Conduct of an Investigation
When the decision to remove a part or take a sample is taken, the greatest precautions must be used to ensure that evidence essential to the investigation is not altered.
Following this, on-site observation (moving flight surfaces or flight controls, initial examination of the engines) is completed by a detailed examination of the cockpit, warning displays, switch and control positions.
Investigators work in concert with the representatives of the judicicial authorities. They can also request autopsies or use autopsy reports.
Finally, investigators also gather together all the factual evidence linked to the event such as witness testimony, flight crew and aircraft files and logs, flight preparation data, meteorological conditions, as well as evidence linked to air traffic control (radio communication transcripts, radar tracks). In the context of general aviation, collecting evidence is often relatively fast, though continuing the investigation can pose problems (few witnesses, aircraft rarely equipped with recorders, operations in non-controlled airspace, few or no radar tracks or communication recordings, flight preparation documents destroyed or not stored).
The three phases of an investigation
Phase 1: identification, preservation, information gathering
This is an essential phase in a technical investigation, as the information gathered at this level forms the basis for the follow-up work. This is when the flight recorders(CVR/FDR), if installed, are removed.
Phase 2: Examinations and research
This phase involves detailed examination of the parts recovered.
The readout of flight recorders provides a technical interpretation of the moments leading up to the event. Based the initial interpretation, the phase of detailed examination, tests and the search for specific details (engines, flight controls, flight instruments, etc.) completes the first overview of the facts.
The investigator-in-charge studies the results of the examinations and the information collected in phase 1 with the investigation team. On the basis of these results, simulations can be set up in order to validate some flight sequences. A study of these elements can lead back to phase 1 with a view to completing the initial information gathered.
Phase 3: Analysis and conclusions
Following this phase of gathering and consolidating factual information, which is often relatively long, the investigator-in-charge brings together all of the evidence and documentation from this work in order to analyze the circumstances of the accident and build the most precise scenario by identifying the safety failings. He specifically tries to study the origins of and the contributing factors to the event by taking into account all aspects linked to psychology, communication, ergonomics, behaviour, decision-making, etc. These aspects of the investigation are grouped under the “human factors” heading.
In the context of general aviation, this phase is often made difficult by the lack of evidence collected and by non-validated information that makes it impossible to determine the accident scenario