“When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” – Sherlock Holmes, The Sign of the Four
On 4 August 2026, Air India AI2379, an Airbus A320neo VT-EXO, was cruising from Phuket to Delhi at 36,000 feet when Green hydraulic pressure disappeared, followed within seconds by Blue and Yellow. The autopilot disconnected, a stall warning sounded, the aircraft pitched violently and 24 people were injured. Within seconds, the hydraulic systems recovered and the aircraft landed safely. So, what actually happened? Can three completely independent hydraulic systems fail almost simultaneously?
Yes – but extraordinarily rare. (occurred once earlier, read below)
Can all three then recover almost together?
Possible, perhaps.
But if so, what mechanism caused it? That is where the investigation now starts to become interesting.
The A320’s three hydraulic systems are designed with substantial redundancy. Green and Yellow are normally powered by engine-driven pumps; Blue has its own electric source. The preliminary report now also identifies a maintenance issue involving the Power Transfer Unit (PTU), which provides hydraulic power between the Green and Yellow systems. The aircraft had been operating with a PTU-related MEL item. This is important, but it is equally important to state here clearly what it does not mean. The PTU issue is documented. It has not been established as the cause of the incident. A genuine simultaneous failure demands a very credible common mode explanation. So one obvious possibility is that the normal hydraulic switches were selected OFF. But those controls are directly in front of the pilots. Then there is another possibility: the leak-measurement valve switches on the maintenance panel behind the pilots were turned off. Since these are just for maintenance, and intended for ground leak testing by engineers alone and not for normal flight operations they have been placed far behind by the manufacturer, out of reach of either pilot. In fact, not many pilots really know what it does and it is not part of any contingency checklist. Their exact, position, accessibility, configuration and effect on the hydraulic system of VT-EXO must be reconstructed.
Time to address those questions then…
Firstly, could operating these very switches Hydraulic Leak Valve) reproduce the AI2379 sequence? Why theorise alone, let’s try and reproduce it. If a controlled test by investigators demonstrates that the Green-Blue-Yellow sequence, the autopilot disconnect, the loss of hydraulic control and subsequent recovery can be replicated by manipulating those hydraulic leak valves (remember: which were never ever designed to be operated by the pilots and were for engineers alone) investigators would have a potentially decisive technical lead. It would not, by itself, prove who operated them or why.
Secondly, who could physically reach these unreachable switches? Well if operating them required someone to leave the normal seated position to stand behind the seats, that will be established in conjunction with CVR records detailing the discussion between the pilots at that moment, (were they discussing the PTU MEL), the actual recorded seat position on the electric rails would provide evidence and FDR would establish whether either pilot was moving around in the cockpit at that precise moment.
Thirdly, How often has this dangerous multiple failure occurred on this type of airplane (Airbus 319/320/321). This takes us back in to the history books. The only other event ever in the fleet was on 9th July 2012, when Air India AI940, an Airbus 319 flying from Abu Dhabi to Delhi, diverted to Nawabshah, Pakistan, after the commander reported a triple hydraulic failure. The next day’s morning paper (Times of India) termed it as the “rarest of the rare” event. The subsequent investigation found that all three hydraulic systems were functioning normally and identified the issue as only a cockpit indication problem. Why do I bring this up? It is the only known triple hydraulic failure in the 39 years of flying. I dug in a little deeper, the written record clearly establishes that the commander of that flight was the father of this very captain, involved in the AI 2379 incident. That does not prove a damn thing about AI 2379. But it is simply stated an extraordinary coincidence that investigators should examine.
Fourthly, was the PIC in anyway impaired in anyway? Probably. Since he tested “non-negative” for a psychoactive substance in confirmatory testing, which post a little legal wordplay means he tested positive. That is serious, but it does not establish impairment as the cause of the hydraulic event. However does a higher altitude (cabin altitude of 7000- 8000 feet at a cruising altitude of 36000) possibly play a role in affecting a person’s mental and physical abilities?
Frankly, if someone asks me whether three independent hydraulic systems could simply disappear and then almost magically come back, my answer is deliberately blunt: Highly improbable. One will need marijuana to believe that. The answer, however, cannot come from opinion alone and must come from data. What did the FDR record? Did the CVR capture and record the pilots discussing the same hydraulic system and PTU issue before this rare event? What were the hydraulic pressures? What were the pilots’ positions and control inputs? Were the leak valve switches moved? Can the entire sequence be reproduced? Can forensics be used to check if fingerprint evidence establishes as to who operated the hydraulic leak valve switches last.
Let’s come to the stall warning and the recovery by the first officer.
The THS (Trimmable Horizontal Stabiliser) on this airplane, positions the aft stabiliser in the slightly nose up position in cruise. In normal conditions, when hydraulics have not done a disappearing act, the autopilot automatically maintains the aircraft level on its flight path. Should all hydraulics magically disappear, the autopilots will disconnect as it happens here and now the aircraft leaves its desired flight path and starts climbing. This climb is in response to the slight nose up trim of the THS in cruise flight. So for the common man and woman, the angle of the aircraft tilts or increases further back in relation to the horizon. This may lead to an undesirable aircraft state where the aircraft is now fast approaching a likely stalled condition. The super computers onboard pick this up and generate a stall warning and the well trained pilots in the cockpit, move the joy stick forwards (nose down) to reduce this increasing angle of attack to recover and return to safe flight.
But what happens if all hydraulics has vanished. Unlike conventional aircraft where push pull rods and cables are physically connected from the pilots control column to the control surfaces, the Airbus series is a “Fly by Wire” machine with the latest technology. So during recovery if the sidestick is moved forward to reduce this increasing angle of attack, the airplane cannot respond because there is no hydraulic pressure to help move the controls. If the pilot (First Officer) sees no appreciable nose down movement, he does what you and I would do; Increase the deflection by moving this sidestick even further down, commanding nose down recovery action. Now in say 5-6 seconds hydraulic pressure is magically restored!!!, then the full force of all hydraulics must immediately fulfil demands made by the pilot and move the controls to the commanded deflection. This causes a violent nose down pitching moment, which causes a negative G situation. (Yes, the same feeling one gets when you jump off a high ledge or that 10 meter board into a swimming pool below). Everything unbuckled, unfastened and not secure now must follow basic physics and hence moves up while the cabin floor seems to disappear below you. This is not turbulence and the weather Gods didn’t play foul.
Finally the question that remains is not, “How did three hydraulics systems fail one after the other in seconds?” It is “What made three independent systems behave as though they had been switched off and then switched back on?” The answer: Elementary
In aviation, coincidences are investigated. Systems are tested. Datais followed. And when the impossible has been eliminated, what remains, – however improbable, must be confronted.
Captain Akshay
06 September 2026
