Exclusive: Under scanner — tech snag hours before Ahmedabad Air India plane crash, if switch can cut off without pilot command

The Stabilizer Position Transducer is essentially a sensor that controls aircraft pitch — the up and down movement of the nose — and transmits the data in electrical signals to the flight control system to ensure that responses to pilot input are accurate. The official said the malfunction was checked and the engineer did the trouble shooting as per Boeing procedure.

“The malfunction is a critical issue as it can trigger incorrect responses in flight control, including unintended fuel cut-off signal,” the official said. But he added, “The Stabilizer Position Transducer malfunction did not cause this crash, but the question is whether it led to multiple sensor failure.”

A few weeks before, there were at least two more incidents, one of electrical snags in the aircraft that led to flight cancellation and another relating to false fuel system warning flashing on the screen of the aircraft. The official said the flight data analysis would focus on the “trail of errors” as noted in technical logs to ascertain the health of the electric and software components of the aircraft.

According to him, the aircraft had previously experienced two major snags, including a flight cancellation due to an “unresolvable electric snag” in December 2024 and an emergency landing in 2015 due to Cabin Air Compressor (CAC) surge, a known malfunction on Boeing 787-8 Dreamliner. “On December 12, 2024, incidentally, the same AI-171 scheduled flight from Ahmedabad to Gatwick could not take off as it experienced a massive technical snag that led Air India to abort boarding… The issue was an electrical failure that had been indicated in the incoming flight from Delhi. The flight took off the next day on December 13 after the issue was resolved… A day prior, it had made a round trip between Delhi and Zurich, and no snags were reported,” he said.

Families of victims of the Air India plane crash at the DNA testing centre in Ahmedabad. (Express Photo: Bhupendra Rana)

The investigators would delve into the ‘history of technical fault’ or malfunction in the course of the aircraft’s life, the official said.

On July 12, a preliminary report by the Aircraft Accident Investigation Bureau (AAIB), an office attached to the Ministry of Civil Aviation, had brought much attention to a cockpit exchange between the two pilots of the ill-fated Boeing Dreamliner 787-8 over the “transition” of the fuel control switches that allow and cut fuel to the plane’s engines. “In the cockpit voice recording, one of the pilots is heard asking the other why did he cut-off. The other pilot responded that he did not do so,” the report said, without identifying the pilots or any other part of the conversation.

Queries sent to the Director General of AAIB, Directorate General of Civil Aviation and Air India, did not elicit a response.

The official also said that the Engine Indication and Crew Alerting System (EICAS) of the aircraft in some flights preceding the June 12 Ahmedabad-Gatwick flight had displayed some system warnings. On at least two occasions in the preceding three weeks, technical logs have recorded warnings, including a fuel system malfunction that later turned out to be a false alarm, the official said.

“The AI-171 pilots had performed the functions of take-off, consistent with the protocols, right from a pulled back yoke to the flap handle assembly, thrust levers as seen in the wreckage… the aircraft lifted off to initiate the climb after reaching Vr speed when the sensors switched to the ‘air’ mode. Whether electric failure or software bug led to un-commanded actions and resulted in an engine failure within seconds, causing a loud bang, deployment of the RAT and the transition of the fuel switches to cut-off mode… given the sensor snag reported in the prior flight, we cannot overlook the possibility of a system error that resulted in the unexplained transition,” the official said.

“The probe is on to ascertain if the switch locks were disengaged due to an anomaly or if the FADEC’s (Full Authority Digital Engine Control) Engine Control Unit (the brain of the aircraft) malfunctioned as the microprocessor could have misinterpreted the commands and initiated uncontrolled actions,” he said.

The Flight Data Recorder, according to officials, captures electrical signals and not physical position of the gear inside the flight. “It does not give any picture of where the controls were positioned, but only captures what the sensors and back systems did,” the official said.

“Usually, FADEC will attempt auto relight but it cannot do so without fuel supply… So, record shows that the pilots desperately attempted to cycle the fuel switch back to the run mode even as RAT began generating power… this was done to attempt relighting and thrust recovery. Unfortunately, with no safe altitude available, it could not be achieved… We have not come across any alarming or adverse medical report concerning any of the two pilots,” the official said.

The Indian Express has reported earlier how if the aircraft had achieved an elevation of 3,600-4,900 feet, it could have made a safe Mayday landing with the power generated by the RAT. In this case, the AI-171 had gained an altitude of only 625 feet.

The probe agency is also corroborating the sequence of events with the statement of the lone witness in the case — Viswashkumar Ramesh, the surviving passenger on Seat 11A, who described the 40-second flight as having been “stalled right after take-off following a loud bang”, “flickering green and white cabin lights turning on” and a feeling of the pilots “giving race” to attempt thrust before the plane crashed on to the ground.