PPRuNe Forums - View Single Post - Act xxx Lim CRZ - What does it mean?
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Old 6th Dec 2020, 14:52
  #11 (permalink)  
eckhard
 
Join Date: May 2005
Location: France
Age: 69
Posts: 1,143
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I don't think so.

As far as I remember, the ACT XXX LIM CRZ (or CLB or DES) takes into account the gear position and the flap position. When I say, "position", I don't know whether the FMC is referencing the actual achieved position of the gear/flaps or the maybe only the position of the lever.

With the gear and flaps up, there is no LIM speed (in this context). To be clear, I don't think that the FMC will protect the aircraft from inadvertent extension of gear/flaps at too high an airspeed, so it's still up to the pilots to respect those limits before making the selection. Once the configuration has been achieved, the FMC VNAV function will prevent overspeed.

With only the gear down (flaps up), the LIM speed should be that for flight with gear extended, or Vle.
With only flaps extended (gear up), the LIM speed should be that for the flap position achieved.
With both gear and flaps extended, the LIM speed should be the lowest of the two speeds.

Normally, the gear is only down when the flaps are extended, so the LIM speed will be that for the flaps. If your sim is showing a LIM of 230 with the flaps up and the gear up but with the gear lever in the UP position, it may be that the LIM speed is that for gear retraction (Vlo). The sim programme is interpreting the gear lever position as an intention to retract the gear and is therefore displaying that speed (230) on the FMC CDU VNAV page.

You could try a flight with the gear up and the lever in the OFF position. Then see if flap extension changes the LIM speed as I have described.
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