FLC OF A BRITISH HAWKER HS125-700 (HS25) CLBED FROM ASSIGNED ALT DURING CRUISE ON AN OCEANIC AIRWAY AFTER REACHING THEIR FLT PLAN FIX FOR AN ALT CHANGE AND NOT BEEN ABLE TO CONTACT CTR AFTER SEVERAL ATTEMPTS. AFTER FINALLY CONTACTING THE CTR THEY WERE ASSIGNED BACK TO THEIR PREVIOUSLY ASSIGNED ALT.

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PROB AROSE DUE TO LOSS OF COM AT FL370 NEAR THE LACKI INTXN ON A300. WE WERE IN A NON RADAR HF RADIO ONLY ENVIRONMENT. CLRNC WAS GIVEN AT THE DEP ARPT AS 'AS FILED.' OUR FILED RTE HAD A CLB FROM FL370 TO FL390 AT THE LACKI INTXN. UPON REACHING LACKI; CONTACT WAS ATTEMPTED ON MULTIPLE FREQS ALONG WITH GUARD WITH NO SUCCESS. FLT CONDITIONS AFFECTED THE DECISION TO CLB (MODERATE TURB AND IN AND OUT OF CLOUD TOPS) AFTER CONTINUOUS ATTEMPTS; THE DECISION TO CLB WAS MADE TO THE CLRED ALT OF FL390. CONTACT WAS FINALLY MADE AT HUBER INTXN AT XY23Z WHEREUPON NEW YORK RADIO GAVE US AN IMMEDIATE DSCNT TO FL370 WHICH WAS PROMPTLY COMPLIED WITH. WHILE CONTACT WAS LOST; WE MAINTAINED A CONSTANT VISUAL SEARCH FOR OTHER ACFT; WHICH HAD NOT BEEN POSSIBLE AT FL370 DUE TO FLT CONDITIONS. THERE ARE 3 ITEMS WHICH COULD CREATE A SOLUTION TO THE PROB. FIRST; A FULL RTE CLRNC SHOULD BE GIVEN ANY TIME AN ACFT WILL BE OPERATING OUTSIDE OF A RADAR ENVIRONMENT WHERE COMS MIGHT BE BLOCKED; INCLUDING ALL ALT CHANGES. THIS WOULD HAVE CLRNC ON TAPE ALONG WITH ALTS. SECOND; MORE REQUIRED RPTING POINTS WITH BETTER LONG RANGE COM OVER ATLANTIC RTES. WITH MORE RPTING POINTS; ERRORS ON SIDES WOULD BE FOUND EARLIER. THIRDLY; IF IN THE RADIO POS RPT THE NEXT FIX AND THE EXPECTED FLT LEVEL AT THE NEXT FIX WOULD CATCH ANY DISCREPANCIES BEFORE THEY OCCUR.