An Air India flight travelling from Phuket to Delhi experienced a temporary loss of pressure across all three hydraulic systems during the flight on August 4, 2026, according to a preliminary investigation by the Aircraft Accident Investigation Bureau (AAIB).
The incident involved Air India flight AI 2379, which was carrying 137 passengers. The aircraft was flying at Flight Level 360 when its flight-control system detected a pressure loss in the green hydraulic system. The blue and yellow systems also lost pressure shortly afterwards.
The hydraulic disruption caused the autopilot to disconnect, while a continuous repetitive chime was heard in the cockpit. A stall warning was also activated for about two seconds.
Aircraft Experienced Altitude Upset
During the incident, the aircraft briefly climbed 372 feet above its assigned level before descending 292 feet from FL360. The hydraulic systems later regained pressure, allowing the flight-control surfaces to operate normally.
The co-pilot was flying the aircraft when the problem began and initially handled the situation. The pilot-in-command (PIC) subsequently took control.
The sudden altitude change also caused people inside the cabin to be thrown around. Since the seat-belt signs were switched off at the time, 20 passengers and four cabin crew members sustained injuries requiring medical attention after the aircraft reached Delhi.
Twenty of those treated were later discharged after suffering minor injuries, while four people with serious injuries were admitted to hospital.
The aircraft itself sustained damage to several cabin fittings, including overhead ceiling panels, passenger-service units and overhead-bin doors. An emergency-exit handle and handrails were also damaged, while a lavatory fixture was uprooted and parts of crew seats were broken.
Flight Continued To Delhi
Despite the incident, the crew decided to continue towards Delhi rather than divert to an airport along the route.
As the aircraft approached the national capital, the crew informed Delhi Air Traffic Control about the situation and requested medical priority. The flight landed safely on Runway 11L at Indira Gandhi International Airport at around 11 am and reached its parking bay at 11:07 am under its own power.
The AAIB said there were no adverse weather conditions when the incident occurred, although weather forecasts had indicated a possibility of thunderstorms later.
Investigators also found that the aircraft was operating under an existing Minimum Equipment List (MEL) item related to its Power Transfer Unit (PTU). The MEL item, identified as 29-23-01A, had been invoked on July 28. No fresh discrepancy had been reported before the aircraft departed Phuket.
AAIB Raises Concern Over Pilot’s Test
The preliminary investigation has also highlighted a separate issue involving the pilot-in-command.
Both pilots initially underwent breathalyser tests, with both returning negative results. They were then subjected to psychoactive-substance screening.
According to the AAIB, the PIC’s initial sample was non-negative, while the co-pilot’s result was negative. Blood samples were subsequently sent to a laboratory for confirmation.
The confirmatory test again returned a non-negative result for the PIC, while the co-pilot’s blood sample remained negative.
The AAIB described the finding concerning the PIC as a serious concern and recommended that the Directorate General of Civil Aviation (DGCA) take appropriate action on the matter as a priority.
However, the preliminary report does not establish any connection between the pilot’s test result and the hydraulic-system failure or the aircraft’s altitude upset.
Investigation Into Cause Still Underway
The AAIB has recovered the cockpit voice recorder and digital flight data recorder from the aircraft, and the recorded information has been downloaded for detailed examination.
Investigators have also collected hydraulic components and fluid samples for testing. Technical specialists from France’s Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA) and Airbus examined the aircraft between August 13 and 15.
Maintenance and operational documents, along with fuel and oil samples and information from air traffic control authorities, have also been collected. Investigators have interviewed members of the flight crew and cabin crew as well as representatives of the airline, airport operator and medical teams.
The AAIB said its investigation into the technical and other aspects of the incident remains in progress.
The preliminary report does not determine the probable cause of the triple hydraulic-system pressure loss or identify contributory factors. Those findings will be established only after the investigation is completed and the final report is issued.
