From AAID

The Aircraft Accident Investigation Department shall forward a notification of an accident, a serious incident to be investigated with a minimum of delay and by the most suitable and quickest means available to the State of Registry; the State of the Operator; the State of Design; the State of Manufacture; and the International Civil Aviation Organization, when the aircraft involved is of a maximum mass of over 2250 kg or is a turbojet-powered aeroplane using the form below;