AFS 4500 and TruTrak Vizion

[ALagonia]

Two questions:
When flying a coupled LPV approach -
1. Since the TruTrak Vizion 385 A/P only intercepts the glide slope From below does that mean we must descend a little below the FAF altitude? Example: the altitude at the FAF is 3500. Must I descend to 3400 prior to the FAF In order to intercept the G/S? Or if I am at 3500 prior to reaching the FAF will the A/P intercept the G/S?
2. The AFS is in Vertical Alt while flying from the IAF to the FAF must I manually switch to Vertical Arm or will the EFIS switch automatically? If I must switch manually at what point should I make the change to Vertical Arm?

[FireMedic_2009]

When it states you must intercept the glide slope from below, it means the glide slope is above you (the glide slope is coming from the airport up at an angle, usually 3 deg).

Prior to reaching the approach fix (AF) you have already armed the AP and have loaded your approach either to an IAF or Vectors To and are using the heading bug to steer your plane as ATC is directing you for vectors. The AP will be in either NAV mode or heading/track mode with NAV highlighted on your efis AP screen which means when the you get close to the AF the AP will automatically transition from Heading/Track mode to NAV mode. So if for example the approach fix is 3500', you are at 3500' prior to reaching the AF, the glide slope is above you and you will intercept it when you reach the AF. The vertical altitude on the AP will arm automatically and bring you down the gs.

Let's say you are instead of 3500' but at 3600' and are 3 or 5 miles from the AF, the glide slope will still be above you and you will intercept the glide slope prior to reaching the AF, the AP's vertical altitude will still arm and bring you down the glide slope. I believe the AP requires you to be below the glide slope for 5-7 sec prior to intercepting the glide slope for the vertical altitude to arm.

Hope this helps. The best way to fully understand is go out a fly approaches under VFR. You don't need ATC to shoot approaches under VFR. Remember for your efis to transition from heading mode to NAV mode you must be 30 deg or less from intercepting course line. If not you will blow right through the course line. Also you should be 3 to 5 miles from the FAF upon intercepting the course line for the AP to properly arm assuming you are using vectors to the FAF.

Daren

[ALagonia]

Thank you for clarifying. I have flown some approaches but was wondering more about the automatic switch to Ver Arm.

[amekler]

i have the same set up
the gs will arm and come down from the top-so yes you will be below the glide slope
you have it in vert arm to couple otherwise it will not follow gs
it will switch automatically to vnav
also make sure you put the proper minimum altitude in and be careful
the ap will level off at minimum altitude and airspeed will decrease
hope this helps
A. Mekler
RV10 N668G