Air India’s Phuket-Delhi flight briefly lost pressure in all three hydraulic systems while cruising at 36,000 feet.
The pilot-in-command tested non-negative for a psychoactive substance in both screening and confirmatory testing.
The altitude upset injured 20 passengers and four cabin crew, while AAIB’s detailed investigation remains underway.
The Aircraft Accident Investigation Bureau (AAIB) has found that the pilot-in-command of an Air India flight from Phuket to Delhi tested “non-negative” for a psychoactive substance in a confirmatory test, while the aircraft briefly lost pressure in all three hydraulic systems during the flight.
The findings were part of AAIB’s preliminary report released on Friday into the August 4 incident involving flight AI 2379, which was later classified as an accident after 24 people were injured.
The Airbus A320 was cruising at Flight Level 360 when its flight-control system first detected a loss of pressure in the green hydraulic system. Within seconds, the blue and yellow systems also lost pressure.
The autopilot disengaged and a continuous repetitive chime sounded, followed by a stall warning that lasted for two seconds. The aircraft initially climbed 372 feet before descending 292 feet from its assigned flight level of 36,000 feet.
The hydraulic systems were subsequently restored, allowing the flight-control surfaces to return to normal and the aircraft to stabilise.
The co-pilot, who was flying the aircraft when the incident occurred, initially responded to the situation before the pilot-in-command took over the controls.
Pilot Tested Non-negative
Both flight crew members underwent post-flight Breath Analyser examinations after the aircraft landed in Delhi. The results were satisfactory, according to the report.
They were subsequently subjected to psychoactive substance detection tests. The pilot-in-command’s sample was found to be non-negative, while the co-pilot’s sample was negative.
Blood samples from both crew members were then sent to a pathological laboratory for confirmatory testing. The pilot-in-command’s confirmatory result was again found to be non-negative, while the co-pilot’s sample remained negative.
“The confirmation of use of psycho-active substance is a serious concern and AAIB recommends appropriate actions by DGCA on priority,” the report said.
AAIB recommended that the Directorate General of Civil Aviation (DGCA) take appropriate action to prevent the abuse of psychoactive substances among flight personnel.
The report, however, does not establish that the pilot’s test result had any role in the hydraulic failure or the aircraft’s altitude upset.
24 People Injured
The flight was carrying 145 people, including 137 passengers, three infants, six cabin crew members and two flight crew members.
During the altitude upset, passengers and cabin crew were thrown around as the seat-belt signs were off. Twenty passengers and four cabin crew members received medical treatment after the aircraft landed in Delhi.
Twenty people were discharged after treatment for minor injuries, while four with serious injuries were hospitalised.
The aircraft also sustained damage inside the cabin, including to overhead stowage bins and ceiling panels. An emergency-exit handle and handrails were broken, a lavatory fixture was uprooted and parts of crew seats were damaged.
The incident was initially reported as turbulence. Based on the injuries sustained and evidence gathered, AAIB later classified it as an accident.
Investigation Into Hydraulic Failure Continues
Maintenance personnel had carried out a pre-flight inspection at Phuket International Airport and recorded no discrepancies apart from an existing Minimum Equipment List (MEL) entry. The flight crew also conducted a walk-around inspection before departure and reported no issues.
The aircraft was operating under an existing MEL item relating to its Power Transfer Unit (PTU), which had been invoked on July 28, 2026.
Despite the incident, the crew continued towards Delhi rather than diverting to the nearest en-route airport. They later contacted Delhi Air Traffic Control and requested medical priority. The aircraft landed safely at Indira Gandhi International Airport at 11 am and reached its parking bay at 11:07 am.
AAIB has recovered the cockpit voice recorder and digital flight data recorder, with the recorded data downloaded for analysis. Investigators have also collected hydraulic components and fluid samples for testing.
Technical experts from France’s Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA) and Airbus inspected the aircraft between August 13 and 15.
The investigation team has also collected maintenance and operational records, fuel and oil samples and information from air traffic control authorities. Interviews have been conducted with the flight crew, cabin crew, airline, airport operator and medical personnel.
AAIB said detailed investigation into the technical and other aspects of the incident is underway. The preliminary report does not establish the probable cause or contributory factors behind the temporary loss of all three hydraulic systems.
