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Roger C

E175/195 VNAV will not engage

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I have been operating my E jets without issues for quite awhile, but lately I am encountering a situation where once I load a flight plan and conduct the PERF INIT the FMS displays a message to CHECKm DEST FUEL and shows a negative fuel amount for arrival.  However, once I am airborne the PROG page will show the proper arrival fuel amount.

In addition, and more troubling, is that VNAV will not engage.  Pressing the VNAV button activates an immediate VNAV DISCONNECT message and I have to use V/S fto climb .Also the computation of TOD point is incorrect.  On the last flight it stated the TOD point from a cruise level FL260 to be 15 miles from the destination.  It remained that way even though I programmed in a 10,000' command for 30 miles from the destination.

 

The VNAV does seem to "wake up" once I am ready to initiate descent in that it will start descending even though I am not yet at the predicted (but incorrect) TOD point.

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21 hours ago, Roger C said:

VNAV will not engage.  Pressing the VNAV button activates an immediate VNAV DISCONNECT message

the autopilot will disconnect if the yoke isn't centered.  be sure that you have trimmed the aircraft so the yoke is centered (ie, the plane is in a balanced climb) before activating VNAV.  this disconnect behavior is just like the real aircraft.

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I appreciate the response and while the flight controls were recently calibrated with FSUIPC I will check to ensure all is in balance and trim.  One question: is this failure to engage only for the VNAV?  The autopilot does engage for HDG and LNAV mode with no problem so perhaps it is just the elevator centering that is not accurately trimmed..

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I took a flight yesterday without changing any settings and everything worked fine so I will defer further investigating until/if the problem crops up again.

 

Thanks for the responses.  Very much appreciated.

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