CBI on Monday questioned ex-IAF chief SP Tyagi in connection with alleged corruption in the Rs 3,600-crore in AgustaWestland VVIP chopper deal.
The agency had issued him summons on Friday.
CBI had registered a case against Tyagi along with 13 others and European middlemen in the case.
Former air chief has been accused of reducing flying ceiling of the helicopter from 6,000m to 4,500m (15,000ft) so that AgustaWestland was included in the bids.
However, this decision was reportedly taken in consultation with the officials of SPG and the Prime Minister's Office.
The investigating agency had quizzed former IAF Deputy Chief JS Gujral on Saturday in the case.
Both, Tyagi and Gujral were questioned at length in 2013 but the fresh round of questioning was necessitated after recent order of an Italian Court which indicated corruption in the deal.
The court has given details of how alleged bribes were paid by helicopter maker Finmeccanica and AgustaWestland to Indian officials through middlemen to clinch the deal.
AgustaWestland's Rs 3,600 crore contract for supplying 12 VVIP choppers to the Indian Air Force was scrapped by the former UPA government over charges of paying kickbacks to Indian agents.
In January 2013, India cancelled the deal and the CBI was assigned to investigate the matter.