The 91-year-old father of the Air India pilot in a June crash that killed 260 has asked India's Supreme Court to order an independent investigation that takes into account causes other than pilot action, sources familiar with the matter said.

The lawsuit represents a major escalation of protests by the father and a pilots' union against the Indian government's handling of the world's worst aviation disaster in a decade, which came soon after takeoff in the western city of Ahmedabad.

The plea by the father, Pushkar Raj Sabharwal, for an investigation by a panel of aviation experts headed by a retired Supreme Court judge, comes weeks after he criticised the government investigation.

He said two officials from India's Aircraft Accident Investigation Bureau (AAIB) who visited him had implied that his son, Sumeet Sabharwal, cut the fuel to the plane’s engine after take-off.

The government has denied such accusations, calling the investigation "very clean" and "very thorough".

On October 11, the father told the court the investigation team appeared to "predominantly focus on the deceased pilots ... while failing to examine or eliminate other more plausible technical and procedural causes," said one of the sources who saw his filing.

It also asked for the government investigation to be closed and handed to a new panel headed by a retired Supreme Court judge that includes aviation experts, said the two sources, who spoke on condition of anonymity.

The judges have yet to take up the case, which the Supreme Court's website showed on Thursday had been filed jointly by the father and the Federation of Indian Pilots against the government, though it gave no details.

The AAIB, the civil aviation ministry, planemaker Boeing and Air India did not immediately respond to Reuters requests for comment. Sabharwal's father and the pilots' union did not respond to emails seeking comment.

A preliminary AAIB report showed the Boeing Dreamliner's fuel engine switches had almost simultaneously flipped from run to cutoff just after takeoff.

The cockpit recording of dialogue between the two pilots supported the view that Captain Sabharwal had cut the flow of fuel to the engines, a source briefed on U.S. officials' early assessment of evidence in July told Reuters.

The Federation of Indian Pilots has about 5,000 members.