A preliminary report on the devastating Air India crash last month has found that both fuel control switches were in the cut-off position – a step that turns of the engines – just moments before the plane crashed in Ahmedabad, India. Audio from the cockpit detailed in the report suggests confusion between the two pilots.

One pilot is heard asking his colleague why he "did the cut-off", to which the other replied that he did not do so. It remains unclear who asked the question and who answered. However, the Airline Pilots' Association of India (ALPA India) has reacted to the preliminary report on the crash, raising concerns over the way the investigation is being handled. In a statement reported by Indian media, the pilots' union said it was "surprised at the secrecy surrounding these investigations" and alleged that "suitably qualified personnel were not taken on board for the probe".

ALPA India's president, Captain Sam Thomas, continued in the statement: "We feel that the investigation is being driven in a direction presuming the guilt of pilots and we strongly object to this line of thought.

The union has urged the authorities to allow it to join the process to help ensure transparency.

“We once again request the powers that be to include us even in the capacity of observers so as to provide the requisite transparency in the investigations,” the statement added.

The Aircraft Accident Investigation Bureau (AAIB), which is leading the investigation into the June 12 crash and is supported by UK and US safety agencies, filed the preliminary report, which is based on the initial findings of the investigation, with Indian authorities on Friday. Both of the plane's black boxes, which capture cockpit audio and flight data, were recovered in the days following the tragedy, providing vital information for investigators.

One engine was in the process of regaining thrust when the aircraft crashed. The other was relit but had yet to gain thrust. The report does not offer any conclusions as to how the switches were moved.

Flight AI171 reached only around 625 feet before slamming into a densely populated residential area. Five buildings were destroyed in the crash, according to the report. A British national, Vishwash Kumar Ramesh, was the only person among those onboard the Boeing Dreamliner who survived and remarkably managed to walk away from the wreckage despite his injuries.

The captain, Sumeet Sabharwal, and first officer Clive Kundar were highly experienced with wide-bodied aircraft, clocking up more than 9,000 hours of combined flying experience, according the Directorate General of Civil Aviation (DGCA).

The AAIB said the probe is ongoing, with a final report to be submitted at a later date.