Narrative:

On descent on dupont arrival STAR to phl we're told to expect holding at terri. Captain selected hold page on his CDU and entered all data and executes hold function. Autoplt is on with LNAV engaged. As we approach terri, I select hold page on my CDU verifying all data is entered correctly. The aircraft enters the hold at terri turning right (direct entry) to the outbnd leg. I monitor the performance of the LNAV in hold and upon its successful interception of the holding course inbound I begin reviewing the ILS 9R approach chart. The aircraft is in cloud with continuous light to moderate turbulence with intermittent rain. Upon completion of approach chart review I see aircraft not in a right turn to the outbnd leg but instead a left turn away from the hold which at time of discovery had progressed 40 degrees left of inbound course. I selected heading mode immediately right turn 30 degree bank to return to the hold. The controller at this time asked if we were aware terri required right turns and of our position. Holding at 210-220 KTS in turbulence, TAS is 250-260 KTS in addition to a very strong swind 60-65 KT tailwind component on the northerly inbound holding course a left 40 degree heading change followed by a right turn heading change of 180-200 degrees at ground speeds in the 300-320 KT range I'm sure resulted in a significant deviation out of protected holding airspace. I can't explain why a properly programmed hold function would turn left when programmed to turn right but to prevent a recurrence monitoring LNAV performance more carefully than normal during IMC when course changes occur.

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Original NASA ASRS Text

Title: FLT CREW IN MLG PROGRAMMED FMC FOR A R TURN HOLDING PATTERN. PROGRAMMING WAS DOUBLE CHECKED. ACFT ENTERED PROPER HOLDING PATTERN BUT ON SECOND LAP TURNED LEFT INSTEAD OF RIGHT AS PROGRAMMED. CTLR INTERVENED AND FLT CREW CORRECTED THE TRACK DEVIATION.

Narrative: ON DSNT ON DUPONT ARR STAR TO PHL WE'RE TOLD TO EXPECT HOLDING AT TERRI. CAPT SELECTED HOLD PAGE ON HIS CDU AND ENTERED ALL DATA AND EXECUTES HOLD FUNCTION. AUTOPLT IS ON WITH LNAV ENGAGED. AS WE APCH TERRI, I SELECT HOLD PAGE ON MY CDU VERIFYING ALL DATA IS ENTERED CORRECTLY. THE ACFT ENTERS THE HOLD AT TERRI TURNING R (DIRECT ENTRY) TO THE OUTBND LEG. I MONITOR THE PERFORMANCE OF THE LNAV IN HOLD AND UPON ITS SUCCESSFUL INTERCEPTION OF THE HOLDING COURSE INBND I BEGIN REVIEWING THE ILS 9R APCH CHART. THE ACFT IS IN CLOUD WITH CONTINUOUS LIGHT TO MODERATE TURB WITH INTERMITTENT RAIN. UPON COMPLETION OF APCH CHART REVIEW I SEE ACFT NOT IN A R TURN TO THE OUTBND LEG BUT INSTEAD A L TURN AWAY FROM THE HOLD WHICH AT TIME OF DISCOVERY HAD PROGRESSED 40 DEGS L OF INBND COURSE. I SELECTED HDG MODE IMMEDIATELY R TURN 30 DEG BANK TO RETURN TO THE HOLD. THE CTLR AT THIS TIME ASKED IF WE WERE AWARE TERRI REQUIRED R TURNS AND OF OUR POS. HOLDING AT 210-220 KTS IN TURB, TAS IS 250-260 KTS IN ADDITION TO A VERY STRONG SWIND 60-65 KT TAILWIND COMPONENT ON THE NORTHERLY INBND HOLDING COURSE A L 40 DEG HDG CHANGE FOLLOWED BY A R TURN HDG CHANGE OF 180-200 DEGS AT GND SPDS IN THE 300-320 KT RANGE I'M SURE RESULTED IN A SIGNIFICANT DEV OUT OF PROTECTED HOLDING AIRSPACE. I CAN'T EXPLAIN WHY A PROPERLY PROGRAMMED HOLD FUNCTION WOULD TURN L WHEN PROGRAMMED TO TURN R BUT TO PREVENT A RECURRENCE MONITORING LNAV PERFORMANCE MORE CAREFULLY THAN NORMAL DURING IMC WHEN COURSE CHANGES OCCUR.

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.