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scottb613

GTN and the dreaded Holding Pattern ?

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Al,

 

I do not recall any published reference as to what distance or angular offset is required for a NAV capture so I can not comment on what it would be.With a VOR radial or an ILS the autopilot would typically switch from arm to capture once the CDI was alive and had movement.With GPS when a leg or procedure was activated NAV would capture when selected, the only exception I can think of would be using a GPS OBS mode.You could specify intercepting a specific radial to or from a fix, use HDG to establish the intercept angle, select NAV and it would capture when reaching the desired track.

 

There was a preflight test with the earlier FC-200 autopilot where you test the NAV arm and capture function using a valid VOR signal on the ground by simulating an intercept and capture.Set the CDI full scale off center, select the HDG and NAV arm as though you are on an established intercept angle to the radial, then slowly rotating the course knob to bring the CDI towards the center and verifying the NAV capture occurs.You can do the same thing with the the FSW L35 530 autopilot and the default GNS 530 will fly a full procedure turn and hold although not very pretty to watch how it does it.I don't have the GTN, maybe load up the stock version and see what you get.


Gary Stewart

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Gary,

 

I think L35A Nav capture, as far as VORs and Localizers are concerned, works fine and as you have described -- capture happens when the CDI is alive.

 

It has been with the NAV GPS mode that I have been experimenting. I now have 3 different cab file versions:

 

- the first one just expands the original FSW 2NM GPS capture range to either 6 or 10NMs (the 10NM value allows for higher speed holding pattern turns). Get anywhere in that range and GPS capture happens.

- the second one has an initial 2NM capture range requirement (the original FSW value), but then holds GPS capture out to some extended range (either 6 or 10 NMs). If you exceed the extended range then GPS recapture requires you to get back within the initial 2NM range.

- the third version is like the second one with an initial 2NM capture requirement, but if you exceed the extended 6 or 10 NM GPS range, GPS recapture only requires that you get back within the extended range, not the initial 2NM range.

 

I probably like the third option best, although I can't clearly articulate why (except maybe like with the VOR/Localizer, you need to be 'reasonably close' to your course for at least initial capture, and recapture is easy). I'll use it for awhile and see if there might be unintended consequences. In any case, it is kind of fun to experiment a bit. I really like the L35A.

 

Thanks very much for you input,

 

Al

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