The incident - in which 127 people died - has been described as one of the worst disasters in Russian military history.

A Russian court found 27-year-old Doku Dzhantemirov "guilty of planning and carrying out an act of terror".

Four others suspected of involvement in the attack are still at large.

Prosecutors said Dzhantemirov helped set up the portable missile launcher used to bring down the helicopter as it prepared to land at the Russian military base in Khankala, near the Chechen capital, Grozny.

The court in the southern Russian city of Rostov-on-Don also convicted him of videotaping the helicopter's downing

According to Russia's Interfax news agency, Dzhantemirov was also ordered to pay 100,000 rubles ($3,500) to the relatives of each victim and 50,000 rubles ($1,720) to each of the surviving victims.

Military under fire

The attack on the helicopter led to serious criticism of the Russian military.

Mi-26 Heavy lifting transport helicopter Introduced 1983 Can carry more than 80 troops and equipment Maximum speed 295 km/h Russia's airborne cow

According to official documents, the Mi-26, equipped to carry 80 troops, was loaded with at least 140 people.

The Russian military was using the helicopter to ferry troops in Chechnya despite a 1997 order prohibiting such actions.

President Vladimir Putin criticised the Russian Defence Ministry for the violation and an official inquiry was launched.