KAP 140 Issue

[John Benzon]

I just bought a C182 with a Garmin 530 and a KAP 140 two axis auto pilot with Alt hold. On a recent flight, I was using NAV mode. To track the GPS TK, I had to adjust my heading on the HSI from the DTK by 16 degrees. I had the following information:
GPS TK 359
GPS DTK 359
Compass hdg 350
HSI hdg 343
CDI 332

Before I head to the avionics shop, I would like to find out whether anyone else has ever encountered this problem.

[IO540]

Your description is a little ambiguous but are you aware that the heading will differ from the track, if there is any crosswind present?

Also, the magnetic compass is often way off. One can calibrate it on the ground as much as one wants but it then shifts maybe 5-10 degrees in flight if there is electrical wiring nearby carrying significant currents.

In NAV move, the heading bug should be ignored.

I have a KFC225, BTW.

[wigglyamp]

Does your 182 have an HSI or CDI for displaying the GPS. In either case, the CDI course should be set to the desired track.

[Big Pistons Forever]

Originally Posted by John Benzon

I just bought a C182 with a Garmin 530 and a KAP 140 two axis auto pilot with Alt hold. On a recent flight, I was using NAV mode. To track the GPS TK, I had to adjust my heading on the HSI from the DTK by 16 degrees. I had the following information:
GPS TK 359
GPS DTK 359
Compass hdg 350
HSI hdg 343
CDI 332

Before I head to the avionics shop, I would like to find out whether anyone else has ever encountered this problem.

I am having a bit of trouble wrapping my head around what you have posted. Please do not take this the wrong way but it appears to me that you need to review how your systems work.

First off if you are in autopilot NAV mode then the autopilot will adjust the heading to center the HSI needle. Therefore the head of the track bar of HSI should be set to DTK (Direct track ie a straight line from where you are to the destination waypoint in the GPS), or in this case 359 not 332.

It is also important to note that the HSI track bar is driven by 2 completely different nav inputs. "nav" means that the track bar is sensing a VOR or localizer, while "GPS" means the GPS is driving the bar. There will be a mode selector on your panel and you have to make sure you have it correctly set, "GPS" in this case. This switch can be a bit of a "suicide" switch when flying IFR and there have been numerous accidents caused by the pilot was following the wrong track bar indication because the mode switch was set to the wrong source.

Also the heading bug does not control the autopilot in Nav Mode. The autopilot does what it has to do to keep the HSI track bar in the center. When everything settles down you will probably find that the autopilot is steering a heading that is different than the what the HSI track bar is set for, the difference represents the wind correction that the autopilot has put in.

I would not expect that the mag compass will perfectly aligned with the HSI. The HSI gets it heading information from the flux gate while the mag compass obviously senses the earths magnetic field directly and so a few degrees difference between the two is normal, although in your case the 7 degrees between the mag compass and the HSI is getting a bit much. Comparing the two headings when lined up with the runways actual heading should be part of the line up check. significant errors mean both the HSI and the mag compass should be adjusted with a compass swing.

As a final note I never use the autopilot heading Nav mode instead I always use the heading mode adjusting the heading as required to keep the track bar centered. This keeps me in the loop and makes me aware of what the wind is doing. In practice I spend most of my time comparing the GPS bearing and track data block. I simply turn the aircraft until the aircraft track course is the same as the bearing.

GA GPS's all have significantly different operating methodologies, I know because I have to remain current on 5 different boxes (KLN 900, KLN 89, KLN94, Garmin 530/430, and an ancient 2Morrow 2001 NMS). If the kit is new to you I highly recomment you get some training with an instructor that has personal experience operating the unit you have