Narrative:

After verifying the correct runway and RNAV departure (8R; summt 5) in atl; and selecting the flight guidance panel to sub-mode; FMS and navigation; coupled to the first officer's side. We were cleared for takeoff with a clearance to RNAV to ronii. I read back that clearance and we departed. At 500 ft we engaged the autopilot and the aircraft made a slight turn to the right; nothing excessive. The airplane then tracked towards ronni and at acceleration altitude we cleaned up the airplane. Soon thereafter we were told by the tower to make an immediate 15 degree left turn. We did. The tower then asked us if we were showing to be off course. I told them that we were showing us on course. We were given another heading and then a re-intercept back to the RNAV departure. Remainder of the flight was uneventful.I believe there is a difference in our software and what ATC desires from us. The RNAV departures are telling us to fly a heading to an intercept and that's what the airplane will do; but; it's my belief that ATC wants us to track that heading as if it were a course. Not sure; but that's my thought. Another issue is that it's not uncommon in these airplanes to make an initial slight turn in the opposite direction in order to make a course intercept. Not very good when your trying to fly rnavs.

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Original NASA ASRS Text

Title: An E145 flight crew climbing on a heading of 092 degrees to intercept course 079 into RONII per the SUMMT RNAV SID from ATL was advised of a course deviation by the Tower despite the fact their Nav Display showed them to be following the procedure as published.

Narrative: After verifying the correct runway and RNAV departure (8R; SUMMT 5) in ATL; and selecting the flight guidance panel to sub-mode; FMS and NAV; coupled to the First Officer's side. We were cleared for takeoff with a clearance to RNAV to RONII. I read back that clearance and we departed. At 500 FT we engaged the autopilot and the aircraft made a slight turn to the right; nothing excessive. The airplane then tracked towards RONNI and at acceleration altitude we cleaned up the airplane. Soon thereafter we were told by the Tower to make an immediate 15 degree left turn. We did. The Tower then asked us if we were showing to be off course. I told them that we were showing us on course. We were given another heading and then a re-intercept back to the RNAV departure. Remainder of the flight was uneventful.I believe there is a difference in our software and what ATC desires from us. The RNAV departures are telling us to fly a heading to an intercept and that's what the airplane will do; but; it's my belief that ATC wants us to track that heading as if it were a course. Not sure; but that's my thought. Another issue is that it's not uncommon in these airplanes to make an initial slight turn in the opposite direction in order to make a course intercept. Not very good when your trying to fly RNAVs.

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.