AAIB: Air India AI 2379 lost all three hydraulics at 36,000 feet

Air India flight AI 2379 lost pressure in all three hydraulic systems within seconds while cruising at 36,000 feet on 4 August. The Aircraft Accident Investigation Bureau said so in a preliminary report released on 4 September. The Airbus A320-251N, registered VT-EXO, was flying from Phuket to Delhi with 137 passengers, three of them infants, six cabin crew and two pilots. Twenty-four people were hurt, four of them seriously. The jet landed in Delhi.

The sequence is on the flight-data recorder. At 04:02:43 UTC, already inside the Kolkata Flight Information Region, the flight-control system flagged a loss of pressure in the green hydraulic circuit. Four seconds later it flagged the blue and yellow circuits as well. At 04:02:48 the autopilot dropped out and a continuous repetitive chime sounded. Three seconds after that a stall warning sounded for two seconds.

The co-pilot was flying. He tried to hold the aircraft. The 34-year-old captain then took the controls. The jet climbed 372 feet above its assigned level, Flight Level 360, then sank 292 feet below it, a swing of 664 feet. The blue system came back first, then yellow and green. Control surfaces worked again. The rest of the flight was flown by hand and by a restored autopilot to a normal landing.

The same preliminary report recorded a non-negative drug test on the captain after landing. AAIB called that result a serious concern and told the Directorate General of Civil Aviation to act on priority. The bureau did not say the test caused the hydraulic failure. It also did not name the substance beyond calling it psychoactive. A preliminary report is not a cause finding. It is a first cut of the facts and a list of urgent safety points.

Airbus had already told investigators, in an earlier read of the digital flight-data recorder, that the three hydraulic systems went down for about four seconds and that key control surfaces were briefly unusable. The post-flight report logged low pressure on green, then blue and yellow, autopilot disconnect, faults on both elevators, and low reservoir levels on the yellow and blue sides. Those lines match the timeline AAIB has now put on paper.

Triple hydraulic loss on an A320 is not in the normal failure set pilots train every six months. Green, blue and yellow are designed to fail separately. When they fail together, the aircraft is a poorly damped tube at eight miles up. The fact that the systems recovered in seconds is why the flight continued to Delhi instead of diverting to the nearest runway. The fact that 24 people were injured is why the event is an accident, not an incident.

The drug-test finding will dominate the public argument. It should not erase the hydraulics. AAIB has asked DGCA to deal with the captain. The bureau still has to explain why three independent hydraulic circuits lost pressure in four seconds and why two reservoirs read low after landing. Those questions point at maintenance, fluid, pumps, sensors and software as much as at the man in the left seat.

AI 2379 departed Phuket at 01:41 UTC. At 03:40 UTC Kolkata control climbed it from 34,000 to 36,000 feet. The failure came 22 minutes later. Cabin damage was extensive enough to be listed in the report. Four of the injured were listed as serious. Names have not been released.

Indian carriers have spent two years under a sharper DGCA after a separate Air India disaster in 2025. This preliminary report lands in that climate. The regulator now has a written recommendation to act on a pilot who tested non-negative and a technical puzzle that the manufacturer has already described as a brief total hydraulic loss. Both files have to move at once.

The final report will take months. Until then the public record is the 10-page preliminary: three systems down, autopilot off, stall horn for two seconds, 664 feet of altitude swing, 24 injured, one failed drug test, no declared cause. That is enough for DGCA to move on the crew. It is not yet enough to say why an A320 at cruise lost all three hydraulics at the same time.