Air India Phuket-Delhi flight lost hydraulics for seconds: Airbus asks airline to check if it was genuine failure or glitch

The Air India Airbus A320 flight from Phuket to New Delhi, which rapidly lost around 300 feet of altitude on August 4, injuring 24 people, briefly lost hydraulic control across all three of its independent systems, leaving pilots struggling for control for a few seconds, the initial assessment of the flight data recorders by Airbus, reviewed by ET, showed.

It is yet to be ascertained whether the hydraulics failed or it was a spurious warning caused by a faulty wire or sensor. Airbus has asked Air India to physically check one of the hydraulic pressure switches to determine if it was faulty and sent a spurious signal.

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The incident was termed “rarest of rare” by pilots and engineers familiar with the A320, and may invite scrutiny of one of the most widely used aircraft in the world. IndiGo and Air India together operate more than 500 A320 family aircraft, with around 1,300 on order.

Non-responsive Ailerons

Airbus has not prescribed any pilot action for such a situation, as it considers simultaneous malfunction of all three hydraulic systems impossible.

While the captain is separately under scrutiny after testing non-negative for psychoactive substances, the initial assessment from the recorders does not indicate any human action as a cause of the incident. Aircraft Accident Investigation Bureau (AAIB), which is investigating the incident, has already interviewed the pilots. The A320 has three independent hydraulic systems, colour-coded Green, Blue and Yellow, designed so that failure of one does not result in loss of aircraft control.

In the Air India flight, all three hydraulic gauges registered a pressure drop within one second, causing the elevators and ailerons to briefly stop responding to pilot commands. The two ailerons, located on the outer parts of each wing, normally move in opposite directions, reducing lift on one side while increasing it on the other, to roll the aircraft left or right. The elevators, on the horizontal tail at the rear, control the aircraft’s nose up or down.

In this case, the ailerons moved in the same direction, generating extra lift that pushed the aircraft’s nose upward steeply without any pilot input. The autopilot disengaged, as it is designed to do in abnormal conditions. The first officer took manual control and pushed the nose down sharply, causing a rapid downward acceleration that threw passengers and cabin crew upward, leading to the injuries.

Five seconds later, pressure was restored across all three systems, the flight control computers reconnected, and the aircraft began responding to pilot commands again. The captain told the DGCA in his post-flight report that he was standing behind the first officer’s seat discussing the aircraft’s air conditioning system when the situation emerged. The pilots did not divert to the nearest airports, Varanasi or Lucknow, and continued to Delhi, around two hours away, despite reports of injuries on board.