Narrative:

[We] departed runway 34L at sea via the SUMMA7 SID. FMS was programmed for runway 34L and SUMMA7 departure prior to taxiing. Aircraft was selected to depart in LNAV mode since the entire departure loaded properly in the FMS as confirmed by cross-checking the commercial navigation chart. We confirmed the FMS indicated an initial climb on a 343 course; comparing to the charts 346 degrees it was within the 3 degrees acceptable variance allowed when using an RNAV database for a flight management system. We felt the departure was coded correctly and that the minor variance was nominal. After lift-off the flight director commanded a right turn to fly the 343 intercept course to further intercept the 341 inbound course to nezug; the pilot flying followed the flight director commands in the HUD after liftoff. After several seconds in the right turn it became apparent that the flight director was commanding too aggressive of a right turn after liftoff to intercept the course inbound to nezug fix and we proceeded to turn back to the left as we were heading for the adjacent runway departure paths; which we felt was incorrect. (The flight director was still commanding a slight right turn at that point). Fortunately it was VFR and we were able to clearly see our ground path which helped us determine that we were being lead too far to the right. As we were correcting ATC inquired about which departure we were assigned; we confirmed the SUMMA7 and then we asked if there was an issue; they responded that there was no issue and handed us off to departure. Based on our later examination; we estimate that our lateral deviation was less than 0.3 NM from the expected course; well within RNAV1/RNP1 limits. After we continued the departure and arrived at cruise altitude we elected to continue our investigation as to why the FMS/flight director seemed to take us too hard to the right after departure. We confirmed that we had the proper runway and departure programmed into our FMS's. After looking at the same departure (SUMMA7) for the 2 other runways (runway 34C and runway 34R) in the FMS database; it came to our attention that all 3 runways are coded in the FMS navigation database exactly the same even though the initial climb for each runway is slightly different. All 3 runways are coded as a 343 course to intercept the 341 inbound course to nezug waypoint. This programming anomaly/error caused the flight director to command a right turn that was far too aggressive when departing runway 34L. Human factors issues are relying on the FMS/flight director guidance; however we were able to fairly quickly ascertain the error and apply corrective action back to the left. There were no other aircraft in our vicinity and no other conflicts occurred; merely the query from ATC regarding our assigned departure. Corrective action would be to re-evaluate the FMS database coding for the 3 runways in this departure to ensure proper guidance.

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Original NASA ASRS Text

Title: G450 flight crew reports a possible track deviation while departing SEA from Runway 34L on the SUMMA7 departure. The pilot flying followed the Flight Director command initially in a gentle right turn until it was perceived to be too much and was questioned by ATC. In flight analysis revealed that the procedure and runway had been loaded correctly and that procedure coding in the FMC may be an issue.

Narrative: [We] departed Runway 34L at SEA via the SUMMA7 SID. FMS was programmed for Runway 34L and SUMMA7 departure prior to taxiing. Aircraft was selected to depart in LNAV mode since the entire departure loaded properly in the FMS as confirmed by cross-checking the Commercial Navigation Chart. We confirmed the FMS indicated an initial climb on a 343 course; comparing to the charts 346 degrees it was within the 3 degrees acceptable variance allowed when using an RNAV database for a Flight Management System. We felt the departure was coded correctly and that the minor variance was nominal. After lift-off the Flight Director commanded a right turn to fly the 343 intercept course to further intercept the 341 inbound course to NEZUG; the pilot flying followed the Flight Director commands in the HUD after liftoff. After several seconds in the right turn it became apparent that the Flight Director was commanding too aggressive of a right turn after liftoff to intercept the course inbound to NEZUG fix and we proceeded to turn back to the left as we were heading for the adjacent runway departure paths; which we felt was incorrect. (The Flight Director was still commanding a slight right turn at that point). Fortunately it was VFR and we were able to clearly see our ground path which helped us determine that we were being lead too far to the right. As we were correcting ATC inquired about which departure we were assigned; we confirmed the SUMMA7 and then we asked if there was an issue; they responded that there was no issue and handed us off to Departure. Based on our later examination; we estimate that our lateral deviation was less than 0.3 NM from the expected course; well within RNAV1/RNP1 limits. After we continued the departure and arrived at cruise altitude we elected to continue our investigation as to why the FMS/Flight Director seemed to take us too hard to the right after departure. We confirmed that we had the proper runway and departure programmed into our FMS's. After looking at the same departure (SUMMA7) for the 2 other runways (Runway 34C and Runway 34R) in the FMS Database; it came to our attention that all 3 runways are coded in the FMS NAV Database exactly the same even though the initial climb for each runway is slightly different. All 3 runways are coded as a 343 course to intercept the 341 inbound course to NEZUG waypoint. This programming anomaly/error caused the Flight Director to command a right turn that was far too aggressive when departing Runway 34L. Human factors issues are relying on the FMS/Flight Director guidance; however we were able to fairly quickly ascertain the error and apply corrective action back to the left. There were no other aircraft in our vicinity and no other conflicts occurred; merely the query from ATC regarding our assigned departure. Corrective action would be to re-evaluate the FMS Database coding for the 3 runways in this departure to ensure proper guidance.

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.