Air India Phuket-Delhi flight incident report cites hydraulic failure

The preliminary report of the investigation into the sudden altitude loss incident involving an Air India Airbus A320 aircraft — VT-EXO — on August 4 has flagged a sudden hydraulic systems failure as well as the non-negative drug test report of the pilot-in-command. The Aircraft Accident Investigation Bureau (AAIB), which is probing the incident, issued a recommendation to aviation safety regulator Directorate General of Civil Aviation (DGCA) to take appropriate actions as deemed fit to prevent abuse of psychoactive substances.

While the investigation remains underway and the preliminary report hasn’t identified any definitive likely cause, it focussed on a sudden and brief triple hydraulic failure and the PIC’s drug test. On August 14, The Indian Express had reported that an initial assessment of the digital flight data recorder (DFDR) data by Airbus had indicated that the aircraft experienced a temporary loss of all three hydraulic systems, which led to loss of key aircraft control surfaces for about four seconds. “Detailed investigation regarding technical and other aspects are underway.

In this case, it has been observed that the PIC was found non-negative for psycho-active substance in the confirmatory test. The confirmation of use of psycho-active substance is a serious concern and AAIB recommends appropriate actions by DGCA on priority. The preliminary report is published as per ICAO (International Civil Aviation Organization) guidelines.

The investigation is under progress. The final report will be published in due course,” the preliminary report said. The Air India Airbus A320 aircraft operating a flight from Phuket to Delhi on August 4 encountered a sudden altitude drop of about and caused injuries to 20 passengers and four cabin crew members, and 17 of the 24 had to be hospitalised.

The aircraft had 137 passengers, six cabin crew members, and two pilots on board. Also Read | After Air India drug incident, DGCA weighs annual testing of all pilots The government and the airline had initially attributed the incident to severe turbulence, although it was later learnt that the incident was unlikely to have been weather-related.

The preliminary report now also states that the pilots and the air traffic control (ATC) didn’t report adverse weather. Conduct of the pilots has also been under scanner, particularly in view of the PIC’s non-negative confirmatory drug test report, which has now been confirmed by the AAIB preliminary report.

According to sources, the PIC had tested positive for marijuana. A series of snags involving the aircraft’s hydraulic systems and flight control surfaces have emerged as a key focus area for investigators. The Airbus A320 aircraft has three independent hydraulic systems — coded green, blue, and yellow — built as a redundancy so that the loss of one such system doesn’t result in total loss of hydraulic control.

Hydraulic pressure is essential for moving several of the aircraft's flight-control surfaces. According to experts, the simultaneous loss of the three hydraulic systems was virtually considered an impossibility on the A320, one of the most flown aircraft types globally. Notably, the aircraft had been dispatched under a Minimum Equipment List (MEL) item related to the power transfer unit (PTU), which had been invoked about a week prior to the accident.

The PTU is one of the auxiliary power sources for two of the three hydraulic systems on an Airbus A320 jet. When an aircraft is dispatched under an MEL, it means the flight is departing with a known non-functioning part or system. This is not a safety violation, and is a strictly regulated process with well laid-out procedures to ensure that the aircraft is dispatched in a safe and airworthy condition.

It is highly common globally for aircraft to be released under MEL. According to the preliminary report, the incident occurred while the aircraft was cruising at 36,000 feet at 09:32:43 am India time, when the aircraft’s flight control system detected loss of green hydraulic system.

About four seconds later, loss of blue and yellow hydraulic systems was detected, followed by the autopilot getting disengaged. Shortly thereafter, the stall warning triggered for two seconds. “The Co-Pilot, who was the Pilot Flying (PF) responded and tried to control the prevailing situation.

Subsequently, PIC took over the controls. Meanwhile, the aircraft encountered altitude upset. Initially, it gained 372 ft and fell by 292 ft from its assigned FL360 during the event,” the preliminary report said. Also Read | After pilot tests positive for marijuana, Air India group orders one-time dope test on its 5,000 pilots “At around 04:02:52 UTC (09:32:52 India time), the Blue hydraulic system was recovered, and few seconds later, the Yellow hydraulic and the Green hydraulic systems were also recovered.

Consequently, this led to the recovery of the Flight control (F/CTL) surfaces. Subsequently, the aircraft operation returned to its normal operating condition,” the report added. It noted that since seatbelt signs were off at the time of the incident, some passengers and cabin crew members sustained injuries. “The flight crew assessed the cabin situation and took the decision of continuing the flight to its planned destination i.e.

Delhi airport and did not divert to the nearest enroute airport. Later, the flight crew contacted ATC Delhi and sought medical priority. ATC responded accordingly and provided requisite assistance. At 05:30 UTC aircraft landed safely on runway 11 L at IGI airport, Delhi,” the report said.

Following the release of the preliminary report, Air India said that it continues to extend full cooperation to the investigation, including providing access to all relevant operational, maintenance and technical records. “Our pilots undergo rigorous training, regular proficiency checks, medical examinations and other regulatory assessments in accordance with applicable national and international requirements.

Following the incident, Air India has started voluntary testing of 100% of its pilots as a further step to reinforce its safety-first approach. The airline maintains zero tolerance for any breach of safety, fitness or regulatory requirements and will take appropriate action wherever warranted.

Air India remains committed to implementing any recommendations arising from the investigation,” an Air India spokesperson said.