Narrative:

About 7 hours of a 9 hour flight from paris to st louis had elapsed when I got out of my seat to stretch. The assigned relief pilot replaced me at that time and I stepped toward the rear of the cockpit, about 4 ft aft of the pilots. Both pilots were on headsets and turned to me saying that they had been requested to fly an 'offset' track 5 mi west of our current track. They wanted to confirm the FMC entry as this function is seldom used. I leaned forward and confirmed that an R5 entry was correct and I further cautioned that upon execution, an immediate 45 degree intercept would occur. Both pilots agreed that this is what was wanted and they proceeded. Not long after, I noticed that we were beginning a hard left turn to the south using the heading select mode of the autoplt. I asked what was happening and the pilots said center had given us this new turn to avoid a possible conflict. I could tell that there was some confusion and I returned to my seat. It was apparent that another aircraft was also on vectors and we were soon given a frequency change to the next center (chicago, I believe). The new controller asked us to explain what had transpired and my first officer explained that they had received, read back and the previous center had acknowledged a 5 mi 'offset' to the west. The new controller indicated that there must have been a communications breakdown and we should have been issued instruction to 'offset' 5 mi left (east). This entire episode was a bit disturbing to me as I tried to sort out and piece together the controller's comment with that which I heard from my crew and that which I observed while standing behind them. After some thought, I believe a controller should issue specific heading instructions to begin diverging tracks for traffic avoidance. Once divergence is established, further vectors or amended clrncs could be issued (i.e., '...maintain this heading to intercept...). We must also get some standardization in communications. The words west and left are obviously similar and apparently easily misunderstood. Controllers should also be aware of the 45 degree intercept/escape function in the program for offsets as found on the widebody transport. In lieu of vectors, this is what is executed. Center said something along the lines of 'no problem' when I returned to my seat, but I felt obligated to report this to NASA as a possible area of concern.

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Original NASA ASRS Text

Title: ACR GIVEN OFFSET TRACK, 5 MI W. ACKNOWLEDGED WITH READBACK. LATER GIVEN NEW TURN TO AVOID CONFLICT. ON HDOF QUESTIONED. MISCOM.

Narrative: ABOUT 7 HRS OF A 9 HR FLT FROM PARIS TO ST LOUIS HAD ELAPSED WHEN I GOT OUT OF MY SEAT TO STRETCH. THE ASSIGNED RELIEF PLT REPLACED ME AT THAT TIME AND I STEPPED TOWARD THE REAR OF THE COCKPIT, ABOUT 4 FT AFT OF THE PLTS. BOTH PLTS WERE ON HEADSETS AND TURNED TO ME SAYING THAT THEY HAD BEEN REQUESTED TO FLY AN 'OFFSET' TRACK 5 MI W OF OUR CURRENT TRACK. THEY WANTED TO CONFIRM THE FMC ENTRY AS THIS FUNCTION IS SELDOM USED. I LEANED FORWARD AND CONFIRMED THAT AN R5 ENTRY WAS CORRECT AND I FURTHER CAUTIONED THAT UPON EXECUTION, AN IMMEDIATE 45 DEG INTERCEPT WOULD OCCUR. BOTH PLTS AGREED THAT THIS IS WHAT WAS WANTED AND THEY PROCEEDED. NOT LONG AFTER, I NOTICED THAT WE WERE BEGINNING A HARD L TURN TO THE S USING THE HDG SELECT MODE OF THE AUTOPLT. I ASKED WHAT WAS HAPPENING AND THE PLTS SAID CENTER HAD GIVEN US THIS NEW TURN TO AVOID A POSSIBLE CONFLICT. I COULD TELL THAT THERE WAS SOME CONFUSION AND I RETURNED TO MY SEAT. IT WAS APPARENT THAT ANOTHER ACFT WAS ALSO ON VECTORS AND WE WERE SOON GIVEN A FREQ CHANGE TO THE NEXT CENTER (CHICAGO, I BELIEVE). THE NEW CTLR ASKED US TO EXPLAIN WHAT HAD TRANSPIRED AND MY FO EXPLAINED THAT THEY HAD RECEIVED, READ BACK AND THE PREVIOUS CENTER HAD ACKNOWLEDGED A 5 MI 'OFFSET' TO THE W. THE NEW CTLR INDICATED THAT THERE MUST HAVE BEEN A COMS BREAKDOWN AND WE SHOULD HAVE BEEN ISSUED INSTRUCTION TO 'OFFSET' 5 MI L (E). THIS ENTIRE EPISODE WAS A BIT DISTURBING TO ME AS I TRIED TO SORT OUT AND PIECE TOGETHER THE CTLR'S COMMENT WITH THAT WHICH I HEARD FROM MY CREW AND THAT WHICH I OBSERVED WHILE STANDING BEHIND THEM. AFTER SOME THOUGHT, I BELIEVE A CTLR SHOULD ISSUE SPECIFIC HDG INSTRUCTIONS TO BEGIN DIVERGING TRACKS FOR TFC AVOIDANCE. ONCE DIVERGENCE IS ESTABLISHED, FURTHER VECTORS OR AMENDED CLRNCS COULD BE ISSUED (I.E., '...MAINTAIN THIS HDG TO INTERCEPT...). WE MUST ALSO GET SOME STANDARDIZATION IN COMS. THE WORDS W AND L ARE OBVIOUSLY SIMILAR AND APPARENTLY EASILY MISUNDERSTOOD. CTLRS SHOULD ALSO BE AWARE OF THE 45 DEG INTERCEPT/ESCAPE FUNCTION IN THE PROGRAM FOR OFFSETS AS FOUND ON THE WDB. IN LIEU OF VECTORS, THIS IS WHAT IS EXECUTED. CENTER SAID SOMETHING ALONG THE LINES OF 'NO PROBLEM' WHEN I RETURNED TO MY SEAT, BUT I FELT OBLIGATED TO RPT THIS TO NASA AS A POSSIBLE AREA OF CONCERN.

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.