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After an approach at your destination, the weather is found to be below limits, and you decide to divert to your alternate aerodrome. During initial climb you notice that the leading-edge devices are not completely retracted. After completing all necessary actions to deal with this abnormal condition, you check the FMS for ETA and fuel remaining at the diversion aerodrome. Based on the above, you can..
  • A
    Use the FMS time predictions, but you can NOT use the fuel predictions.
  • B
    NOT use the FMS time predictions, but you can use the FMS fuel predictions.
  • C
    NOT use any of the FMS time or fuel predictions.
  • D
    Use both the FMS time and fuel predictions.

The fuel prediction logic of the FMS is predicated on the aircraft being in what is considered to be the “normal” configuration for the phase of flight. However, under circumstances of Abnormal Aircraft Configuration, such as slats not retracting, the fuel predictions are no longer accurate. Failure to realize this situation has lead crews to make false assumptions about their range and endurance and has been a contributory cause factor in several accidents and incidents.

The ETA prediction is calculated based on groundspeed and distance from the active waypoint, therefore it will not be affected.

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