Air carrier first officer reported that a course disparity between ATC and cockpit indications while...

Narrative:

We were taking off from 26L out of atlanta. At 600 feet ca called for the auto pilot on. It was engaged and we started flying the departure. We made the turn towards mpass. Tower called and asked if we were direct mpass and from all of our indications in the flight deck; we were. Later departure asked us the same thing; if we were direct mpass. We told him yes we were; every indication from our flight instruments indicated we were direct mpass. Departure came back and told us we were a little north of course. We responded with we were on the departure and going direct to mpass; we had no indications saying otherwise. Departure told us later that they were doing some GPS testing and that might be the cause of the northerly course. Captain had put the flight plan into the FMS. We did a clearance verification procedure that verified our flight plan. Everything looked normal and correct. I personally went through the legs page and verified each leg from the departure and afterwards to our destination. Everything was correct. Taxing down to the runway we did our before takeoff checklist which we verified for the second time that we were doing the correct departure with the first fix mpass. Three times we verified our route and first fix. I honestly think it had something to do with GPS testing that departure later told us they were doing.

Original NASA ASRS Text

Title: Air carrier First Officer reported that a course disparity between ATC and cockpit indications while departing ATL was apparently due to GPS testing.

Narrative: We were taking off from 26L out of Atlanta. At 600 feet CA called for the Auto Pilot on. It was engaged and we started flying the departure. We made the turn towards MPASS. Tower called and asked if we were direct MPASS and from all of our indications in the flight deck; we were. Later Departure asked us the same thing; if we were direct MPASS. We told him yes we were; every indication from our flight instruments indicated we were direct MPASS. Departure came back and told us we were a little north of course. We responded with we were on the departure and going direct to MPASS; we had no indications saying otherwise. Departure told us later that they were doing some GPS testing and that might be the cause of the northerly course. Captain had put the flight plan into the FMS. We did a clearance verification procedure that verified our flight plan. Everything looked normal and correct. I personally went through the legs page and verified each leg from the departure and afterwards to our destination. Everything was correct. Taxing down to the runway we did our Before Takeoff checklist which we verified for the second time that we were doing the correct departure with the first fix MPASS. Three times we verified our route and first fix. I honestly think it had something to do with GPS testing that Departure later told us they were doing.

Data retrieved from NASA's ASRS site 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	1480377
Time
Date	201709
Local Time Of Day	0601-1200
Place
Locale Reference	ATL.Airport
State Reference	GA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Medium Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	GPS & Other Satellite Navigation
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	ATC Issue All Types Deviation - Procedural Clearance Deviation - Track / Heading All Types

Air carrier first officer reported that a course disparity between ATC and cockpit indications while departing atl was apparently due to GPS testing.