If an accident or serious incident involving one or more aircraft takes place, it is to be reported to the AAIB via the alarm control centre of REGA (Tel. 1414). The definitions which determine whether an event is an "accident" or a "serious incident" are given in the Swiss Aviation Manual (AIP ENR 1.14), and on this website under definitions. Next, an Investigator is appointed according to the AAIB duty roster. Depending on the event, this person can also employ the support of further Investigators or, if necessary, external experts.
If an event takes place abroad which concerns Switzerland, the AAIB can appoint a representative on the basis of the provisions of Appendix 13, to the Convention on International Civil Aviation who will monitor the progress of the investigation and provide support if necessary.