How is it decided which States will participate in an aircraft Accident Investigation?

Article 26 of the Convention on International Civil Aviation (Chicago Convention) states that, in the event of an accident to an aircraft of a Contracting State occurring in another Contracting State, and involving either death, serious injury, or serious technical defect in the aircraft or air navigation facilities, the State in which the accident occurs will institute an inquiry into the circumstances of the accident.

Annex 13 (Aircraft Accident and Incident Investigation) to the Convention provides further international requirements for the investigation of aircraft accidents and incidents. It spells out which States may participate in an investigation, such as the States of Occurrence, Registry, Operator, Design and Manufacture. It also defines the rights and responsibilities of such States.

The State of Occurrence may delegate all or part of the investigation to another State or a regional accident and incident investigation organization, and may call on the best technical expertise available from any source to assist with the investigation. States of Registry, Operator, Design and Manufacture who participate in an investigation are entitled to appoint an accredited representative (with or without associated advisers) to take part in the investigation.

A State which has a special interest in an accident, by virtue of fatalities or serious injuries to its citizens for instance, is entitled to appoint an expert entitled to: visit the scene of the accident; have access to the relevant factual information which is approved for public release by the State conducting the investigation, and information on the progress of the investigation; receive a copy of the accident investigation Final Report. ICAO officials only participate in accident investigations upon special request from the State responsible for conducting the investigation.