Airbus’ initial assessment shows that the pilots had to contend with a loss of normal flight-control response for several seconds after the Phuket-Delhi A320 experienced a sequence of hydraulic-system pressure losses, sources told CNBC-TV18.

The First Officer applied full nose-down input after the aircraft’s control surfaces did not immediately respond, according to the Airbus dossier reviewed by CNBC-TV18.

The incident involved an Airbus A320 operating an Air India Phuket-Delhi service on August 4. The aircraft experienced a sudden change in altitude during the flight, leaving passengers and crew members injured. Airbus has now shared an initial assessment based on its analysis of the aircraft’s Digital Flight Data Recorder (DFDR).

According to the Airbus dossier, the aircraft’s Green hydraulic system was lost first, followed by the Blue and Yellow systems. The A320 has three hydraulic systems that provide power to key flight controls, with the architecture designed to provide redundancy.

In simple terms, hydraulic pressure helps move several of the aircraft’s control surfaces. The elevators at the tail help move the nose up or down, while the ailerons on the wings control the aircraft’s roll.

The Airbus assessment says the loss of hydraulic pressure resulted in the temporary loss of normal operation of the elevators and ailerons for around four seconds.

The dossier then describes what happened in the cockpit. Airbus records that AP2, or Autopilot 2, was disconnected, after which full nose-down input began to be applied from the First Officer’s side. The assessment says there was initially no direct response from the flight-control surfaces.

In simpler terms, the First Officer was commanding the aircraft to bring its nose down, but the aircraft’s control surfaces did not immediately respond in the normal manner.

Airbus also says the ailerons moved towards their “zero hinge moment” position during the hydraulic-system issue. This technical term essentially describes the ailerons moving towards a position where they were no longer providing their normal control input. Airbus says this resulted in an increase in the aircraft’s pitch, or the nose moving upwards.

The hydraulic systems subsequently recovered, and the affected flight-control surfaces also returned to normal operation, according to the Airbus assessment. The pilots were then able to regain normal control of the aircraft.

However, the Airbus dossier does not identify a definitive root cause for the hydraulic pressure loss. Instead, Airbus has asked Air India to carry out further checks.

The manufacturer has sought operational tests of the Green, Blue and Yellow hydraulic systems, along with checks of their pressure switches and pressure transducers. Airbus has also asked Air India to remove and identify certain pressure transducers and leak-measurement switches installed on the aircraft. The dossier adds that further wiring checks may be required.

We have reached out to Airbus and Air India for comment on the story. Queries remained unanswered at the time of publication.