In response to the Recommendation, ICAO developed the training guidelines contained in this circular. The circular discusses the experience and employment background required for training as an aircraft accident investigator. It also outlines the progressive training that is considered necessary to qualify a person for the various investigation roles, including appointment as the investigator-in-charge of an investigation into a major accident involving a large transport category aircraft. ICAO acknowledges that training guidelines are evolutionary in nature and may need to be updated periodically.