FLC OF ACR WDB ACFT DEV FROM ASSIGNED ALT WHEN THEY MISUNDERSTOOD AN EXPECTED CLRNC FOR AN ACTUAL ONE THROUGH THE HF RADIO FREQ.

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FLT XXX; AN FTR; WAS OPERATING BTWN NRT AND SIN. THE AIRWAY BEING USED WAS R471 BTWN HCN AND NOBOK INTXNS. THE INFRACTION BEING RPTED OCCURRED AFTER PASSING KADET INTXN SWBOUND ENRTE TO THE GUPIL INTXN. RADIO COMS WERE BEING CONDUCTED ON HF FREQ 3942 P AND 98903 S WITH MANILA AS THE CTLING AGENCY. OUR FLT HAD REQUESTED FL350 IN THE APPROX AREA OF HCN VOR FROM TAIPEI CTL. OUR REQUEST WAS DENIED AT THAT TIME FOR REASONS UNKNOWN. AFTER PASSING KADET INTXN; AN AREA WHERE ALT CHANGES ARE NORMALLY NOT ALLOWED; WE RECEIVED A CLRNC FROM MANILA TO CLB TO FL350. ALL 3 PLTS INITIALLY; EVEN THOUGH SEVERE STATIC AND OTHER AGENCIES SUCH AS SINGAPORE; HONG KONG; HO CHI MINH; BANGKOK AND VIENTIANE CAUSED CONSIDERABLE FREQ CONGESTION; WERE ABLE TO MAKE OUT WHAT WE ALL FELT WAS A CLRNC TO FL350. THE COPLT WAS FLYING AT THE TIME AND LEFT FL310 FOR FL350. AS WE LEFT 310; I BEGAN TO EXPRESS DOUBTS AS TO THE VALIDITY OF THE CLRNC AND REQUESTED THE COPLT TO IMMEDIATELY RETURN TO FL310. HE DID SO AFTER REACHING A HIGH ALT OF FL325. MANY XMISSIONS WERE REQUIRED TO REACH MANILA TO GET THE PROPER CLRNC AND TO ADVISE THEM OF THE FACT THAT WE WERE MAINTAINING FL310. THE CORRECT CLRNC WAS AN ADVISORY TO EXPECT FL350 AFTER PASSING NOBOK INTXN. NO TFC CONFLICT WAS INVOLVED IN THIS INCIDENT. THE REASON IT OCCURRED WAS BECAUSE TREMENDOUS OVER USE OF A SINGLE FREQ OVER THE S CHINA SEA. THIS TYPE OF FREQ OVER USE IS A POTENTIAL SAFETY PROB AND SHOULD BE CORRECTED IMMEDIATELY. HF RADIOS WITH THEIR STATIC PROBS ARE DIFFICULT ENOUGH AS AN OPERATIONAL PROB BUT TO HAVE THE MULTIPLE AGENCIES ALL CUTTING EACH OTHER OUT ALL THE TIME COMPOUNDS THE SIT. THE USE OF ADDITIONAL HF FREQ OVER THE S CHINA SEA IS GREATLY NEEDED.