colohan
Pre-takeoff checklist
- Joined
- Jun 6, 2008
- Messages
- 163
- Display Name
Display name:
Chris Colohan
I am currently training for my IFR rating. Recently I discovered that although I am good at hand-flying the plane, I can mess things up pretty badly when I try to fly using the autopilot. :smile: So I am doing some flights using the autopilot as much as possible (when legal) to make sure I am proficient.
The C172SP I am training in has a KAP140 2-Axis Autopilot. There is one thing I have not yet figured out -- when is the best time to switch from NAV mode to APR mode when intercepting an ILS?
In particular, the ILS approach I use most for practice is ILS 25R into KLVK, starting from TRACY. After passing TRACY and ensuring I am solidly on the right course (and leaving the GPS on to verify...), I switch the autopilot to HDG mode to maintain my present heading, change the #1 CDI to the ILS, and wait for the localizer needle to start to come in.
Now, my question is this: when should I switch the autopilot to APR mode and swing the heading bug to match the course of the ILS?
If I switch the autopilot to APR as soon as the needle starts to come in (or even before), the GPS makes a hard left turn towards the localizer (since it thinks it is suddenly way off course), blows straight through the localizer, makes a hard right to recover, and oscillates several times around the localizer before figuring it out. Not smooth.
If I wait until I intersect the localizer at FOOTO it is too late to turn onto the localizer course, blow straight through it, and the autopilot may refuse to go into APR mode at all.
So is there an optimal technique for making this type of transition with this autopilot? (My instructor just claims "the KAP140 sucks".) Or do I either try to smoothly intercept the localizer by playing with the heading bug in HDG mode, and then put it in APR mode -- or just disable the autopilot and hand fly the plane onto the localizer?
The C172SP I am training in has a KAP140 2-Axis Autopilot. There is one thing I have not yet figured out -- when is the best time to switch from NAV mode to APR mode when intercepting an ILS?
In particular, the ILS approach I use most for practice is ILS 25R into KLVK, starting from TRACY. After passing TRACY and ensuring I am solidly on the right course (and leaving the GPS on to verify...), I switch the autopilot to HDG mode to maintain my present heading, change the #1 CDI to the ILS, and wait for the localizer needle to start to come in.
Now, my question is this: when should I switch the autopilot to APR mode and swing the heading bug to match the course of the ILS?
If I switch the autopilot to APR as soon as the needle starts to come in (or even before), the GPS makes a hard left turn towards the localizer (since it thinks it is suddenly way off course), blows straight through the localizer, makes a hard right to recover, and oscillates several times around the localizer before figuring it out. Not smooth.
If I wait until I intersect the localizer at FOOTO it is too late to turn onto the localizer course, blow straight through it, and the autopilot may refuse to go into APR mode at all.
So is there an optimal technique for making this type of transition with this autopilot? (My instructor just claims "the KAP140 sucks".) Or do I either try to smoothly intercept the localizer by playing with the heading bug in HDG mode, and then put it in APR mode -- or just disable the autopilot and hand fly the plane onto the localizer?