Narrative:

On takeoff leg of this departure; engaged navigation at 400 ft AGL (1;540 ft MSL) and autopilot on at 5;000 ft AGL. Tower called us just above 500 ft and told us it looked like we were tracking left of the course track and we needed to track further right for the initial transition. The aircraft was on a 280 bearing and verified on course on the navigation display and the pfd. FMA navigation trk; and progress page 2 of the FMS (0.06NM left of track). We were given the frequency change to departure and upon check in we were requested to call tower upon arrival. I called. He was very professional and was looking for information on how we flew and tracked the RNAV departure. His concern was that it appeared; from his visual cues in the tower; that we tracked left before turning right on course. He also explained that this is a common occurrence on our carrier's MD80 aircraft and not on another carrier's. I explained the departure initial heading; when we engaged the navigation and autopilot; and what we monitor to make sure we are tracking the course accurately. His main concern is obviously the safety zone between the north and south runways. I believe I followed RNAV procedures as per company directives. But somewhere in the transition from navigation capture and track and autopilot on for the RNAV departures to the west; that small delay may cause the aircraft to track too slowly to the desired transition course.

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Original NASA ASRS Text

Title: A MD80 flight crew reported that their aircraft's slow FMS processor does not have time to update on an RNAV departure before the 1;540 turn point and as a result turns slight later than ATC expects; causing a track deviation.

Narrative: On takeoff leg of this departure; engaged NAV at 400 FT AGL (1;540 FT MSL) and autopilot on at 5;000 FT AGL. Tower called us just above 500 FT and told us it looked like we were tracking left of the course track and we needed to track further right for the initial transition. The aircraft was on a 280 bearing and verified on course on the NAV display and the PFD. FMA NAV TRK; and progress page 2 of the FMS (0.06NM left of track). We were given the frequency change to Departure and upon check in we were requested to call Tower upon arrival. I called. He was very professional and was looking for information on how we flew and tracked the RNAV departure. His concern was that it appeared; from his visual cues in the Tower; that we tracked left before turning right on course. He also explained that this is a common occurrence on our carrier's MD80 aircraft and not on another carrier's. I explained the departure initial heading; when we engaged the NAV and autopilot; and what we monitor to make sure we are tracking the course accurately. His main concern is obviously the safety zone between the north and south runways. I believe I followed RNAV procedures as per company directives. But somewhere in the transition from NAV capture and track and autopilot on for the RNAV departures to the west; that small delay may cause the aircraft to track too slowly to the desired transition course.

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.