DC10 crew missed a position estimated by 5 mins on the hawaiian tracks from the mainland.

Attributes
ACN	533914
Time
Date	200112
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : dopps
Altitude	msl single value : 34000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	DC-10 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other other
Flight Phase	cruise : level
Route In Use	enroute : pacific enroute airway : k576.airway
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp pilot : multi engine
Experience	flight time last 90 days : 200 flight time total : 13750 flight time type : 500
ASRS Report	533914
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	non adherence : published procedure non adherence : far non adherence : company policies other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : gps other flight crewa other flight crewb
Resolutory Action	none taken : anomaly accepted
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

When making our duets position report while flying wbound on the delta track between los angeles and honolulu, we estimated dopps (the next required position report) at XA02Z based on the displayed data of our #1 GPS system. For a period of about a half hour in the vicinity of doner (the next waypoint after duets) we encountered moderate clear air turbulence accompanied by rapid increases and decreases in mach speed, which required several power adjustments. Just prior to reaching and reporting dopps we noticed that the #1 GPS was now estimating dopps at XA07Z, a variance of 5 mins. Upon checking we realized that the #1 GPS, which was being used for position reporting, had either dropped or had never properly received, the forecast winds aloft data which had been inputted into the #2 GPS and transmitted to the #1. Apparently the #1 GPS had been estimating fixes using its own spot wind calculations instead of forecast winds. This combined with the loss of airspeed during encounters of turbulence probably caused the inaccurate estimate. Closer xchking between GPS system and better awareness of the effect of airspeed deviations on projected time estimates may have avoided this problem.

Original NASA ASRS Text

Title: DC10 CREW MISSED A POS ESTIMATED BY 5 MINS ON THE HAWAIIAN TRACKS FROM THE MAINLAND.

Narrative: WHEN MAKING OUR DUETS POS RPT WHILE FLYING WBOUND ON THE DELTA TRACK BTWN LOS ANGELES AND HONOLULU, WE ESTIMATED DOPPS (THE NEXT REQUIRED POS RPT) AT XA02Z BASED ON THE DISPLAYED DATA OF OUR #1 GPS SYS. FOR A PERIOD OF ABOUT A HALF HR IN THE VICINITY OF DONER (THE NEXT WAYPOINT AFTER DUETS) WE ENCOUNTERED MODERATE CLR AIR TURB ACCOMPANIED BY RAPID INCREASES AND DECREASES IN MACH SPD, WHICH REQUIRED SEVERAL PWR ADJUSTMENTS. JUST PRIOR TO REACHING AND RPTING DOPPS WE NOTICED THAT THE #1 GPS WAS NOW ESTIMATING DOPPS AT XA07Z, A VARIANCE OF 5 MINS. UPON CHKING WE REALIZED THAT THE #1 GPS, WHICH WAS BEING USED FOR POS RPTING, HAD EITHER DROPPED OR HAD NEVER PROPERLY RECEIVED, THE FORECAST WINDS ALOFT DATA WHICH HAD BEEN INPUTTED INTO THE #2 GPS AND XMITTED TO THE #1. APPARENTLY THE #1 GPS HAD BEEN ESTIMATING FIXES USING ITS OWN SPOT WIND CALCULATIONS INSTEAD OF FORECAST WINDS. THIS COMBINED WITH THE LOSS OF AIRSPD DURING ENCOUNTERS OF TURB PROBABLY CAUSED THE INACCURATE ESTIMATE. CLOSER XCHKING BTWN GPS SYS AND BETTER AWARENESS OF THE EFFECT OF AIRSPD DEVS ON PROJECTED TIME ESTIMATES MAY HAVE AVOIDED THIS PROB.

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.