The agency, in its charge sheet filed before a special CBI court last month, has alleged that in a meeting on April 1, 2005, attended by the then defence secretary, the operational requirement of the VVIP helicopters was decided to be of "twin engines".
The CBI has alleged that during the meeting there was no suggestion for any amendment in the requirements that the helicopters "should be twin engined".
It has alleged that helicopters having more than twin engines and one engine were not eligible for the bids.
"However, by adding the word 'at least' before 'twin engined' the helicopter EH-101 (subsequently known as AW-101) was dishonestly and fraudulently made eligible to participate in the bids with the approval of Air Chief Marshal S P Tyagi," the CBI has alleged.
The changes were made without assigning any reason, the agency alleged.
"As per the directions of Air Marshal (Retd) J S Gujral, Air Cmde M Matheswaran added the word 'at least' before the words 'twin engined'...," the CBI alleged in the charge sheet.
Gujral discussed these revised requirements with the then air chief S P Tyagi and Vice Chief S K Malik and obtained "oral approval" of Tyagi, it claimed.
He gave a note that the "above (matter) was discussed" during PSOs conference, the CBI said.
"Investigation has established that Air Marshal J S Gujral has taken false plea that the revised ORs (operational requirements) were to be thoroughly discussed and to be put up accordingly," it said.
It is amply clear that the word "at least" was inserted by Air Commodore M Matheswaran on the instructions of Air Marshal J S Gujral in furtherance of the criminal conspiracy with other persons in order to favour and accommodate EH-101 for participating in the bidding process, it alleged.
"Investigation has revealed that the exact copy of the said revised ORs approved by the Chief of Air Staff on April 13, 2005, has been recovered by Swiss Police from the house of Haschke's (one of the European middlemen) mother during search. The same has been received in the execution report of LR from Italian authority," it said.
LRs are Letters Rogatory or judicial request in which investigation agency of one country requests agency of another country to conduct probe in their jurisdiction. These requests are routed through the court of one country to another.
The agency has alleged that there was an estimated loss of 398.21 million euros (approximately Rs 2,666 crore) to the exchequer in the deal that was signed on February 8, 2010, for the supply of VVIP choppers worth 556.262 million euros.
Seventy-two-year old Tyagi is the first chief of the IAF to be chargesheeted in a corruption or a criminal case by the CBI.
Others named in the charge sheet are -- Gujral, Tyagi's cousin Sanjeev alias Julie, advocate Gautam Khaitan, alleged European middlemen Carlo Gerosa, Christian Michel, Guido Haschke, former AgustaWestland CEO Bruno Spagnolini and former Finmeccanica Chairman Giuseppe Orsi.
They have been chargesheeted for offences under the Prevention of Corruption Act and the IPC in the case relating to alleged bribery of Rs 450 crore.