In the first phase, the Investigator(s) travel(s) to the scene of the accident. In cooperation with the Cantonal Police of the accident location, they investigate the wreckage and the accident site. Next, all information (such as flight preparation documents, weather reports, radar analyses, etc.) that could help explain the accident is gathered together.
Within 24 to 48 hours, the STSB compiles a report of initial findings in which the accident and the instigation of an investigation are notified. This report only includes significant information about the aircraft, the flight personnel involved, the scene of the accident and the damage that has occurred. It provides a brief account of the sequence of events of the accident, but without any analysis. It is submitted to the parties concerned as well as the Federal Office of Civil Aviation (FOCA).
In the case of accidents involving larger aircraft, flight recorders - also generally referred to as the "black box" - are often available for a reconstruction of the events:
1. The Flight Data Recorder (FDR) is a device which records the flight parameters of the previous approx. 25 flying hours. The oldest FDRs record only six parameters whereas the most modern record up to one thousand.
2. The Cockpit Voice Recorder (CVR) is a voice recording unit which records the environmental noise in the cockpit or cabin for the previous 30 to 120 minutes.
Even in the case of smaller aircraft, recordings are nowadays often available from GPS devices, collision avoidance systems or loggers; these can be used to clarify an accident or a serious incident. In each case, all the available data, such as technical recordings, statements of persons involved and eye witnesses, the inspection of equipment and systems, medical reports, weather reports, etc. can be used to understand and explain an event as well as possible.
The representatives of states involved, the manufacturer of the aircraft, the engines and other equipment, as well as representatives of the airline company, air traffic control and trade unions can take part in the investigation.
Should it prove necessary, the STSB-AV publishes an interim report within a few weeks, with safety-critical information for the attention of the competent supervisory authority. The STSB can issue safety recommendations at any time during the investigation if it considers this necessary in order to improve aviation safety.
On the basis of the initial telephone clarifications, the STSB Investigator decides whether an investigation will be initiated. If necessary, he mobilises additional full- or part-time Investigators and decides whether external specialists or experts must be consulted.
The STSB may waive investigative actions if these would involve disproportionate expense in relation to the expected results.
Interested persons and organizations may request to conduct certain investigative actions. However, the STSB does not have the obligation to to fulfill such requests.
The STSB's investigation is conducted independently of any penal or administrative proceedings. However, the prosecuting authorities, the administrative agencies and the STSB coordinate their activities.
The accident investigation by the STSB includes recording the accident, securing the evidence and analysing the journey data. To these are added interviews with witnesses and respondents, and a study of other investigation filess. If necessary, the Investigator arranges for special investigations. The findings of the investigation are analysed and summarised in the investigation report.
Data which may help the investigation of the incident have to be secured. This includes especially any videography, photography and audio recordings and data of safety devices.
The STSB decides on the release of the accident site, the wreckage and its contents, and the pieces of the wreckage. Orders of the prosecuting authorities remain reserved.