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Commercial fixed wing captain reported not maintaining assigned mach number after level off from descent. The FMC reset to economy cruise as this carrier has apparently configured their FMC's to do.
| Attributes | |
| ACN | 842343 |
| Time | |
| Date | 200906 |
| Local Time Of Day | 0001-0600 |
| Place | |
| Locale Reference | LEGGT |
| State Reference | FL |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | Commercial Fixed Wing |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | FMS/FMC |
| Person 1 | |
| Function | Captain |
| Experience | Flight Crew Last 90 Days 200 Flight Crew Type 22800 |
| Events | |
| Anomaly | Deviation - Procedural Clearance Deviation - Speed All Types |
Narrative:
We were assigned a speed of .77 mach by center. The autothrottle was engaged so when we were cleared from our cruising altitude of 35;000 ft to 31;000 ft we used the descend now option. As we descended; we were approaching a major area of weather; and we were distracted by this as the autopilot leveled off. The autothrottle system reset our cruise speed to max economy cruise (.72 mach). As we were distracted by the severe weather ahead; we failed to notice the decrease in cruise airspeed. Shortly ATC called and inquired about our speed. We replied .72 at which point he stated that we were supposed to be maintaining .77. The controller stated that this was not the first time recently that this had happened and he was curious why this was happening. I explained that it might be due to our conversion to a full up autothrottle system that is programmed to reset to economy cruise when it levels off at a new altitude after decent. Apparently we are not the only people to have this happen so it may need to be addressed in our review of procedures
Original NASA ASRS Text
Title: Commercial fixed wing Captain reported not maintaining assigned Mach number after level off from descent. The FMC reset to economy cruise as this carrier has apparently configured their FMC's to do.
Narrative: We were assigned a speed of .77 Mach by Center. The autothrottle was engaged so when we were cleared from our cruising altitude of 35;000 FT to 31;000 FT we used the descend now option. As we descended; we were approaching a major area of weather; and we were distracted by this as the autopilot leveled off. The autothrottle system reset our cruise speed to max economy cruise (.72 Mach). As we were distracted by the severe weather ahead; we failed to notice the decrease in cruise airspeed. Shortly ATC called and inquired about our speed. We replied .72 at which point he stated that we were supposed to be maintaining .77. The Controller stated that this was not the first time recently that this had happened and he was curious why this was happening. I explained that it might be due to our conversion to a full up autothrottle system that is programmed to reset to economy cruise when it levels off at a new altitude after decent. Apparently we are not the only people to have this happen so it may need to be addressed in our review of procedures
Data retrieved from NASA's ASRS site as of April 2012 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.