PAN-PAN call before Delhi adds new clue to AI altitude drop probe

Air India (AI) Phuket-Delhi flight that reportedly lost nearly 300 feet in altitude on August 4 reportedly sought priority handling from the Air Traffic Control (ATC) during the latter part of the journey and informed controllers that four to five passengers had suffered injuries.

"The pilot of Air India flight AI2379, operating from Phuket to Delhi, communicated the PAN-PAN alert after crossing Odisha airspace. He informed ATC that around four-five passengers had been injured and that the aircraft required landing assistance," a senior official associated with Delhi ATC said.

Following the communication, ATC alerted ambulance services and gave the aircraft priority handling for landing. The aircraft reportedly experienced a sudden drop in altitude while operating over Odisha. The circumstances surrounding the event, including whether the altitude change was linked to turbulence, a technical issue or another factor, remain under investigation.

Investigators are likely to examine the reported timeline of the communication closely, particularly in relation to the earlier altitude loss and the information available to the cockpit crew during the flight.

A PAN-PAN transmission is an internationally recognised aviation urgency signal used when an aircraft or people on board require urgent assistance, but the situation is not considered to involve the grave and imminent danger associated with a MAYDAY declaration.

In the case of AI2379, investigators are expected to establish why the urgency call was made only during the latter part of the flight if the aircraft had experienced a significant altitude change earlier.

The recorded communication with the ATC could also help establish what the pilots told controllers about the altitude loss, passenger injuries, aircraft systems and any other operational concerns. ATC radio recordings, along with the aircraft's cockpit voice recorder and flight-data recorder, are expected to provide investigators with a more complete chronology.

The precise wording of the transmission will be important. The available account does not, by itself, establish that the pilot intentionally withheld information from ATC or that the cockpit crew had a complete assessment of the situation at the time of the call.

The number of people injured in the incident has varied between preliminary accounts. Later reports have put the figure at 24 passengers and crew members, while earlier figures cited by the airline were lower. Investigators are therefore expected to rely on hospital and medical records, airport documentation and other official material to establish the final number and nature of the injuries.

Information cited in reports has referred to warnings involving hydraulic systems, flight controls and other aircraft components, including low-pressure indications and low-fluid warnings in two hydraulic reservoirs.

There have also been reports of autopilot disconnects and indications concerning elevator-control systems. However, the presence of individual warnings does not automatically establish that the aircraft suffered a complete hydraulic or flight-control failure. The investigation will have to determine whether the indications were connected to the altitude loss and whether any technical malfunction contributed to the episode.

The Airbus A320 family relies on multiple hydraulic systems to provide redundancy for several critical functions, including flight controls, landing gear and braking.

Another issue under discussion is the decision to continue to Delhi rather than divert to the nearest suitable airport. Captain Sam Thomas, President of the Airline Pilots Association of India (ALPA India), said the decision to divert depends on the overall circumstances and is not determined solely by the captain.

"MAYDAY is used for grave or impending danger, such as when an aircraft is not under control, has a structural issue or fire. If the aircraft is flyable but there is another urgent issue, such as a medical emergency, PAN-PAN is the correct call," Thomas said.

"We believe the captain made the right decision to come to Delhi, which offered better logistical support for the injured passengers," he said. He said the decision regarding the destination airport is taken after considering inputs from the co-pilot, cabin crew and the airline.

The Aircraft Accident Investigation Bureau has taken custody of the aircraft's Flight Data Recorder and Cockpit Voice Recorder as part of the probe. Airbus and French aviation investigation authorities are also assisting with the technical examination.

The cockpit crew has also faced scrutiny over reports concerning the captain's post-flight drug screening. Reports have said an initial screening produced a positive result and that subsequent confirmatory testing also indicated marijuana use. Both pilots were reportedly removed from flying duties pending the inquiry.

Separate reports have raised questions about the captain's sleep, medication and overall fitness for duty. Investigators will have to establish the relevance, if any, of these factors to the incident rather than treating them as evidence of causation.