More than two days after an Air India Express passenger airliner crashed while landing at Mangalore airport in the southern Indian state of Karnataka, mystery still shrouds over what actually led to the early morning accident which claimed the lives of 158 people.

Though initial probe has indicated "human error", investigators are trying to unravel the mystery behind the crash of the ill- fated plane on Saturday by finding answers to questions like what could have possibly gone wrong or did the pilot of the Air India Express IX 812 attempt a last-minute take off after the flight overshot the runway.

Aviation sources claimed that the throttle in the cockpit, extricated from the debris, was found in a forward position and this clearly suggested the pilot may have attempted a final thrust to take-off seconds before the crash.

"We are considering all kinds of theories behind the crash," the sources said.

Investigators are going through the Cockpit Voice Recorder (CVR) and the Digital Flight Data Acquisition Unit (DFDAU) -- collectively called Black Box -- which record cockpit conversation and technical details, from the wreckage of the ill-fated Air India Express. But the search for the crucial Digital Flight Data Recorder (DFDR), also part of Black Box, still continues.

While the CVR records radio transmissions and sounds in the cockpit such as the pilot's conversation with the Air Traffic Controller, the DFDR logs actual flight conditions, including altitude, airspeed, heading, vertical acceleration and aircraft pitch. DFDAU records short-duration flight parameters.

"The recovered Black Box was today brought to the accident lab of the Director General of Civil Aviation in the national capital where it will be opened and to find out what exactly went wrong. But, it will take at least two weeks to analyze the data," the sources said.

Experts from the plane's manufacturer Boeing are also going to help in deciphering the flight data recorder, the sources said.

The Air India Express plane, a budget carrier of the country's national carrier, crashed after overshooting as it attempted to land at the Mangalore airport's hilltop runway, and exploded into a fiery wreckage Saturday, killing 158 people in what is being claimed as one of India's worst aviation disasters in 14 years. Eight passengers miraculously survived the crash.