Oh really? Last time I looked Annex 13:
5.1 The State of Occurrence shall institute an investigation into the circumstances of the accident and be responsible for the conduct of the investigation, but it may delegate the whole or any part of the conducting of such investigation to another State by mutual arrangement and consent. In any event the State of Occurrence shall use every means to facilitate the investigation.
For Sure, State of Registry and manufacturer have a right to be involved but the are not automatically liable to
initiate an investigation when an accident occurs in a contracting state; that responsibility lies with the State of Occurrence, Mr vapilot2004.