The former air chief has been repeatedly questioned on the deal with UK-based helicopter maker AgustaWestland, in which kickbacks were allegedly paid to Indian officials and politicians to influence the contract for a dozen VVIP choppers for the President, Prime Minister and other top leaders of the country.

The CBI had registered a case against the former air chief and 18 others, including his cousins and European middlemen, three years ago.

Retired Air Marshal Tyagi, who headed the Air Force between 2004 and 2007, is accused by investigators in Italy and India of helping AgustaWestland win the chopper contract by tailoring specifications at the instance of his cousins.

Investigations have revealed that the Tyagis entered into a consultancy deal with middlemen in 2004, when Air Marshal Tyagi's cousins were certain that he would be the next air force chief and in a position to influence the deal.

Investigators say there is evidence that Air Mashal Tyagi met with a top official of Agusta's parent company Finmeccanica when he was Air Chief.

The specific allegation against the former air chief is that he reduced the required flying height for VVIP choppers from 6,000 m to 4,500 m, which helped AgustaWestland qualify.

Air Marshal Tyagi claimed that the change of specifications was a collective decision involving many departments.

The Enforcement Directorate alleges that payments were made through Tunisia-registered companies controlled by Switzerland-based intermediaries Guido Haschke and Carlo Gerosa and transferred to accounts in India and Mauritius.

Three helicopters had been delivered to India before the deal was stalled in 2013.