Narrative:

At FL390 unable to maintain assigned cruise speed. Requested permission from ATC through shannon to turn north to parallel track 30 NM and descend to FL370 in order to pick up desired speed. We were unable to make prompt contact using HF radio. When speed started to drop below vref+80 we turned right until 30 NM north of course and started a descent to FL376, picked up speed and returned to FL390, then returned to track by 58N 20W. Cancelled prior request to ATC. Continued on track. 1) new (to the aircraft) first officer flying. 2) flight plan called for +6 temperature when in fact we experienced +10 at level off, then increased to +12. 3) normally use VNAV for all climbs above 10000'. For some reason we used vertical speed (no speed protection) for the climb. This is part of the reason our speed feel to vref+80. 4) ca was distracted while he gave position report at 58N 10W and the first officer allowed the speed to go from 12 KTS above vref+80 to 4 KTS below vref+80. At level off VNAV was engaged and cruise power was not enough power to maintain speed. Constant power was engaged. We were unable to regain speed until descent was started, then speed came back to mach.80. Supplemental information from acn 160125: the aircraft was cleared by ATC to cross 58N 010 west at FL390 and mach.80, and then follow a westbound north atlantic track. FL390 was at the aircraft performance limit, given its gross weight at the time. Due to warmer than forecast temperatures at FL390 and non-optimum climb speeds used, the aircraft crossed 58N 010W at FL390, but at a slowly decreasing airspeed. In spite of maximum continuous power being used, the aircraft continued to decelerate slowly in level flight. After regaining the proper mach # of .80, the aircraft was climbed back to FL390 and the assigned track was rejoined. No conflict with other aircraft was known to have occurred. This even highlights the archaic nature of communications and ATC over the north atlantic. When an aircraft experiences difficulties, it is often impossible to obtain altered clrncs via high frequency relay stations. This is due to congestion on the frequencys used, random dead spots in high frequency coverage, and the time delay involved in forwarding clearance requests to ATC via relay station and obtaining a reply. It is unfortunate that the air transport industry, so technologically advanced in many areas, is unable at the present time to avail itself of satellite relay devices in order to provide transponder and VHF voice communications directly with ATC. Such a direct link would have probably precluded the need for the deviation that took place.

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Original NASA ASRS Text

Title: ACR WDB TAKEN OFF NAT TRACK FOR DESCENT ACCOUNT UNABLE TO MAINTAIN AIRSPEED AT FL390.

Narrative: AT FL390 UNABLE TO MAINTAIN ASSIGNED CRUISE SPD. REQUESTED PERMISSION FROM ATC THROUGH SHANNON TO TURN N TO PARALLEL TRACK 30 NM AND DSND TO FL370 IN ORDER TO PICK UP DESIRED SPD. WE WERE UNABLE TO MAKE PROMPT CONTACT USING HF RADIO. WHEN SPD STARTED TO DROP BELOW VREF+80 WE TURNED RIGHT UNTIL 30 NM N OF COURSE AND STARTED A DSNT TO FL376, PICKED UP SPD AND RETURNED TO FL390, THEN RETURNED TO TRACK BY 58N 20W. CANCELLED PRIOR REQUEST TO ATC. CONTINUED ON TRACK. 1) NEW (TO THE ACFT) F/O FLYING. 2) FLT PLAN CALLED FOR +6 TEMP WHEN IN FACT WE EXPERIENCED +10 AT LEVEL OFF, THEN INCREASED TO +12. 3) NORMALLY USE VNAV FOR ALL CLBS ABOVE 10000'. FOR SOME REASON WE USED VERT SPD (NO SPD PROTECTION) FOR THE CLB. THIS IS PART OF THE REASON OUR SPD FEEL TO VREF+80. 4) CA WAS DISTRACTED WHILE HE GAVE POS RPT AT 58N 10W AND THE F/O ALLOWED THE SPD TO GO FROM 12 KTS ABOVE VREF+80 TO 4 KTS BELOW VREF+80. AT LEVEL OFF VNAV WAS ENGAGED AND CRUISE PWR WAS NOT ENOUGH PWR TO MAINTAIN SPD. CONSTANT PWR WAS ENGAGED. WE WERE UNABLE TO REGAIN SPD UNTIL DSNT WAS STARTED, THEN SPD CAME BACK TO MACH.80. SUPPLEMENTAL INFO FROM ACN 160125: THE ACFT WAS CLRED BY ATC TO CROSS 58N 010 W AT FL390 AND MACH.80, AND THEN FOLLOW A WBND N ATLANTIC TRACK. FL390 WAS AT THE ACFT PERFORMANCE LIMIT, GIVEN ITS GROSS WT AT THE TIME. DUE TO WARMER THAN FORECAST TEMPS AT FL390 AND NON-OPTIMUM CLB SPDS USED, THE ACFT CROSSED 58N 010W AT FL390, BUT AT A SLOWLY DECREASING AIRSPD. IN SPITE OF MAX CONTINUOUS PWR BEING USED, THE ACFT CONTINUED TO DECELERATE SLOWLY IN LEVEL FLT. AFTER REGAINING THE PROPER MACH # OF .80, THE ACFT WAS CLBED BACK TO FL390 AND THE ASSIGNED TRACK WAS REJOINED. NO CONFLICT WITH OTHER ACFT WAS KNOWN TO HAVE OCCURRED. THIS EVEN HIGHLIGHTS THE ARCHAIC NATURE OF COMS AND ATC OVER THE N ATLANTIC. WHEN AN ACFT EXPERIENCES DIFFICULTIES, IT IS OFTEN IMPOSSIBLE TO OBTAIN ALTERED CLRNCS VIA HIGH FREQ RELAY STATIONS. THIS IS DUE TO CONGESTION ON THE FREQS USED, RANDOM DEAD SPOTS IN HIGH FREQ COVERAGE, AND THE TIME DELAY INVOLVED IN FORWARDING CLRNC REQUESTS TO ATC VIA RELAY STATION AND OBTAINING A REPLY. IT IS UNFORTUNATE THAT THE AIR TRANSPORT INDUSTRY, SO TECHNOLOGICALLY ADVANCED IN MANY AREAS, IS UNABLE AT THE PRESENT TIME TO AVAIL ITSELF OF SATELLITE RELAY DEVICES IN ORDER TO PROVIDE XPONDER AND VHF VOICE COMS DIRECTLY WITH ATC. SUCH A DIRECT LINK WOULD HAVE PROBABLY PRECLUDED THE NEED FOR THE DEVIATION THAT TOOK PLACE.

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.