CBI sources said while Air Marshal (Retd) Gujral has been asked to appear for questioning tomorrow, Tyagi will be examined on Monday.
Both have been questioned at length in 2013 but the fresh round of questioning was necessitated after April 7 order of an Italian court.
The Milan Court of Appeals--equivalent of Indian high courts--has given details of how alleged bribes were paid by helicopter maker Finmeccanica and AgustaWestland to Indian officials through middlemen to clinch the deal.
CBI which has received a copy of the Milan court order has now prepared a fresh set of questionnaire on the basis of the decision to put to Tyagi and Gujral.
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Tyagi has denied allegations against him and has claimed that the decision to reduce the ceiling was taken by a group of senior officials including Gujral, CBI has so far maintained that Gujral was questioned as a witness but remain tightlipped if he will still retain the same status.
CBI had registered a case against Tyagi along with 13 others including his cousins and European middlemen in the case.
However, this decision was taken in consultation with the officials of SPG and the Prime Minister's Office including the then NSA M K Narayanan.
CBI has alleged reduction of the service ceiling--maximum height at which a helicopter can perform normally--allowed the UK-based firm to get into the fray as, otherwise, its helicopters were not even qualified for submission of bids.
The agency had already questioned several bureaucrats including former cabinet secretary B K Chaturvedi and Comptroller and Auditor General Shashikant Sharma who was the then Defence Secretary, the then SPG chiefB V Wanchoo and Narayanan who were all allegedly party to the decision to reduce the ceiling was allegedly finalised in 2005.