New Delhi : The CBI has begun a probe into an alleged scam of Rs 487 crore related to the over-valuation of inferior quality coal imported from Indonesia, and passed on to the BSE-traded NTPC Ltd and to Arvali Power Corporation (APC) as superior quality coal, in collusion with officials. The action of the agency follows a Directorate of Revenue Intelligence (DRI) investigation that has highlighted over-invoicing in imports between 2011-12 and 2014- 15, officials said on Tuesday. The CBI FIR is against Ahmed A R Buhari, promoter of Coastal Energy Private Limited (CEPL), Chennai and unidentified officials of NTPC Ltd, Metals and Minerals Trading Corporation (MMTC), Aravali Power Company Pvt Ltd (APC). The agency booked them under the charges of criminal conspiracy cheating and provisions of the Prevention of Corruption Act, the officials said. According to the modus operandi noted in the FIR, NTPC and APC had floated global tenders for the supply of imported coal of a certain grade and quality. The grade and quality of the coal are crucial for achieving certain levels of power plant operations. MMTC and Chennai-based CEPL, emerged successful bidders for the supply of coal. CEPL instead of importing coal from Indonesia directly, routed their supply through Dubai-based sister concerns, enabling them to manipulate invoices and quality certification, reports the PTI.