An Air India Airbus A320 carrying 145 people suffered the near-simultaneous loss of all three hydraulic systems while cruising at 36,000 feet on a Phuket-Delhi flight on August 4, triggering an autopilot disconnect, a brief stall warning and an altitude upset that injured 24 people, according to a preliminary report by the Aircraft Accident Investigation Bureau (AAIB).
The report also disclosed that the pilot-in-command tested positive for a psychoactive substance in a confirmatory test conducted after the flight. AAIB described the finding as a “serious concern” and recommended that the Directorate General of Civil Aviation (DGCA) take appropriate action to prevent the abuse of psychoactive substances.
The report, however, does not establish that the pilot’s drug use contributed to the hydraulic failure or the altitude upset. AAIB said its investigation into the technical and other aspects of the accident remains underway.
Flight AI 2379, operated by an Airbus A320-251N registered VT-EXO, departed Phuket International Airport at 01:41 UTC on August 4 with 137 passengers, including three infants, six cabin crew members and two pilots.
At 03:40 UTC, the aircraft entered the Kolkata Flight Information Region and was instructed by air traffic control to climb from 34,000 feet to 36,000 feet.
At 04:02:43 UTC, while cruising at 36,000 feet, the aircraft detected a loss of pressure in its green hydraulic system. Four seconds later, the flight-control system detected the loss of the blue and yellow systems as well.
The autopilot disconnected almost immediately and a continuous repetitive chime sounded. Three seconds later, the aircraft generated a stall warning lasting about two seconds.
The co-pilot, who was flying the aircraft, initially responded to the event before the pilot-in-command took over the controls. During the episode, the aircraft gained about 372 feet and subsequently lost about 292 feet from its assigned altitude.
The blue hydraulic system recovered at about 04:02:52 UTC, followed several seconds later by recovery of the yellow and green systems. Flight-control surfaces subsequently returned to normal operation.
AAIB said the aircraft had been flying at 36,000 feet with the seat-belt signs switched off when the event occurred, leaving passengers and cabin crew vulnerable to the sudden aircraft movement.
The cabin supervisor informed the cockpit crew that passengers and crew members had been injured. The pilots assessed the situation and decided to continue to Delhi rather than divert to the nearest airport.
The crew later requested medical priority from Delhi air traffic control, which provided the necessary assistance.
The aircraft landed safely on runway 11L at Delhi’s Indira Gandhi International Airport at 05:30 UTC and taxied under its own power to its parking bay, arriving at 05:37 UTC.
Airport medical teams treated 24 people, 20 passengers and four cabin crew members. Twenty were discharged after treatment for minor injuries, while four people with serious injuries were admitted to hospitals.
The aircraft itself suffered damage largely confined to the cabin. Investigators documented cracked or deformed ceiling panels, dislodged passenger-service-unit panels, broken handrails, detached overhead-bin doors, a broken emergency-exit handle and a lavatory commode uprooted from its original position.
Pilot tested non-negative for psychoactive substance
The preliminary report separately details the results of post-flight medical testing.
Both pilots underwent breathalyser examinations after arriving in Delhi, with satisfactory results. They were also tested for psychoactive substances.
The co-pilot’s sample was negative. The pilot-in-command’s initial sample was non-negative, and a blood sample was subsequently sent to a pathological laboratory for confirmation. That confirmatory result was also reported as non-negative.
AAIB has not stated what substance was detected or whether it had any operational effect on the flight.
“The confirmation of use of psycho-active substance is a serious concern and AAIB recommends appropriate actions by DGCA on priority,” the bureau said.
In its interim safety recommendation, AAIB said: “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 pilot-in-command, 34, held a valid Airline Transport Pilot Licence and had logged about 5,055 hours of flying, all on the A320. The 32-year-old co-pilot held a Commercial Pilot Licence and had about 1,394 hours of total and A320 flying experience. Both pilots had rested for nearly 22 hours before the flight.
Investigation into hydraulic failure
With no adverse weather reported at the time of the incident, investigators are examining the aircraft’s hydraulic-system failure and other operational factors.
The A320 has three independent hydraulic systems, green, blue and yellow , which normally provide hydraulic power to major flight-control and other aircraft systems.
AAIB said the aircraft’s hydraulic systems recovered within seconds and the flight continued to Delhi, where it landed safely.
The investigation is also examining the aircraft’s maintenance history.
Before departing Phuket, maintenance personnel conducted a pre-flight inspection and recorded no new discrepancies apart from an existing Minimum Equipment List (MEL) item.
The aircraft had been dispatched under MEL item 29-23-01A, relating to the Power Transfer Unit (PTU), which had been invoked on July 28, a week before the incident.
The PTU is an auxiliary source for the green and yellow hydraulic systems and is designed to operate automatically when there is a 500-psi pressure differential between those systems.
AAIB said relevant hydraulic components were removed from the aircraft for further analysis.
The aircraft’s post-flight report recorded warnings including low pressure in the green hydraulic system followed by the blue and yellow systems, autopilot disconnection and flight-control elevator faults.
Both the cockpit voice recorder and flight-data recorder were recovered and downloaded for further analysis.
Weather, crew and further probe
AAIB said no adverse weather was reported by either the flight crew or air traffic control at the time of the event.
Weather forecasts for the Bhubaneswar area, relevant to the aircraft’s position during the altitude upset, did contain provisions for temporary thunderstorms and rain later in the forecast period. However, there was no adverse weather report from the crew or ATC.
The investigation is therefore examining both the aircraft’s technical systems and other operational factors rather than attributing the event to turbulence.
The AAIB has recovered crucial evidence, interviewed the flight and cabin crews and obtained maintenance, operational, fuel and oil records as well as relevant air-traffic-control data.
France’s Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA), representing the state of design and manufacture under international accident-investigation rules, appointed an accredited representative to assist the investigation.
A team of technical experts assigned by Airbus inspected the aircraft in India from August 13 to 15. Investigators subsequently collected hydraulic components and fluid samples for testing.
AAIB said evidence and records obtained from the airline, airport authorities, air traffic control and other stakeholders were still being scrutinised.
The bureau stressed that its investigation was intended to determine the probable causes and contributing factors and “not to apportion blame or liability”.
The report is preliminary and subject to change. A final report will be issued after the investigation is completed.
(With inputs from PTI)