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Egbert Drenth

A/P HDG and ND Heading?

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Hi,During a flight I noticed that the actual heading displayed in the ND differs from the heading set in the A/P.In the picture below a heading on 035 is set but a heading of 040 is flown. Is this due to MagVar or something else?http://forums.avsim.net/user_files/54569.jpgAnother question relating a autolanding.I was in APP mode (dual A/P engaged). The APP light burned untill capturing the G/S, after that the APP light went off.Nevertheless the autoland was flawlessly performed. Bug or feature? http://forums.avsim.net/user_files/54570.jpg

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Look again at first screenshot on the ND, notice there is a little WHITE BUG offset to the left right at 035?? That's your heading. NOT the TRK. WHen APP mode ARMS (with G/S capture) the light GOES OUT just like the real 737 NG. The FMA shows CMD and G/S which is what you must check, not simply the MCP lights which can fail in the real world for any mode, so always regard the FMA annunciations first for MODE engagements.[h4]Best Wishes,Randy J. Smithhttp://www.precisionmanuals.com/images/betaimg.jpg

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Hi Randy,I didn't realised that the track is displayed in the ND.Regarding the APP mode, I guess I should have RTFM ;-)Thanks for your very prompt answer, much appreciated!Take care,Egbert

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Just to elaborate on the APP thing: on Boeing aircraft, at least the ones I know, when a MCP button is illuminated it means that you can deselect it by pushing it again. Now, when the APP mode has become fully active by capturing the G/S you can no longer de-activate the APP mode by simply pushing the button (you'd have to push TOGA, or switch the autopilot and both F/D's off). So the fact that the light goes black actually has a very specific function!Leo Bakker

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"Just to elaborate on the APP thing: on Boeing aircraft, at least the ones I know, when a MCP button is illuminated it means that you can deselect it by pushing it again."....with the proviso that the mode selected is not already engaged ;-) (i.e. the A/P is not already using that mode). When a mode is armed only, you are allowed to deselect it by pushing it a second time. Most Boeings don't like you deselecting engaged modes if there is nothing to replace that mode. Usually you need to select a different mode to get a light to extinguish.Interestingly, I thought, the 737NG allows you to swap between autopilots without disengaging the first autopilot (during single A/P ops). e.g. If A is in CMD, you can simply push the B CMD button to engage B and disengage A (or at least that's how I interpret the Boeing Maintenance Manual).Cheers.Ian.P.S. (Edit) In PMDG, pushing an active A/P mode button forces the A/P into CWS mode. I don't know if this is correct (My notes indicate that there are only three ways to enter CWS mode:1. Push the CWS A/P engage switch2. Push the CMD A/P engage switch and do not select a roll/pitch mode3. When a roll CMD mode is active, apply a wheel force of more than 10lbs (hi detent).Experts: Does "2" include deselecting an armed pitch/roll mode by pushing the mode switch a second time?

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Ian,>>Most Boeings don't like you deselecting engaged modes if there is nothing to replace that mode.<

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Thanks for the tips, Sean :-)"3 -- Yes, but this holds true for "Pitch" also. I believe, however, the pressure is 25 lbs. but might be wrong."I may have overedited my message and left out pitch. My notes list a pressure of 21lbs for CWS pitch mode.I'm wondering if other Boeing aircraft with CWS also change to CWS if pitch/roll modes are deselected when (previously) engaged?I would be interested to know how most people interpret the expression "most Boeings"... i.e. the actual numbers of all (modern) Boeing aircraft manufactured (thousands).... or the number of Boeing models (737, 737NG, 767, 757, 747-400, 777, etc...i.e. 7 or 8 or more) :-)I don't know how prolific 737's are, but could there possibly be more 737's/737NG's produced than all the other models combined? Cheers.Ian.

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