An MD80 flight crew experienced a navigation error departing dfw on the NOBLY3 approaching navye. An...

Narrative:

Departing dfw on the NOBLY3 at 1000 ft the egpws system said 'terrain terrain too low' and we dismissed this as an anomaly. The autopilot was on tracking to navye; both displays were showing that we had about two miles to go to navye when ATC said turn left to a heading 080. She asked what departure we were on and then what do you show? My response was the NOBLY3 navye and then I read the next three fixes. ATC said that we were two miles south of navye. We said that our display showed that we were two miles north of navye. My first officer and I discussed what could have possibly gone wrong. The navigation data dates were correct; the departure runway was correct; and there were no discontinuities the route. We informed ATC that our RNAV was inoperative and continued the flight. Upon arriving I called ATC departure control; and expressed that we could not figure out what had gone wrong. All of the inputs into the FMS were correct and that the autopilot was on. His response was that we would follow it up with a report. I then called maintenance control. He said that the 1000 ft terrain terrain to low was a sign the FMS did not know were it was. We did a report to maintenance explaining what had happened then we crew placarded the FMS and the egpws.

Original NASA ASRS Text

Title: An MD80 flight crew experienced a navigation error departing DFW on the NOBLY3 approaching NAVYE. An IRS malfunction was suspected as the cause; although all systems appear to be normal.

Narrative: Departing DFW on the NOBLY3 at 1000 FT the EGPWS system said 'terrain terrain too low' and we dismissed this as an anomaly. The autopilot was on tracking to NAVYE; both displays were showing that we had about two miles to go to NAVYE when ATC said turn left to a heading 080. She asked what departure we were on and then what do you show? My response was the NOBLY3 NAVYE and then I read the next three fixes. ATC said that we were two miles south of NAVYE. We said that our display showed that we were two miles north of NAVYE. My First Officer and I discussed what could have possibly gone wrong. The NAV data dates were correct; the departure runway was correct; and there were no discontinuities the route. We informed ATC that our RNAV was inoperative and continued the flight. Upon arriving I called ATC Departure Control; and expressed that we could not figure out what had gone wrong. All of the inputs into the FMS were correct and that the autopilot was on. His response was that we would follow it up with a report. I then called Maintenance Control. He said that the 1000 FT terrain terrain to low was a sign the FMS did not know were it was. We did a report to maintenance explaining what had happened then we crew placarded the FMS and the EGPWS.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	844033
Time
Date	200907
Local Time Of Day	1201-1800
Place
Locale Reference	D10.TRACON
State Reference	TX
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Climb Initial Climb
Route In Use	SID NOBLY3
Flight Plan	IFR
Component
Aircraft Component	INS / IRS / IRU
Person 1
Function	Captain Pilot Not Flying
Person 2
Function	First Officer Pilot Flying
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance Deviation - Track / Heading All Types

An MD80 flight crew experienced a navigation error departing dfw on the NOBLY3 approaching navye. An IRS malfunction was suspected as the cause; although all systems appear to be normal.