Just to clarify about the airworthiness certificat
Post# of 41413
This is separate from the certification process, as the FAA's airworthiness certificate basically says "This is a B742 and we have approved this design." The conformity evaluation is the FAA saying "We approve this aircraft to fly passengers or cargo in scheduled service operations." Every aircraft in Part 135 and Part 121 service undergoes a conformity evaluation. When Delta adds a new type of plane to their fleet, you guessed it, C-Check. In summation, the airworthiness certificate only allows the plane to be flown, whereas the conformity check allows the plane to be flown for commercial purposes by a commercial operator.
Hope I made sense there!
And a reference that will make it as clear as mud:
http://fsims.faa.gov/PICDetail.aspx?docId=890...,Ch16,Sec1