The August 4 Air India Phuket-Delhi flight suffered a sudden altitude upset after all three hydraulic systems of the Airbus A320neo were lost within seconds, according to a preliminary report by the Aircraft Accident Investigation Bureau (AAIB).
The report also revealed that the pilot-in-command (PIC), who was the pilot monitoring during the incident, tested “non-negative” for a psychoactive substance in a confirmatory test. The co-pilot tested negative in both tests.
The AAIB, however, did not establish any connection between the psychoactive substance finding and the aircraft’s altitude upset. It said a detailed investigation into the technical and other aspects of the incident is still underway.
The flight was carrying 137 passengers, with 20 passengers and four crew members injured after the aircraft suddenly lost altitude while cruising at 36,000 feet.
AAIB recommends action over psychoactive substance use
The AAIB has recommended that the Directorate General of Civil Aviation (DGCA) take appropriate action to prevent the abuse of psychoactive substances among flight crew.
The report said both pilots underwent post-flight medical examinations in Delhi because the flight had originated outside India. Their breathalyser tests for alcohol were satisfactory.
Both pilots were subsequently subjected to psychoactive substance detection tests. The PIC’s initial sample was found to be non-negative, and a confirmatory blood test also returned a non-negative result. The co-pilot tested negative in both tests.
The AAIB described the use of psychoactive substances by flight crew as a serious concern.
What happened during the Air India flight?
The aircraft took off from Phuket at 7:11 am IST and initially reported no abnormalities.
While cruising at FL360, or around 36,000 feet, the aircraft’s flight-control system detected a loss of the green hydraulic system at approximately 9:32 am.
Four seconds later, the blue and yellow hydraulic systems were also detected as having been lost.
The autopilot subsequently disengaged and a continuous repetitive chime sounded. Three seconds later, the stall warning was triggered for two seconds.
The AAIB said the aircraft then experienced an “altitude upset”, initially climbing 372 feet and subsequently descending 292 feet from its assigned flight level during the event.
The hydraulic systems were restored within seconds, allowing the flight-control surfaces to recover and the aircraft to return to normal operating conditions.
Co-pilot responded before PIC took control
According to the preliminary report, the co-pilot responded to the situation before the PIC took over the aircraft’s controls.
The crew assessed the situation and decided to continue towards Delhi rather than divert to the nearest airport.
The flight crew and air traffic control did not report any adverse weather at the time of the incident.
The crew later contacted Delhi ATC and requested medical priority. The aircraft landed safely at around 11 am IST and taxied to its parking bay under its own power.
Four seriously injured people were hospitalised, while the aircraft’s cabin sustained damage, particularly to overhead stowage bins and ceiling panels.
Investigation into hydraulic failure underway
The aircraft’s post-flight report recorded warnings of low pressure in the green hydraulic system, followed by the blue and yellow systems.
It also recorded the autopilot disengaging and faults involving the left and right elevators, along with low-level warnings for the yellow and blue hydraulic reservoirs.
The AAIB removed both the aircraft’s flight data recorder and cockpit voice recorder for further analysis.
Investigators also inspected the aircraft, collected hydraulic components and fluid samples, and obtained fuel and oil samples. Maintenance and operational records, along with relevant information from Delhi and Kolkata ATC, were also collected.
Technical experts from Airbus inspected the aircraft between August 13 and 15, while additional hydraulic components and samples were collected for examination.
Air India begins 100% pilot testing
Air India said it would continue to fully cooperate with the AAIB investigation and provide access to operational, maintenance and technical records.
Following the incident, the airline also began voluntary testing of 100% of its pilots as part of its safety measures.
Air India said it maintains zero tolerance for breaches of safety, fitness or regulatory requirements and would take appropriate action wherever warranted.
The government is also considering annual random drug testing for all pilots. Existing rules provide for testing of 10% of the overall pilot network, while Air India’s voluntary initiative covers all its pilots.
Pilots’ association seeks answers on hydraulic failure
Airlines Pilots’ Association India (ALPA India) president Sam Thomas said the preliminary report was broadly on expected lines but called for an expedited process to restore the co-pilot’s flying status.
He also sought Airbus’s assessment of why all three hydraulic systems failed, even if only briefly, and what modifications could prevent a recurrence.
Thomas called for a time-bound final investigation report and action in the event of a proven second-time positive drug test involving a pilot.
Airbus said it continues to provide technical assistance to the relevant investigating authorities and is supporting Air India with additional information as it becomes available.
The AAIB’s preliminary findings do not represent a final determination of the cause of the incident. The detailed investigation will examine both the hydraulic-system failure and other contributing factors.
