US aviation experts have been sent to India to join the investigation.
Philip Crowley, a US state department spokesman, said: "India's Directorate General for Civil Aviation has requested technical assistance.
"An eight-member team of investigators from the United States National Transportation Safety Board, the Federal Aviation Administration and Boeing will arrive in Mangalore on Tuesday to participate in the investigation."
All 158 bodies have been recovered but DNA tests are being conducted to determine the identities of 12 passengers.
At a news conference in New Delhi on Monday, Manmohan Singh, India's prime minister, expressed his "deep condolences" to the families of those who died and held a one-minute silence.
Air crash investigators from India's Directorate General of Civil Aviation (DGCA) have inspected the airport runway and are studying tapes of air traffic control contact with the plane in its final moments.
The DGCA said in a statement that the cockpit voice recorder (CVR) "is expected to yield the desired information" even though it has been affected by fire.
Aircraft manufacturer Boeing said it was sending a team to help the investigation.
'No distress call'
Survivors of India's worst air crash since nearly 350 people were killed when two planes collided in mid-air over New Delhi in 1996 described hearing a loud thud shortly after touchdown at the hill-top Bajpe airport.
|Indian officials said landing conditions at time of the crash were fair [Reuters]
Landing conditions were fair with good visibility, officials said, and there had been no distress call from the cockpit.
Praful Patel, the civil aviation minister, described the chief pilot, a British national of Serbian origin, as a "very experienced" flier who had logged 10,000 hours of flying time.
On Saturday, Patel said that the sanded safety area surrounding the runway in the event of an overshoot was shorter than at some airports.
Air India Express is a budget airline operated as a subsidiary by the state-run carrier.
Many of the passengers were migrant workers returning from jobs in the Gulf to visit their families.
India's last major plane crash was in 2000, when 61 people were killed after a passenger jet plunged into a residential area near the eastern city of Patna.
The country's air safety record has been good in recent years despite the rapid increase in airlines keen to serve increasingly wealthy domestic customers.