Heading track position deviation. Navigation error.

Attributes
ACN	242612
Time
Date	199305
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : pit
State Reference	PA
Altitude	msl bound lower : 8000 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : takeoff climbout : intermediate altitude ground : preflight
Route In Use	enroute airway : pit
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : commercial pilot : flight engineer pilot : instrument pilot : atp
Experience	flight time last 90 days : 200 flight time total : 19000 flight time type : 2000
ASRS Report	242612
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

There was no data base coordinates for gate X at pit. The FMC gave the airport, which was about 2400 ft off from IRS (IRU's) last known position after parking at gate. Since it appeared closer than airport, I selected last known position. Somehow or other, when inserted into FMC it was off. After takeoff we were told to intercept a radial off ewc VOR. Where it was on our glass tube was about 5-10 mi east of where it actually was. ATC at pit gave us vector. The left IRU had history of trouble and had been replaced. History of slow update. Using maps and FMC at terminal is not practical. One believes FMC? No answer for this one.

Original NASA ASRS Text

Title: HDG TRACK POS DEV. NAV ERROR.

Narrative: THERE WAS NO DATA BASE COORDINATES FOR GATE X AT PIT. THE FMC GAVE THE ARPT, WHICH WAS ABOUT 2400 FT OFF FROM IRS (IRU'S) LAST KNOWN POS AFTER PARKING AT GATE. SINCE IT APPEARED CLOSER THAN ARPT, I SELECTED LAST KNOWN POS. SOMEHOW OR OTHER, WHEN INSERTED INTO FMC IT WAS OFF. AFTER TKOF WE WERE TOLD TO INTERCEPT A RADIAL OFF EWC VOR. WHERE IT WAS ON OUR GLASS TUBE WAS ABOUT 5-10 MI E OF WHERE IT ACTUALLY WAS. ATC AT PIT GAVE US VECTOR. THE L IRU HAD HISTORY OF TROUBLE AND HAD BEEN REPLACED. HISTORY OF SLOW UPDATE. USING MAPS AND FMC AT TERMINAL IS NOT PRACTICAL. ONE BELIEVES FMC? NO ANSWER FOR THIS ONE.

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.