The US National Transportation Safety Board (NTSB) officials joined US Federal Aviation Administration officials in Ahmedabad, in western India's Gujarat state, to survey the crash site, a source with direct knowledge said.
The Boeing 787-8 Dreamliner with 242 people on board, bound for Gatwick Airport south of London, began losing height seconds after take-off in Ahmedabad on Thursday, and erupted in a huge fireball as it hit buildings below.
All but one on board were declared dead in the world's worst aviation disaster in a decade.
About 30 people died on the ground.
Air India and the Indian government were looking at several aspects of the crash, including issues linked to its engine thrust, flaps, and why the landing gear remained open as the plane took off and then came down.
US Department of Transportation Secretary Sean Duffy said on Friday he was in the process of deploying a team from the aviation administration and the safety board to India.
Boeing and GE, whose engines were used in the plane, were also sending teams.
"We'll take action should any recommendations come forward from the NTSB's investigation," Duffy said.
The aviation administration and the safety board did not immediately respond to Reuters' queries outside regular business hours.
The aviation administration has said India will lead the investigation, but the safety board is the official US representative for assisting, while the administration provides technical support.
Boeing officials will also look at various parameters, including the angle of landing.
About 10 officials were present at the site on Sunday, including those from the safety board, the source said.
India's aviation regulator has ordered all Boeing 787s being operated by local carriers to be inspected.
The crash brings a fresh challenge for both Air India, which has for years been trying to revamp its fleet, and Boeing, which is trying to rebuild public trust following a series of safety and production crises.
In Ahmedabad, doctors were struggling to identify bodies that were charred in the incident, resorting to dental samples and DNA profiling.
DNA samples of 32 victims from the crash have been successfully matched, Rajnish Patel, additional superintendent at the city's main hospital, said on Sunday.
"The bodies for which DNA samples have been matched are being handed over to the families with due respect," he said.
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