MANGALORE - Indian investigators recovered Tuesday the "black box" flight recorder they hope will unlock the mystery surrounding the crash of an Air India Express plane that killed 158 people.

The discovery followed a three-day search that began hours after the Boeing 737-800, flying from Dubai to the southern Indian city of Mangalore, overshot the runway, plunged into a gorge and burst into flames.

"It's intact," an official from the Directorate General for Civil Aviation (DGCA) said as he held up the battered recorder for media gathered at the hilltop crash site.

The Civil Aviation Ministry said the black box contained "the most vital source of information" about Saturday's crash.

"Though apparently impacted by the crash, it will be subjected to further tests for decoding and made available to the investigators," the ministry said in a statement.

Only eight people among the 166 passengers and crew survived Saturday's crash.

The cause of the disaster has been the subject of intense speculation, given the good flying conditions and visibility at the time and the fact that there was no communication from the cockpit to suggest a technical problem.

Indian officials have declined to comment on what might have gone wrong, although Civil Aviation Minister Praful Patel said Monday that pilot error "could not be ruled out".

He stressed, however, that the chief pilot was "very experienced," having logged more than 10,000 hours of flying time.

Some eyewitness reports have suggested a fault with the landing trajectory, while other reports have pointed to a possible tyre burst and an attempt by the pilot to take off again after touchdown.

The cockpit voice recorder, which tracks communications between the pilots and with the air traffic controllers, was recovered late Sunday.

But it is the black box, which records every flight parameter from take-off to landing, that investigators believe holds the key to what went wrong.

The Bajpe airport that serves Mangalore presents particular challenges to pilots.

Its "table-top" runway, which is shorter than at other airports, is surrounded by a steep valley on all sides, making an overshoot particularly hazardous.

It was India's first major air crash since 2000 and its worst aviation disaster since 1996 when two jets collided mid-air over New Delhi, killing nearly 350 people.

The Air India Express plane, belonging to a budget airline operated by the state-run carrier, broke into several pieces as it careered off the runway and plunged into a steep, forested valley.

The passengers who survived miraculously managed to escape the broken fuselage before it was engulfed in the flames that made the subsequent task of removing the badly charred bodies a gruesome ordeal for the rescue teams.

All 158 bodies were eventually recovered, but 22 were so badly disfigured that they can only be identified through DNA testing -- prolonging the agony for grieving families waiting to claim their loved ones.

The black box will be sent to New Delhi where a senior DGCA official said it would take several weeks to decode the data and compare it with information gleaned from the cockpit voice recorder.

"We hope to go through that and understand what happened," the official told AFP.

The digital flight data acquisition unit, which is similar to the black box but stores information over a shorter period of time, has also been recovered.

The 160 passengers -- all of them Indian nationals -- included 137 adults, 19 children and four infants.

Most were migrant workers returning from the Gulf where many Indians from Karnataka and other southern states find low-paid employment in cities such as Dubai as construction workers or domestic staff.

They send much of their earnings back to India as remittances, and return to home for their annual leave. - Maktoob