Narrative:

Shortly after checking on to frequency on the fissk four RNAV arrival into mdw we heard the end of an exchange with ATC about a waypoint being a fly by vs fly over waypoint. This put me on a slightly higher alert for the arrival. The sic was busy programming the FMS for the expected runway. I noticed the course from troly to gotne disappeared from the mfd screen and the airplane began a slow early turn to intercept a course from gotne to fissk. We were also on a descent clearance to make a lower crossing restriction. I wasn't at that moment sure if we had caused the error during FMS programming or not. I immediately asked ATC if they needed me over gotne or not because the plane was either making a very early smart turn or dumping the arrival. ATC issued a new clearance and reestablished us on the arrival. He queried if we thought there was a coding issue with the arrival or our error. We advised we were still working that out for certain. ATC said that he was hearing that we were not the first aircraft to have that issue. After a review we could not find any reason for the malfunction. I believe the coding for this portion of the arrival needs to be reviewed. The only other possibility that I did not check and subsequently changed planes is the default flight config page. Though I feel certain that there is some type of coding error on this leg in the database there are two other possible contributing possibilities to consider. 1. This flight occurred on the day of chart revision page change over. While I don't think this actual arrival was due to change maybe some other route that also uses this segment has changed. 2. I have seen an increase in the number of airplanes that the default flight config has been changed to 7 vs 15 degrees of bank. This does cause aircraft to turn shallower enroute. This effect is most amplified as the turn approaches 90 degrees. The flight config can be changed by flight crew but I have experienced a few instances where the avionics defaults to 7 degrees after a power cycle. I did not think to check this on the affected airplane. Many times the aircraft lose the last settings for things like flight director preferences after a full shut down or a temporary but slightly longer than normal red 'x' on FMS 1 after power up etc. This may cause flight config to also reset to 7 degrees of bank which according to the honeywell manual is the default. We may need to add this to the after start check if it's found to be common.

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Original NASA ASRS Text

Title: CE-680 Captain reported a track deviation resulted from either a miscoded arrival or the aircraft's 'smart turn' characteristics.

Narrative: Shortly after checking on to frequency on the FISSK FOUR RNAV arrival into MDW we heard the end of an exchange with ATC about a waypoint being a fly by vs fly over waypoint. This put me on a slightly higher alert for the arrival. The SIC was busy programming the FMS for the expected runway. I noticed the course from TROLY to GOTNE disappeared from the MFD screen and the airplane began a slow early turn to intercept a course from GOTNE to FISSK. We were also on a descent clearance to make a lower crossing restriction. I wasn't at that moment sure if we had caused the error during FMS programming or not. I immediately asked ATC if they needed me over GOTNE or not because the plane was either making a very early smart turn or dumping the arrival. ATC issued a new clearance and reestablished us on the arrival. He queried if we thought there was a coding issue with the arrival or our error. We advised we were still working that out for certain. ATC said that he was hearing that we were not the first aircraft to have that issue. After a review we could not find any reason for the malfunction. I believe the coding for this portion of the arrival needs to be reviewed. The only other possibility that I did not check and subsequently changed planes is the default flight config page. Though I feel certain that there is some type of coding error on this leg in the database there are two other possible contributing possibilities to consider. 1. This flight occurred on the day of chart revision page change over. While I don't think this actual arrival was due to change maybe some other route that also uses this segment has changed. 2. I have seen an increase in the number of airplanes that the default flight config has been changed to 7 vs 15 degrees of bank. This does cause aircraft to turn shallower enroute. This effect is most amplified as the turn approaches 90 degrees. The flight config can be changed by flight crew but I have experienced a few instances where the avionics defaults to 7 degrees after a power cycle. I did not think to check this on the affected airplane. Many times the aircraft lose the last settings for things like flight director preferences after a full shut down or a temporary but slightly longer than normal red 'x' on FMS 1 after power up etc. This may cause flight config to also reset to 7 degrees of bank which according to the Honeywell manual is the default. We may need to add this to the after start check if it's found to be common.

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.