Air India Phuket-Delhi Jet Lost Control for Four Seconds

An Air India Airbus A320 flying from Phuket to Delhi briefly lost control of key flight surfaces for about four seconds during a sudden altitude drop on August 4, according to initial findings from aircraft manufacturer Airbus. The aircraft lost around 300 feet of altitude during the incident before stabilising and continuing to Delhi.

The preliminary findings mark a significant development in the Investigation because the incident was initially attributed by Air India to severe turbulence. Analysis of the aircraft’s flight data recorder has now indicated that all three hydraulic systems experienced losses, while the elevators and ailerons became unavailable for approximately four seconds.

The flight, AI 2379, was carrying 137 passengers. Twenty passengers and four cabin crew members were severely injured, while 17 people were hospitalised after the aircraft experienced the sudden altitude change. Despite the loss of control inputs, the aircraft recovered and landed safely in Delhi.

What Airbus found during its initial investigation

Airbus has been assisting the Aircraft Accident Investigation Bureau (AAIB), along with the French aviation accident investigation authority, in examining what happened aboard the Phuket-Delhi flight.

Following analysis of the flight data recorder, Airbus found that the aircraft’s flight controls were briefly affected after losses occurred across all three hydraulic systems.

The elevators and ailerons were unavailable for around four seconds, according to the interim findings. These are critical flight-control surfaces. Elevators help control an aircraft’s pitch, while ailerons control its roll.

The autopilot also disengaged briefly during the event. The combination of hydraulic-system problems and the temporary loss of important flight controls helps explain why the aircraft experienced a sudden change in altitude.

However, the findings do not yet establish why the hydraulic systems experienced the losses in the first place. Airbus has asked Air India to carry out a detailed inspection of the aircraft as investigators continue looking for the underlying cause.

How hydraulic systems affect an aircraft

Hydraulic systems play a critical role in controlling many aircraft functions. They provide the force required to move important flight-control surfaces and operate other aircraft components.

On a modern passenger aircraft, the systems are designed with redundancy so that the loss of one system does not normally mean an immediate loss of aircraft control. The significance of the AI 2379 incident lies in the reported loss of all three hydraulic systems at the same time.

Airbus’s initial findings indicate that the hydraulic systems eventually recovered. During the period when the systems were affected, however, the aircraft’s elevators and ailerons were unavailable for approximately four seconds.

That short period was enough to coincide with a rapid change in altitude and a serious onboard event. For passengers and crew, a sudden loss of approximately 300 feet can result in significant forces and injuries, particularly when people are not prepared for the aircraft’s movement.

Why the aircraft suddenly lost altitude

Airbus also identified a “full nose-down input” during the event. In simple terms, this means the aircraft received an input that caused its nose to move downward, resulting in a downward pitch.

The finding is important because it provides investigators with additional flight-data evidence about what occurred during the four-second period. It does not, by itself, explain the root cause of the incident.

Investigators still need to establish why the aircraft received the nose-down input and how that input was connected to the hydraulic-system losses and temporary unavailability of the flight controls.

The sequence of events matters because an aviation investigation typically needs to distinguish between what happened and why it happened. The available interim findings describe several events recorded during the flight, but they do not yet provide a final explanation for the entire chain.

Eleven system alerts recorded within minutes

The aircraft’s post-flight maintenance report recorded 11 system alerts within a period of roughly two to three minutes, according to sources cited in the report on the incident.

The concentration of multiple alerts in such a short period is another important part of the investigation. It indicates that the aircraft experienced several system-related indications around the time of the event.

However, the presence of multiple alerts does not automatically identify the root failure. Investigators must determine which warnings were primary, which may have resulted from the same underlying problem, and how the aircraft systems responded.

This is one reason Airbus has requested a detailed inspection of the aircraft. Flight-data analysis can establish what the aircraft systems were doing during the event, while physical inspections can help investigators determine whether a component, sensor, hydraulic system or another technical issue contributed to the failure.

Airbus says the root cause has not yet been identified

Airbus has acknowledged technical issues in connection with the incident but has not yet established the underlying cause.

In its communication to Air India, Airbus said that it understood the flight had experienced a sudden loss of altitude on August 4 and that checks of the aircraft’s systems and sensors were required to provide more information.

That distinction is important. The interim findings identify a temporary loss of flight-control availability and hydraulic-system problems, but investigators have not yet determined what caused the three hydraulic systems to lose functionality at the same time.

A final conclusion could therefore depend on the results of the aircraft inspection, additional analysis of recorded data and the broader investigation being conducted by the AAIB and its supporting organisations.

