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benh320

LNAV/VNAV Issues

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Problem 1

 

Had the same problem at the start of 3 flights. Different weights, airports, SIDs so that doesn't seem to be the problem. Basically take off as normal, arm LNAV/VNAV a few seconds after departure all is well until after a few mins (probably around 5/6000ft) I go direct to a waypoint using the FMC. Basically the autopilot doesn't know what to do it just keeps turning left until bank angle aural sounds and keeps banking! I have to disconnect the autopilot, then select HDG SEL and then LNAV again and all is good for the rest of the flight! very strange behavior - only even happens straight after departure so not sure what the problem in is!. It has nothing to do with my controller - all perfectly calibrated. Using AS2012 - never seen this on any other aircraft.

 

Problem 2:

 

VNAV arrival, had a last min change of arrival runway into BOS last night about 50nm before T/D so made the change and it totally screwed up VNAV to show that my VDEV was minus what my actual flight level was at the time so if I was at 36000ft my VDEV was -36000ft ! very strange. It also wanted to reduce my speed to 212kts at 36000ft! Nothing I could do could resolve the issue - deleting all the altitude and speed constraints, making new ones, copying route to RTE2 then activating - my VNAV was totally unusable for the whole descent! Weirdly enough the FMC showed the correct value it was just the autopilot and ND that were way off!

 

Few pics of the VNAV prob:

 

 

2-6.jpg

 

[url=http://s11.photobucket.com/user/benhewitt_sun/media/1-6.jpg.html]1-6.jpg[/url

 

Cheers

 

Ben

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