Loss of approach tracking & odd alert

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   I'm starting to learn the nuances of my new IFD540 and ran into a couple of strange things last night.
I was flying the RNAV 18 LNAV approach into KSET using my STEC55X autopilot. I was proceeding direct to LUNGY (the IAF)
and the 55X was in NAV/GPSS mode. Upon reaching LUNGY, the 540 sequenced to a teardrop reversal leg (as charted) and the 55X began the teardrop turn.
However, when it got time to make the turn back inbound, it just kept flying straight ahead. To get things back on track I switched the 55X into heading mode and made the turn using the heading bug. When I got back to the GPS course I switched back to NAV/GPSS and things were fine from then on.
Anyone else experience this?
Also, another oddity...as I was inbound to the FAF at the charted altitude of 2,300', the 540 gave me a yellow warning that my altitude was too low. Why would that be, if I was right at the altitude shown on the approach plate? The only thing I could figure was that the pressure altitude being reported by my transponder was 200' lower than my actual altitude due to the density altitude - could this have triggered the warning?

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bcool Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 30 Nov 2015 Location: St. Charles, MO Status: Offline Points: 35	Post Options Post Reply Quote bcool Report Post Thanks(0) Quote Reply Topic: Loss of approach tracking & odd alert Posted: 05 Apr 2016 at 7:28am
	I'm starting to learn the nuances of my new IFD540 and ran into a couple of strange things last night. I was flying the RNAV 18 LNAV approach into KSET using my STEC55X autopilot. I was proceeding direct to LUNGY (the IAF) and the 55X was in NAV/GPSS mode. Upon reaching LUNGY, the 540 sequenced to a teardrop reversal leg (as charted) and the 55X began the teardrop turn. However, when it got time to make the turn back inbound, it just kept flying straight ahead. To get things back on track I switched the 55X into heading mode and made the turn using the heading bug. When I got back to the GPS course I switched back to NAV/GPSS and things were fine from then on. Anyone else experience this? Also, another oddity...as I was inbound to the FAF at the charted altitude of 2,300', the 540 gave me a yellow warning that my altitude was too low. Why would that be, if I was right at the altitude shown on the approach plate? The only thing I could figure was that the pressure altitude being reported by my transponder was 200' lower than my actual altitude due to the density altitude - could this have triggered the warning?