The families of four passengers who died on an Air India jet that crashed in June have filed a lawsuit in the US against planemaker, Boeing, and aircraft parts maker, Honeywell, accusing the companies of negligence.

The lawsuit filed Tuesday, and seen by the BBC, said faulty fuel switches caused the accident and accused the companies of doing "nothing" despite being aware of the risks of the aircraft's design.

Air India Flight 171 bound for London Gatwick, a Boeing 787, crashed shortly after takeoff from Ahmedabad, killing 260 people.

Fuel switches have become a focus for investigators after a preliminary inquiry found that fuel to the engines was cut off moments after the plane left the ground.

The US Federal Aviation Administration (FAA) has said earlier that fuel control switches in Boeing aeroplanes are safe.

The BBC has contacted Boeing and Honeywell for a response.

The US plane manufacturer did not comment on the case. Instead it pointed to India's Aircraft Accident Investigation Bureau's (AAIB) preliminary investigation report into the crash.

The lawsuit alleges that both firms knew about the risk of a crash since they developed and marketed the 787 Dreamliner and its components.

It cited a 2018 FAA advisory that urged - but did not mandate - operators to inspect the fuel switches' locking mechanism to ensure that it could not be accidentally moved, thereby cutting off fuel supply.

In the case of Air India Flight 171, the switch was moved from "run" to the "cut-off" position, hampering the thrust of the plane, according to the AAIB's preliminary investigation report.

The families said this amounted to a design "defect" that "allowed for inadvertent cutoff of fuel supply and total loss of thrust necessary to propel" the plane.

They said: "And what did Honeywell and Boeing do to prevent the inevitable catastrophe? Nothing."

The companies also failed to warn airlines that the switches required inspection and repair, and did not supply replacement parts to enable its customers to install them, according to the lawsuit.

Boeing and Honeywell "sat idly" behind a gentle advisory that merely recommended inspecting the switches, said the families, who are represented by Texas-based Lanier Law Firm.

A more detailed report of the crash is expected sometime in 2026.

A total of 229 passengers, 12 cabin crew and 19 people on the ground perished when the plane crashed. (BBC)

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