Embraer captain experiences a track deviation departing dfw on the nelyn 3 departure. A slight discr...

Narrative:

After completing the climb checklist; the first officer (pilot monitoring) pointed out that the two FMS's were not aligned and that hers showed us left of course. Given that information; I failed to tell TRACON that we were unsure of the accuracy of our navigation instruments. First officer monitored the #2 FMS and emphasized that it was continuing to show off course; with the course deviating to the east. Just at the point that I was going to heading mode to turn in a more westerly direction and let ATC know that we were concerned about our navigation instruments; the controller gave us a turn to the west and told us we had been .10 off course and then drifted to approximately .20 off course to the east. The responsibility for this deviation rests solely with me. I was given excellent information by the first officer and failed to act upon it when it was first offered. I do not know why the course diverged from that of the nelyn 3 departure course. Q parameters were met and both FMS's were GPS. If there is a .1 variation in course deviation on an RNAV departure (or arrival) immediately ask ATC for heading information as navigation capabilities are suspect.

Original NASA ASRS Text

Title: Embraer Captain experiences a track deviation departing DFW on the NELYN 3 departure. A slight discrepancy existed between the Captain's and First Officer's display with the First Officer's apparently correct; according to ATC.

Narrative: After completing the climb checklist; the First Officer (Pilot Monitoring) pointed out that the two FMS's were not aligned and that hers showed us left of course. Given that information; I failed to tell TRACON that we were unsure of the accuracy of our navigation instruments. First Officer monitored the #2 FMS and emphasized that it was continuing to show off course; with the course deviating to the east. Just at the point that I was going to heading mode to turn in a more westerly direction and let ATC know that we were concerned about our navigation instruments; the Controller gave us a turn to the west and told us we had been .10 off course and then drifted to approximately .20 off course to the east. The responsibility for this deviation rests solely with me. I was given excellent information by the First Officer and failed to act upon it when it was first offered. I do not know why the course diverged from that of the NELYN 3 departure course. Q parameters were met and both FMS's were GPS. If there is a .1 variation in course deviation on an RNAV departure (or arrival) immediately ask ATC for heading information as navigation capabilities are suspect.

Data retrieved from NASA's ASRS site as of July 2013 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	1069269
Time
Date	201302
Local Time Of Day	0601-1200
Place
Locale Reference	DFW.Airport
State Reference	TX
Aircraft 1
Make Model Name	EMB ERJ 145 ER/LR
Operating Under FAR Part	Part 121
Route In Use	SID NELYN 3
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types

Embraer captain experiences a track deviation departing dfw on the nelyn 3 departure. A slight discrepancy existed between the captain's and first officer's display with the first officer's apparently correct; according to ATC.