Boeing/GE has completed the FMC BITE and QAR data analysis for Airplane B-2xxV for the reported event dated 24-Mar-2023. The analysis indicates FMC sent an conflicting altitude target constraint to the Autopilot while in descent to prevent the airplane from descent and to deviate from the vertical path. This is a known software anomaly with FMC OPS U13 and prior and is listed in 737NG-FTD-34-19003. Further, we confirm that this issue has been fixed in FMC OPS U14.
波音对于机组操作的建议如下:
As stated in 737NG-FTD-34-19003, operators can review the specific procedure for the presence of AT/ABOVE altitude constraints. If AT/ABOVE constraints are identified, operators can contact their NDB supplier to determine what, if any, change can be made within the NDB to replace AT/ABOVE with AT constraints. Crews should follow the attached FCTM Stabilized Approach Recommendations and Mandatory Missed Approach recommendations, which include: executing a missed approach on an RNP based approach and an alert message indicates that ANP exceeds RNP; for airplanes with NPS, during RNP approach operation, anytime the NPS deviation exceeds the limit or an amber deviation alert occurs unless the aircrew is able to change to a non-RNP procedure; for airplanes with FMC U14 or later, during RNP AR approaches, with or without NPS, anytime the UNABLE REQD NAV PERF-RNP is shown during the approach, regardless of whether or not the lateral or vertical RNP are exceeded; and for airplanes without NPS, during RNP approach operation, anytime the XTK exceeds 1.0 X RNP unless the aircrew is able to change to a non-RNP procedure.