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Captain reported procedural issues with the FMS on the 737-maximum in reference to descent capabilities.
| Attributes | |
| ACN | 1488017 |
| Time | |
| Date | 201710 |
| Local Time Of Day | 1201-1800 |
| Environment | |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | B737 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | FMS/FMC |
| Person 1 | |
| Function | Captain Pilot Flying |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Type 522 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Deviation - Procedural FAR |
Narrative:
During training; for the 737-maximum there was no mention that using the altitude intervention (altitude intv) button would change the FMC altitude. However; when we entered a lower altitude from cruise altitude and selected the altitude intv button; the MCP altitude was entered into the FMC. When we received a new lower altitude and entered it in the MCP and with VNAV selected the aircraft did not start a descent like previous ng aircraft.we noticed that the FMC had a new cruise altitude that we had not entered through the FMC. (The altitude had automatically been entered from the MCP.) we selected the altitude intv button to allow the aircraft to descend again. This happened two or three times. This safety issue was unexpected and could lead to an altitude violation and safety hazard. 737-maximum frm (fault reporting manual) 4.1.3 item 10 altitude intervention switch: under 'push-(during VNAV cruise)' states: 'lower FMC cruise altitude cannot be entered using altitude intv switch.' our aircraft did reset the FMC altitude with the altitude intv switch.
Original NASA ASRS Text
Title: Captain reported procedural issues with the FMS on the 737-MAX in reference to descent capabilities.
Narrative: During training; for the 737-MAX there was no mention that using the Altitude Intervention (ALT INTV) button would change the FMC altitude. However; when we entered a lower altitude from cruise altitude and selected the ALT INTV button; the MCP altitude was entered into the FMC. When we received a new lower altitude and entered it in the MCP and with VNAV selected the aircraft did not start a descent like previous NG aircraft.We noticed that the FMC had a new cruise altitude that we had not entered through the FMC. (The altitude had automatically been entered from the MCP.) We selected the ALT INTV button to allow the aircraft to descend again. This happened two or three times. This safety issue was unexpected and could lead to an altitude violation and safety hazard. 737-MAX FRM (Fault Reporting Manual) 4.1.3 item 10 Altitude Intervention switch: under 'push-(during VNAV cruise)' states: 'Lower FMC cruise altitude cannot be entered using ALT INTV switch.' Our aircraft DID reset the FMC altitude with the ALT INTV switch.
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.