A domestic flight is one which begins and ends within the same country. The passenger will usually not have to clear immigration and customs and does need a passport to travel. In the event of an injury aboard a domestic flight, the laws of the United States(or country where it occurred) will govern the outcome of the case. Those laws will determine whether the passenger can bring certain claims, or whether those claims or barred by operation of law. There may be differences in statutes of limitations, which limit the time that one has to bring a claim and certain other written notice requirements that make it mandatory for a passenger to seek counsel immediately.
There are also laws known as statutes of repose that protect aircraft manufacturers from claims brought as against older aircraft unless those aircraft are used in commercial aviation, and laws that "pre-empt" or restrict state law claims where the FAA or other federal authority has handed down certain rules or guidelines.
Although these rules are by no means absolute, the majority of accidents aboard general aviation aircraft occur during domestic flights whereas international flights are typicall run by commercial aviation carriers.
Internaional flights are typicall operated by commercial aviation carriers and are "longer haul" flights. Injuries that occur during the course of an international flight are governed exclusively by the Montreal Convention.
Read more about the Montreal Convention here.