Air India initially blamed severe turbulence

The latest technical findings also change the context surrounding the airline’s initial explanation of the event.

Air India had initially attributed the sudden altitude loss to severe turbulence. The Airbus analysis now indicates that the aircraft experienced a temporary technical problem involving its hydraulic systems and flight controls.

That does not necessarily mean turbulence played no role. Rather, the available findings show that investigators are examining a more complicated sequence involving aircraft systems, control inputs and the temporary loss of key flight-control functions.

Until the investigation is completed, it would be premature to assign a single cause to the incident. The technical findings are interim and remain part of an ongoing investigation.

Captain’s positive marijuana test adds another line of inquiry

The investigation has also drawn attention to the captain’s post-incident marijuana test. The captain tested positive for marijuana after the flight, but that result alone does not establish that the pilot was impaired during the incident or that marijuana contributed to the aircraft’s loss of altitude.

Both pilots have been de-rostered pending the investigation.

The issue has nevertheless prompted Air India to introduce a wider testing measure. According to an internal communication seen by Reuters, the airline ordered mandatory drug tests for all its pilots following the incident.

The testing issue and the aircraft’s technical problems should be considered separately unless investigators establish a connection between them. A positive test result does not, on its own, establish impairment at the time of the flight.

Why the four-second loss of control matters

Four seconds may appear extremely brief, but in aviation, the availability of flight controls can be critical even over a very short period.

During the AI 2379 incident, the elevators and ailerons were reportedly unavailable for about four seconds while the autopilot also briefly disengaged. The aircraft then recovered as the hydraulic systems eventually returned.

The incident therefore highlights the importance of system redundancy and the ability of an aircraft to recover from simultaneous or cascading technical problems. It also shows why investigators examine flight-data recorder information in such detail: a sequence lasting only a few seconds can contain crucial evidence about what happened.

For passengers, the most visible consequence was the sudden altitude change and resulting injuries. For investigators, however, the key questions involve the exact order of hydraulic-system losses, flight-control availability, autopilot disengagement and the nose-down input.

What investigators will examine next

The next stage of the investigation is likely to focus on identifying the root cause behind the hydraulic-system losses and determining how the different aircraft systems interacted during the incident.

Airbus has already requested a detailed inspection of the aircraft. Checks of systems and sensors will form an important part of that process.

Investigators will also need to reconcile the physical condition of the aircraft with information captured by the flight data recorder and the maintenance alerts recorded after the flight.

The central questions include:

• Why did all three hydraulic systems experience losses?
• What caused the elevators and ailerons to become unavailable?
• What triggered the full nose-down input?
• Why did the autopilot disengage?
• What caused the 11 system alerts recorded around the event?
• How did the aircraft’s systems recover sufficiently for the flight to continue to Delhi?

These questions cannot be answered conclusively from the interim findings alone. The investigation must establish the relationship between the individual events before a final cause can be determined.

What the incident means for Air India

The Phuket-Delhi incident presents Air India with both an operational and safety challenge. The airline must cooperate with the ongoing investigation while also ensuring that the aircraft involved undergoes the inspections requested by Airbus.

The decision to de-roster both pilots pending investigation and introduce mandatory dope testing for pilots also demonstrates the airline’s response to the broader concerns raised by the incident.

However, the technical findings remain central. The discovery of simultaneous hydraulic-system losses means that understanding the aircraft’s technical condition and the precise cause of the control disruption will be essential to the final investigation.

Final investigation could provide a clearer picture

The interim Airbus findings provide a substantially more detailed picture of the four-second period than was initially available. Investigators now know that the aircraft experienced losses in all three hydraulic systems, that key flight controls became unavailable, that the autopilot briefly disengaged and that a full nose-down input occurred as the aircraft lost altitude.

But those findings are not the final answer.

The root cause behind the hydraulic-system losses remains unidentified, and further inspection of the aircraft’s systems and sensors is required. The AAIB investigation, supported by Airbus and the French aviation accident investigation authority, will ultimately need to establish how the failures occurred and whether they were connected.

For now, the most significant takeaway is that the August 4 incident was not simply a matter of passengers encountering a rough patch of air. The interim technical findings point to a brief but serious disruption involving multiple aircraft systems, followed by recovery that allowed the A320 to land safely in Delhi.

Until investigators complete their work, the precise cause of the sudden altitude loss remains unresolved. The forthcoming technical inspection and final investigation findings will be crucial in determining what went wrong and what measures may be needed to prevent a similar event in the future.