The pilot-in-command of the August 4 Phuket-Delhi Air India flight, which suffered a sudden loss of altitude during cruise and left 24 people injured, tested "non-negative" for a psychoactive substance in a confirmatory test, according to a preliminary report released Friday by the Aircraft Accident Investigation Bureau (AAIB). The Airbus A320neo, carrying 145 people, suffered an "altitude upset" after losing all three of its hydraulic systems within seconds while cruising at 36,000 feet, the agency found.

According to the AAIB's preliminary findings, the flight-control system first detected a loss of pressure in the Green hydraulic system, followed four seconds later by a loss of pressure in both the Blue and Yellow hydraulic systems. The autopilot subsequently disengaged, triggering a cockpit warning, and a stall warning sounded briefly during the sequence. The co-pilot, who was flying the aircraft at the time, initially attempted to manage the situation before the pilot-in-command took over control. During the upset, the aircraft climbed 372 feet above its assigned altitude before dropping 292 feet below it, a dramatic swing that occurred within a matter of seconds.

The Blue hydraulic system was the first to recover, followed shortly afterward by the Yellow and Green systems, restoring functionality to the aircraft's flight-control surfaces. The aircraft stabilised once hydraulic pressure was restored and subsequently landed safely in Delhi. The incident, involving flight AI2379, had initially been reported as a turbulence encounter, but the AAIB's investigation has since determined that the underlying cause was the near-simultaneous loss of hydraulic pressure rather than atmospheric turbulence, with no adverse weather reported at the time. The preliminary report also noted damage to several parts of the aircraft's cabin, including ceiling panels and overhead storage areas, consistent with the severity of the sudden altitude changes experienced during the incident. Of the 145 people on board, 24 received medical assistance after landing, with four sustaining serious injuries.

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Because the flight originated outside India, both pilots underwent mandatory post-flight breathalyser examinations upon arrival in Delhi, the results of which were reported as satisfactory. Both pilots were also screened for psychoactive substances; the co-pilot's sample returned a negative result, while the pilot-in-command's initial sample came back non-negative, prompting a blood sample to be sent to a pathological laboratory for confirmatory testing. That confirmatory test subsequently verified the non-negative result. The AAIB's 10-page report noted that this finding does not establish that the pilot-in-command's drug use contributed to the hydraulic failure or the resulting altitude upset, and said its investigation into the technical and other aspects of the accident remains ongoing.

Nonetheless, the agency characterized the confirmed use of a psychoactive substance as a "serious concern" and issued an urgent interim safety recommendation directing the Directorate General of Civil Aviation (DGCA) to take appropriate action to prevent substance abuse among flight crews. "In view of a non-negative result for psychoactive substances for one of the flight crew, it is recommended that DGCA may take appropriate actions as deemed fit to prevent abuse of psychoactive substances," the AAIB said in its report.

On the technical side, investigators from France's Bureau d'Enquêtes et d'Analyses (BEA) and from Airbus have since inspected the aircraft and retrieved hydraulic components and fluid samples for further laboratory analysis at AAIB headquarters. Both the cockpit voice recorder and flight data recorder have also been recovered and downloaded as part of the broader investigation into the cause of the near-simultaneous hydraulic system failure, with a more detailed final report expected once the technical analysis is complete.

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