Narrative:

CHSLY3 RNAV arrival to ILS 18L; light headwind component. Managed descent speed programmed 280kt. Prior to descent; f-pln profile page projected altitudes 400-800ft low at burzz; sekls; and dentt (with an amber *). All restraints were accurately displayed on the pfd. When descent was initiated; manual intervention was indeed required to comply with the charted restraints.on the following day on another A319; CHLSY3 ILS 18L under similar conditions; a similar VNAV path error was projected. Moreover; once descent was initiated; the performance page reverted to a managed descent speed of 230 kt. Descent speed could not be modified; even though the speed was displayed. The descent was flown in selected speed and V/south until passing dentt; at which time managed descent and selected speed resulted in a compliant VNAV arrival and transition to the ILS. We cannot account for the VNAV errors on these descents. All pilot entries were made in the usual manner. The required chsly 3 VNAV path is routine; and not particularly steep. The airplane was in fact capable of flying a compliant descent without spoilers when flown manually. We did not see the more drag message at any time.FMS database or functionality of VNAV descent software.in the on-going effort to evaluate and manage the airbus VNAV descent path anomalies; I would like to see specific procedural guidance for crews when the FMS will not; for whatever reason; comply with the required path. Should a 'descend via...' clearance be declined? Or altitude stepped down incrementally combined with V/south? Most of the RNAV arrivals have multiple above/below constraints; and attempting to intervene to manage the path is a high-workload; potentially deviant operation. Automation taking the crew 'into the yellow' by design?

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Original NASA ASRS Text

Title: A319 Captain would not fly the VNAV path profile for this arrival without pilot intervention. Prior to descent the profile projected pilot intervention would be needed and the projection was correct.

Narrative: CHSLY3 RNAV Arrival to ILS 18L; light headwind component. Managed descent speed programmed 280kt. Prior to descent; F-PLN profile page projected altitudes 400-800ft low at BURZZ; SEKLS; and DENTT (with an amber *). All restraints were accurately displayed on the PFD. When descent was initiated; manual intervention was indeed required to comply with the charted restraints.On the following day on another A319; CHLSY3 ILS 18L under similar conditions; a similar VNAV path error was projected. Moreover; once descent was initiated; the Performance page reverted to a managed descent speed of 230 kt. Descent speed could not be modified; even though the speed was displayed. The descent was flown in selected SPD and V/S until passing DENTT; at which time managed descent and selected speed resulted in a compliant VNAV arrival and transition to the ILS. We cannot account for the VNAV errors on these descents. All pilot entries were made in the usual manner. The required CHSLY 3 VNAV path is routine; and not particularly steep. The airplane was in fact capable of flying a compliant descent without spoilers when flown manually. We did not see the MORE DRAG message at any time.FMS Database or functionality of VNAV descent software.In the on-going effort to evaluate and manage the Airbus VNAV descent path anomalies; I would like to see specific procedural guidance for crews when the FMS will not; for whatever reason; comply with the required path. Should a 'descend via...' clearance be declined? or ALT stepped down incrementally combined with V/S? Most of the RNAV arrivals have multiple above/below constraints; and attempting to intervene to manage the path is a high-workload; potentially deviant operation. Automation taking the crew 'into the yellow' by design?

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.