Did technical snag prompt ‘uncommanded’ action of fuel switches in Air India flight?

Amid the ongoing probe in the Air India 171 crash on June 12, speculations are rife about a technical snag that could have prompted an “uncommanded” action in the fuel switch module. This comes as the investigation is trying to ascertain the events that led up to the crash. The transition of the fuel switch from ‘run’ to ‘cutoff’ is a focal point of the investigation.

According to a report in The Indian Express, investigators are closely studying snags that cropped up in the electrical and software components of the aircraft that could have triggered ‘uncommanded’ actions. In fact, a pilot who had flown the same plane before it took off from Ahmedabad, leading to its crash, had flagged a Stabiliser Position Transducer malfunction in the technical log. The official said that the snag was looked into and addressed as per the instructions in the Boeing manual.

WHAT IS THE STABILISER POSITION TRANSDUCER?

The Stabiliser Position Transducer is a sensor that controls the movement – the ups and downs of the nose of the plane. It transmits the data in electrical signals to the flight control system that ensures the responses to pilot input are accurate.

The official told the daily that the malfunction is a critical issue and it can trigger incorrect responses in flight control, including “unintended fuel cut-off signal”.

The Stabiliser Position Transducer defect could not have led to the crash but it could have led to multiple sensor failure, the official said.

THE COCKPIT CLUE

The Aircraft Accident Investigation Bureau (AAIB) report identified the conversation between the pilots as soon as the fuel was cut off. According to the cockpit voice recordings, one of the pilots asked, “Why did you cut off?” After that, the other replied, “I didn’t.”

However the report did not clarify which pilot asked what.

Meanwhile, a report in Wall Street Journal, quoting sources aware of the US officials’ investigation, said that it was the first officer who asked the senior captain why he had cut the fuel off. To that, the senior captain responded that he hadn’t.

FUEL SWITCH ISSUES?

According to a report in NDTV, an Air India official said that the carrier has completed precautionary inspections of the locking mechanism of the fuel control switch (FCS) in all of its Boeing 787-8 aircraft and found no issues. The engineering team carried out inspection of the modules in its planes over the weekend but found nothing.

The Air India team had also undergone a throttle control module (TCM) – which includes the FCS — replacement as per the Boeing maintenance schedule.

Before this, the FCS of the entire Boeing 737 Max fleet of Air India Express was also checked but nothing was found, said the official.