Narrative:

During 3 hour and 20 min flight, approximately midpoint, air carrier X checked in with manila control passing marda intersection and gave standard non-radar position report on HF to ATC. We were advised immediately by another us flag carrier. He was estimating same position, same altitude in 1 min, same direction of flight. Other aircraft was essentially no turn at the intersection. We made approximately 60 degree left turn. (Our routing bkk-tpe; other aircraft singapore-nrt.) we had climbed direct to FL370 leaving bkk, however this was initial contact with manila control. Both aircraft involved made repeated calls to manila, informing of conflict. Then we heard air carrier Y aircraft given clearance to descend to FL350, but no acknowledgement. We finally received clearance to climb to FL390 and departed FL370. It took 7-10 mins to get this clearance. Air carrier Y verified we were in sight. We never saw air carrier Y as it was behind us. I feel the problem was due to manila control, or possibly other flight had misunderstood assigned altitude assignment. HF communications with manila are extremely poor. They were blocked repeatedly or covered by bangkok, ho chi minh and other aircraft all using same H.F. Frequency. Supplemental information from acn 142251: air carrier X reported hong kong and manila, after which air carrier Y asked us (on HF) to verify FL370. We did so on 128.95. He then said he could see us (he only saw us after knowing exactly where to look 10-15 mi?). Manila was advised and tried, we thought, to get air carrier Y. To descend to FL350. After about 10 mins of communications so bad the descent clearance was unreliable, they (manila) tried to clear us, air carrier X, to FL390. After about 10 mins, we had pieced together enough to feel we could safely climb to FL390. The time to solve the problem was caused by unreliable communication on HF. Air carrier Y having visibility sep with air carrier X was safer than a climb not clearly received. Supplemental information from acn 142039: air carrier X bkk/tpe arwy routing bkk/tpe northeast dptp-selka/A1 btrn/vipop B460 marda R93 nobok. Flying at assigned altitude of 37000 ft air carrier X turned at marda intersection onto R93. Air carrier Y told us on HF that he also was at 37000 ft and 1 min behind us from lavon X. Manila was controling.

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Original NASA ASRS Text

Title: ACR Y HAD LESS THAN STANDARD SEPARATION FROM ACR X. SYSTEM ERROR.

Narrative: DURING 3 HR AND 20 MIN FLT, APPROX MIDPOINT, ACR X CHKED IN WITH MANILA CTL PASSING MARDA INTXN AND GAVE STANDARD NON-RADAR POS RPT ON HF TO ATC. WE WERE ADVISED IMMEDIATELY BY ANOTHER U.S. FLAG CARRIER. HE WAS ESTIMATING SAME POS, SAME ALT IN 1 MIN, SAME DIRECTION OF FLT. OTHER ACFT WAS ESSENTIALLY NO TURN AT THE INTXN. WE MADE APPROX 60 DEG L TURN. (OUR ROUTING BKK-TPE; OTHER ACFT SINGAPORE-NRT.) WE HAD CLBED DIRECT TO FL370 LEAVING BKK, HOWEVER THIS WAS INITIAL CONTACT WITH MANILA CTL. BOTH ACFT INVOLVED MADE REPEATED CALLS TO MANILA, INFORMING OF CONFLICT. THEN WE HEARD ACR Y ACFT GIVEN CLRNC TO DSND TO FL350, BUT NO ACKNOWLEDGEMENT. WE FINALLY RECEIVED CLRNC TO CLB TO FL390 AND DEPARTED FL370. IT TOOK 7-10 MINS TO GET THIS CLRNC. ACR Y VERIFIED WE WERE IN SIGHT. WE NEVER SAW ACR Y AS IT WAS BEHIND US. I FEEL THE PROB WAS DUE TO MANILA CTL, OR POSSIBLY OTHER FLT HAD MISUNDERSTOOD ASSIGNED ALT ASSIGNMENT. HF COMS WITH MANILA ARE EXTREMELY POOR. THEY WERE BLOCKED REPEATEDLY OR COVERED BY BANGKOK, HO CHI MINH AND OTHER ACFT ALL USING SAME H.F. FREQ. SUPPLEMENTAL INFO FROM ACN 142251: ACR X RPTED HONG KONG AND MANILA, AFTER WHICH ACR Y ASKED US (ON HF) TO VERIFY FL370. WE DID SO ON 128.95. HE THEN SAID HE COULD SEE US (HE ONLY SAW US AFTER KNOWING EXACTLY WHERE TO LOOK 10-15 MI?). MANILA WAS ADVISED AND TRIED, WE THOUGHT, TO GET ACR Y. TO DSND TO FL350. AFTER ABOUT 10 MINS OF COMS SO BAD THE DSNT CLRNC WAS UNRELIABLE, THEY (MANILA) TRIED TO CLR US, ACR X, TO FL390. AFTER ABOUT 10 MINS, WE HAD PIECED TOGETHER ENOUGH TO FEEL WE COULD SAFELY CLB TO FL390. THE TIME TO SOLVE THE PROB WAS CAUSED BY UNRELIABLE COM ON HF. ACR Y HAVING VIS SEP WITH ACR X WAS SAFER THAN A CLB NOT CLEARLY RECEIVED. SUPPLEMENTAL INFO FROM ACN 142039: ACR X BKK/TPE ARWY ROUTING BKK/TPE NE DPTP-SELKA/A1 BTRN/VIPOP B460 MARDA R93 NOBOK. FLYING AT ASSIGNED ALT OF 37000 FT ACR X TURNED AT MARDA INTXN ONTO R93. ACR Y TOLD US ON HF THAT HE ALSO WAS AT 37000 FT AND 1 MIN BEHIND US FROM LAVON X. MANILA WAS CTLING.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.