Autopilot Not Tracking GTN750 Approach

[sab12]

I am using the GTN750 in my Cherokee 180

I am trying to make an ILS approach to Runway 34 at NZWN (Wellington, New Zealand) with transition D0710O.

The waypoints on this approach per the GTN750 are D071O, D153O, UMAGA, BUTIN, FI34, RW34.

The autopilot on HI TRK starts the approach and follows the first two waypoints perfectly. However, rather than turning to UMAGA after D153O, the aircraft continues on the course through D153SO.

My A2A Cessna 172 follows the GTN750 approach properly as do my RAS Lancare Legacy and Turbine Duke with the GTN750.

Is this a bug in the STEC 30 or am I doing something wrong?

Thanks,

Steve

[Nick - A2A]

Hello Steve - welcome to the forums.

What you describe isn't a "bug" with the S-TEC 30, but rather a limitation of how the real unit works. Compared with many autopilots modelled in FSX, it's a bit more limited in its capabilities but a very good simulation nonetheless. For instance, it has no capability to track a glideslope.

As far as your specific question on the lateral tracking modes, the S-TEC 30 doesn't have an intercept capability, unlike the KAP 140 for instance; small course changes shouldn't present too much of a problem, but for large ones you'll have to use the 'ST' mode and the 'steering' knob, or disconnect the autopilot and intercept the next leg yourself. this topic gives a little more info.

Cheers,
Nick

[sab12]

Hi Nick,

OK - Will use ST or HD mode to work around when necessary.

I was a bit surprised by what happened since the autopilot did successfully track sharper turns in the flight plan - albeit with some wide swings and recovery.

Like the handling and modelling of the Cherokee a lot. Realizing I'm a bit spoiled by capabilities of other (much pricier in real-world) aircraft I fly in FSX. Opportunity to develop piloting skills a bit more.....

Thanks,

Steve

[Nick - A2A]

Hi Steve,

Yeah, the S-TEC 30 does encourage more 'hand-on' flying and the Cherokee is still a great IFR platform, even with the less capable avionics. I don't know exactly what the simulated AP's limitations are in terms of its tracking behaviour, but another forum member, Esa, made a series of posts on "understanding autopilots" which you may find interesting.

Cheers,
Nick