An Air India Airbus A320 briefly stopped responding to pilot commands after all three of its independent hydraulic systems registered a pressure drop within one second, according to an initial Airbus assessment of flight-recorder data reviewed by the Economic Times.
The finding offers the clearest technical account yet of the August 4 incident aboard flight AI2379 from Phuket to Delhi. The aircraft rapidly lost around 300 feet of altitude, leaving 20 passengers and four cabin crew members injured.
It does not, however, establish the cause.
Investigators are yet to determine whether hydraulic pressure actually collapsed across the aircraft or whether a defective switch, wire or sensor generated false readings. Airbus has asked Air India to physically inspect one hydraulic pressure switch to establish whether it sent a spurious signal, ET reported.
The A320 has three independent hydraulic systems, identified as Green, Blue and Yellow, which power several critical components, including the aircraft’s flight-control surfaces.
The separation is designed to ensure that a problem in one system does not deprive pilots of control.
During the AI2379 incident, all three systems indicated a pressure drop within one second, according to the ET report. The aircraft’s elevators and ailerons then briefly stopped responding to commands from the cockpit.
Elevators, located on the horizontal tail, control whether the aircraft’s nose moves up or down. Ailerons on the wings ordinarily move in opposite directions to roll the aircraft.
In this case, the ailerons moved together in a way that increased lift and caused the aircraft’s nose to rise sharply without a corresponding pilot command, ET reported. The autopilot disconnected as the abnormal sequence unfolded.
The first officer, who was flying the aircraft, assumed manual control and pushed the nose down. The sharp correction produced rapid downward acceleration, throwing passengers and cabin crew upward and causing the injuries.
Pressure indications returned across all three hydraulic systems about five seconds later. The flight-control computers reconnected and the aircraft began responding normally again, according to the report.
Pilots and engineers familiar with the A320 described the sequence to ET as exceptionally rare. The report said Airbus procedures do not prescribe a specific crew response to the simultaneous loss described because the aircraft’s redundant architecture is intended to prevent such a situation.
The distinction between a genuine pressure collapse and an erroneous warning is now central to the investigation.
A physical inspection of the pressure switch and associated components could show whether the aircraft actually lost hydraulic power or whether its computers reacted to incorrect information.
India’s Civil Aviation Ministry has confirmed that the aircraft, registered VT-EXO, experienced an altitude variation of approximately 300 feet before stabilising and landing safely in Delhi. It was carrying 137 passengers, including three infants, and eight crew members. The ministry’s updated statement placed the number of injured at 24.
The captain said in his post-flight account that he was standing behind the first officer’s seat and discussing the aircraft’s air-conditioning system when the warnings appeared, ET reported.
The initial Airbus assessment did not identify any human action as the trigger for the loss of control, according to the report.
The captain is separately under scrutiny over his post-flight screening for psychoactive substances. Reuters reported, citing a source familiar with the matter, that a confirmatory test returned positive for marijuana. Neither the government nor investigators have linked that result to the altitude incident. Reuters reported that both pilots were removed from flying duty pending the inquiry.
ET also reported that the pilots did not divert to Varanasi or Lucknow after the incident and instead continued to Delhi, then around two hours away, despite injuries aboard the aircraft.
The Aircraft Accident Investigation Bureau is examining the aircraft and its systems, recorded flight data, maintenance records, medical information and accounts from those involved.
France’s BEA, representing the aircraft’s country of design and manufacture, and Airbus are providing technical assistance.
The AAIB has cautioned against drawing conclusions from isolated information before it completes its examination of the technical, operational, medical and human factors involved.
Any wider implications will depend on whether investigators establish a genuine common technical fault. The question carries particular significance for India because Air India and IndiGo together operate more than 500 A320-family aircraft and have around 1,300 more on order, according to ET.
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