C414 DEVELOPED ENG PROBLEMS DURING CRUISE. EMER WAS DECLARED AND THE FLT RECEIVED PRIORITY HANDLING TO DEST.

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WHILE CRUISING AT FL180 ENRTE TO ZZZ ON A FERRY FLT; IT WAS NOTED THAT THE MANIFOLD PRESSURE ON THE R ENG BEGAN TO FLUCTUATE +/-2 INCHES; ACCOMPANIED BY INTERMITTENT SURGING OF THE R ENG. THE FLUCTUATION CONTINUED FOR A PERIOD OF TIME UNTIL IT WAS DETERMINED THAT THIS FLUCTUATION MAY CAUSE THE LOSS OF THE L ENG. WE ATTEMPTED TO TROUBLESHOOT THE PROB BY ISOLATING THE FERRY FUEL SYS FROM THE ACFT FUEL SYS; BUT NO CHANGE WAS NOTED. WHEN IT BECAME APPARENT THAT CORRECTING THE PROB WAS NOT POSSIBLE; COMMERCIAL RADIO WAS NOTIFIED AND AN EMER WAS DECLARED. THE COMPANY REP CONTACTED US THROUGH AN HF PATCH AND ALSO HELPED TO TRY AND TROUBLESHOOT THE PROB. THE COMPANY REP ADVISED US TO TRY AND DSND. WE WERE CLRED TO 16000 FT; AND UPON REACHING; ENG SURGING SMOOTHED OUT; BUT THE FLUCTUATIONS REMAINED UNCHANGED. WE TOLD COMMERCIAL RADIO THAT OUR INTENTIONS WERE TO PROCEED DIRECT ZZZ AND LAND; AND ALSO ACCEPTED THE OFFER OF A MIL ESCORT. APPROX 400 MI WSW OF ZZZ COMMERCIAL RADIO ADVISED US THAT ATC HAD A RERTE AROUND MIL ACTIVITY THAT WOULD LEAD US ABOUT 80 MI FROM OUR COURSE. THE PIC DETERMINED THAT THIS RTE WOULD PUT THE FLT IN JEOPARDY DUE TO OUR FUEL STATE; AND ALSO IF THE ENG WERE TO BECOME INOP; WOULD MAKE A DITCHING UNAVOIDABLE. HE REMINDED COMMERCIAL RADIO THAT WE HAD DECLARED AN EMER SEVERAL HRS EARLIER AND THE URGENCY OF THE SITUATION HAD NOT CHANGED; AND WE NEEDED TO PROCEED DIRECT TO ZZZ. AFTER SEVERAL MINS; COMMERCIAL RADIO ADVISED THAT ATC HAD CLRED US DIRECT TO ZZZ AND THAT THE MIL ACTIVITY WAS NO LONGER ACTIVE. WE PROCEEDED DIRECT TO ZZZ WITH NO EVENT AND LANDED SAFELY. I BELIEVE THAT BY CONDUCTING FURTHER FLT TESTING PRIOR TO THE CONDUCTING TRANSOCEANIC FERRY FLT; AND EVAL OF ALL REALMS OF FLT THAT WILL BE ENCOUNTERED DURING THE XING; WOULD HELP TO BRING ATTN TO ANY PROBS THAT MAY ARISE DURING THE OP. ALL FERRY FLTS SHOULD BE REQUIRED TO CONDUCT TEST FLTS PRIOR TO THEIR FERRY. WHILE IN THIS CASE A TEST FLT WAS ALLOWED; IN OTHER CASES; FERRY PERMITS HAVE BEEN ISSUED WITHOUT TEST FLTS ALLOWED BY THE OPERATING LIMITATIONS OF THE SPECIAL FLT PERMIT. THIS WOULD ALLOW THE OPERATOR TO FIND PROBS THAT COULD CAUSE A SAFETY HAZARD DURING THE XING. BY REQUIRING SUCH FLTS; THIS WOULD REDUCE THE RISK OF A FAILURE OR MALFUNCTION THAT MAY TURN INTO AN EMER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE DURATION OF THIS FLT WAS APPROXIMATELY 13 1/2 HRS. ACFT MODIFICATIONS ARE NECESSARY TO COMPLETE THESE FLTS. HF RADIOS ARE INSTALLED; THE ENG OIL SYSTEM IS MODIFIED; AND ADDITIONAL FUEL TANKS ARE REQUIRED FOR THE FLTS; RESULTING IN AN OVERWEIGHT CONDITION. THE REPORTER STATED THAT IN SOME INSTANCES A TEST FLT IS FLOWN TO ENSURE THAT ALL THESE SYSTEMS OPERATE NORMALLY; BUT IN MANY CASES THIS IS NOT ACCOMPLISHED PRIOR TO THE ISSUANCE OF A FERRY PERMIT. THE REPORTER WOULD PREFER THAT A TEST FLT IS ACCOMPLISHED PRIOR TO EVERY FERRY FLT.