FLT CREW OF SA227 ACCUSED BY FAA RAMP INSPECTORS OF OPERATING IN VIOLATION OF ACFT OPS CERTIFICATE.

Narrative

UPON COMPLETION OF A PART 91 FLT TO KSOS; WE WERE MET ON THE RAMP BY 3 FAA INSPECTORS. THE INSPECTORS CONDUCTED A CHK OF OUR ACFT; DOCUMENTS; AND CERTIFICATES. WE WERE ASKED WHAT TYPE OF OP WE WERE OPERATING UNDER. WE REPLIED 'PART 91.' MAINT RELATED ITEMS WERE POINTED OUT ON THE ACFT; BUT NO TAGS WERE ISSUED. WE WERE TOLD BY THE FAA THAT WE COULD TAKE CARE OF THE ITEMS UPON RETURN TO DEST. WE WERE TOLD BY THE FAA THAT 'SPECIFIC ACCUSATIONS' HAD BEEN MADE AGAINST US CONCERNING THE OP OF OUR ACFT UNDER PART 135. THE ACFT WAS NOT AIRWORTHY; HOWEVER; THIS ACFT IS NOT ON A 135 CHARTER CERTIFICATE. WE FLEW THE ACFT AT THE DIRECTION OF THE OWNERS. WHEN WE ARRIVED AT OUR HOTEL; WE CALLED THE OWNER OF THE ACFT. AFTER SOME INVESTIGATION; WE FOUND THAT WE (THE PLTS) MAY HAVE FLOWN THE PLANE UNDER SOMETHING OTHER THAN PART 91. UPON OUR RETURN TO OUR DEST; THE FAA WAS AGAIN WAITING FOR US. WE WERE INSPECTED AGAIN; AND WE WERE ASKED 'WHY DID YOU FLY THE ACFT WITH THE WRITE-UPS GIVEN TO YOU BY THE FAA IN KSUS; WITHOUT A FERRY PERMIT?' WE TOLD HIM THE KSUS FAA SAID IT WAS 'OK. THE WRITE-UPS ARE NOT AIRWORTHINESS MATTERS.' MUST PLTS VERIFY HOW AN OWNER IS UTILIZING HIS ACFT? CAN THE FAA BE A LITTLE MORE STANDARDIZED? I (WE) DON'T WANT TO LOSE OUR CERTIFICATES FOR THIS.