A month after the deadly Air India flight crash in Ahmedabad, where 241 of the 242 people onboard flight AI 171 died, the Aircraft Accident Investigation Bureau (AAIB) released a preliminary report on Friday night (July 11).

The 15-page report stated that the two engine fuel control switches onboard transitioned from ‘RUN’ to ‘CUTOFF’ position within a second of each other, moments after lift-off. One of the two pilots is recorded as asking the other why he cut off the fuel, to which the other pilot responded, saying he did not.

According to a Reuters report, pilots usually cannot accidentally move the switches, but if switched off, they can immediately cut off engine power. The report has led to further questions about the switches’ functioning and what exactly happened, and demands for greater scrutiny of the cockpit voice recorder (CVR). It is one of the two black boxes on aircraft, alongside the Flight Data Recorder (FDR).

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As The Indian Express reported, most preliminary air accident investigation reports in the past have been a compilation of basic facts, but this report provides more details of what led to the crash. However, it includes limited information on the most crucial exchange that took place in the cockpit between pilots. What usually happens in such investigations, and what is the AAIB?

Who conducts aircraft crash investigations?

Matters of international civil aviation are today governed by the Convention on International Civil Aviation, or the Chicago Convention, signed in 1944. The International Civil Aviation Organization (ICAO), a UN agency with 193 member countries (including India, the United States, and the United Kingdom), oversees its technical standards.

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Annex 13 of this convention lays out the international protocols for investigating aircraft accidents and serious incidents. It bestows the responsibility for investigation with the ‘State of Occurrence’ — the country where the accident happened.

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In addition, other countries connected to the aircraft have a formal right to participate. These include the ‘State of Registry’ (where the aircraft is registered), the ‘State of the Operator’ (which operated the flight), the ‘State of Design’, and the ‘State of Manufacture’ (of the aircraft in question).

And what is the Aircraft Accident Investigation Bureau (AAIB)?

Since the AI 171 air crash occurred on Indian soil, India holds the State of Occurrence right. The investigation into the accident is thus led by the Aircraft Accident Investigation Bureau (AAIB), the government agency under India’s Ministry of Civil Aviation that is responsible for investigating civil aviation accidents and serious incidents.

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The government can make rules for investigations under Section 7 of the Aircraft Act of 1934. Until 2012, the Air Safety Directorate of the Directorate General of Civil Aviation (under the aviation ministry) investigated accidents and safety-related incidents.

“In accordance with Standards and Recommended Practices (SARPs) issued by the International Civil Aviation Organization (ICAO) and to provide independence of investigation function from the regulatory function, the Government of India decided to establish a Bureau independent of the DGCA,” the official website states.

What are the AAIB’s functions?

In general, the AAIB classifies ‘Safety Occurrences’ involving aircraft operating in the Indian airspace into the categories of Accidents, Serious Incidents and Incidents. It investigates all Accidents and Serious Incidents involving aircraft with All Up Weight (the total weight of an aircraft with passengers and cargo) of more than 2,250 kg, as well as Turbojet aircraft. It can also investigate other cases if necessary.

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Under Rule 3 of Aircraft (Investigation of Accidents and Incidents) Rules, 2017, the sole objective of the investigations carried out by AAIB is the prevention of accidents and incidents and not to apportion blame or liability.

As part of the investigation, AAIB deputes one or more Investigators to reach the site and gather evidence soon after it receives notice of the incident. Its website states that the primary aim of the initial investigation is to gather and preserve perishable evidence for subsequent analysis. This can include obtaining samples of the wreckage and from the surroundings, retrieving the black boxes, and so on.

More from Express | The fuel control switches that are now at the heart of the AI 171 crash probe

The Investigation team reviews all evidence collected to assess the detailed examinations that must be conducted. Domain experts can then be called in. AAIB also has a Memorandum of Understanding with agencies such as Hindustan Aeronautics Limited and the DGCA for using their laboratories.

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Further, documents and records gathered from the Operator, Regulator, involved Personnel, or other stakeholders are studied and analysed. The AAIB is also mandated immediate and unrestricted access to all relevant evidence from any agency/organisation without seeking prior consent from judicial bodies or other government authorities.

After completion of the investigation, a draft report is presented internally and accepted by the AAIB Director General. Following further consultations and reviews, the final report is made public and published on the official website. The accepted ‘Final Investigation Reports’ are also forwarded to the ICAO and the states participating in the investigation.

The AAIB also conducts safety studies from time to time. The recommendations made in the Investigation Reports and Safety Studies are forwarded to the DGCA, India, or Civil Aviation Regulatory bodies of other ICAO Contracting States for their implementation and follow-up.