Cenvat credit eligibility denied for CVD on imported aircraft; ineligible credit does not become eligible after service tax levy. Credit of CVD on an imported aircraft is not allowable where the aircraft was used exclusively in providing exempted services at the time of import; under the Cenvat Credit Rules, credit on capital goods used only for exempted services is disallowed and such ab initio ineligible credit does not become eligible merely because the activity is later taxed.