Air India flight 2379, an Airbus A320 flying from Phuket to Delhi, suddenly lost altitude on 4 August, injuring 20 passengers and four crew members. The cause remains unclear: investigators are examining whether a hydraulic-system malfunction, pilot actions or both were responsible.
Mint examines what is known and what investigators are looking for.
What does Airbus’s preliminary report say?
At about 04:02:44 GMT, the aircraft recorded low pressure in its Green hydraulic system, one of three that power the flight controls. Within about a second, Blue and Yellow were also temporarily affected, depriving the aircraft of hydraulic power. The report says the flight-control surfaces were unresponsive for about four seconds.
At 04:02:46, Autopilot 2 disconnected. The aircraft then pitched up and lost altitude. The hydraulic systems recovered shortly after—Blue first, followed by Yellow and Green—and the flight-control surfaces became responsive again.
Airbus’s data establishes the sequence, but not what caused the simultaneous pressure loss. To be sure, Airbus hasn't commented on the report yet.
Is this a concern for Airbus?
It is a serious event, but too early to say whether it points to a wider A320-family problem. The aircraft is central to India’s fleet: IndiGo and Air India operate more than 400 A320-family aircraft, while a substantial part of their combined order book of about 900 aircraft is with Airbus.
The A320 has three hydraulic systems to provide backup if one fails. What makes this incident unusual is that all three appeared to be affected within seconds.
Executives aware of the discussions said Airbus has asked Air India to test the hydraulic systems, pressure switches and pressure transducers, which measure hydraulic pressure and tell the aircraft’s computers whether it is normal. Investigators are examining whether there was a genuine pressure loss, a problem with the measuring equipment or another underlying fault.
A two-member Airbus team is in India, and checks on the aircraft, now parked at Delhi airport, are underway.
What is the investigation for?
Investigators will reconstruct the incident using flight-data and cockpit voice recorders, examine the aircraft’s maintenance history and test its hydraulic systems, pressure switches and transducers.
Airbus has also called for checks of leak-measurement switches, which detect hydraulic leakage, and associated wiring to establish why the hydraulic systems registered low pressure.
The pilots’ conduct and decision-making will also come under scrutiny, particularly their actions after the hydraulic systems were affected. The Aircraft Accident Investigation Bureau (AAIB) is leading the investigation, with technical assistance from Airbus and France’s Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA).
Could the pilot’s condition have caused the technical problem?
A positive drug test does not explain a hydraulic-pressure failure. Airbus’s data shows that the technical problem occurred independently of the pilots’ corrective actions.
One of India’s two pilot associations has said the pilot-in-command and co-pilot followed the “rulebook to the T” to ensure a safe landing, and that the pilot’s positive test and the aircraft’s technical fault are separate issues.
The pilot’s condition could, however, be relevant to how the emergency was handled.
A positive test shows that a psychoactive substance, or its markers, was detected in the pilot’s body. It does not by itself establish impairment at that moment.
The pilot, in his response to the Directorate General of Civil Aviation (DGCA), said he was taking sleep medication.
The investigation therefore needs to establish three things: Was the substance present? Was the pilot impaired? And, if so, did that affect his response? One question being examined, for instance, is why the pilots continued to Delhi rather than landing at nearby Kolkata.
What changes could follow in India’s aviation sector?
Airbus has recommended detailed checks of the hydraulic systems and pressure-monitoring components. The findings will determine whether any component needs repair or replacement, or whether wider inspections of other A320s are warranted.
Air India has ordered screening of all its pilots for prohibited substances, going beyond its existing testing arrangements. It remains to be seen whether the rules will be tightened more broadly.
The two responses address different risks: the technical investigation seeks to establish why the aircraft temporarily lost control of its flight surfaces and prevent a recurrence, while pilot testing seeks to ensure crews are free from prohibited substances.
The final investigation will establish whether the two issues were unrelated or combined to make the incident more serious.
How do other countries approach pilot drug and alcohol testing?
The US has formal employer-run drug and alcohol testing programmes, with the Federal Aviation Administration specifying minimum annual random-testing rates and requiring employers or medical review officers to report verified positive results. For 2026, the rates for covered safety-sensitive aviation employees are 25% for drugs and 10% for alcohol.
Australia also uses random and no-notice testing for people performing safety-sensitive aviation activities.
In the UK, the Civil Aviation Authority requires drug and alcohol screening as part of the initial Class 1 medical examination for commercial pilots. Random psychoactive-substance screening can also be conducted during renewal or revalidation when warranted by a risk assessment.