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Garmin introduces retrofit autopilots (GFC500 and GFC600)

My DFC90 installation has the flap wire installation. It cost around € 500. Should be very similar for the GFC500. The good thing is that the Autopilot can (and is approved to) fly the airplane with full flaps.

Last Edited by at 20 Jul 08:29

For the DFC90 in the C182, there is a microswitch and a bracket which you rivet to the flap switch so it gets mechanically actuated by the flap switch. Crude way but 100% electrically decoupled

Whenever I retract the flaps immediately after touchdown, the lady starts screaming UNDERSPEED.

Yes, that can be annoying, it also starts when I do a really slow final approach for a short strip: “Underspeed”…“Underspeed”. But the volume for he voice can be changed through a setting on the PFD in the Cirrus.

Can you access those settings through the Aspen?

Flap position is easy. Even the KFC225 has a flap position input (not used in the TB installs). The KFC325 has an IAS input, to modify the control loop properties according to speed. This is all 1990s stuff.


Airbus envelope protection works because the “autopilot” is always engaged, in the usual flying mode, and you have auto throttle. Light GA has none of this, although I recall from another thread here that some SR22 installation does have the pitch servo always connected – ??

Shoreham EGKA, United Kingdom

All newer Cirrus airplanes with either the GFC700, the DFC100 or the DFC90 autopilot have envelope protection, although only the full Garmin Perspective installations have it on all the time. Those will automatically correct pitch or bank angle, even when hand flying.

With my DFC90 installation it will always warn but only actively intervene when the A/P is ON. In this case you can reduce the power to idle in cruise and the autopilot will always lower the nose at the right speed to avoid a stall, even in turns (“Envelope Protection Active” is what it announces then). This means that you can use it in case of engine failure, for example in HDG or NAV mode. You can also set the best glide speed in the IAS window.

Last Edited by at 20 Jul 08:48

Welcome to the 90es :-)

I do know what CAN is – my soon to arrive MSOX3034T even has a CAN protocol analysis mode… What I was getting at is that CAN is not necessary for the AP to monitor the flaps.

Shoreham EGKA, United Kingdom

No it’s not but it is much easier to add on stuff on a CAN architecture than to draw individual wires for everything you want to add on and find you’re SOL if there is no pin left on your RS232…

Yeah but this is GA, not VW or Merc or ….

CAN might well be used internally by some GA products. I vaguely recall some homebuilt products are using it. Garmin might be using it too, because it is “quite trendy” if you recruit people with an automotive background and it creates a lot of employment for software people. It’s also not a bad solution for interfacing to your own AP servos, even though it is pointless where you could just have an analog voltage. Real hardware engineers use I2C or SPI because they are much easier to debug and don’t require obscure (=potentially buggy) protocol stacks I have been hacking my VW over CAN to enable/disable certain features (with the usual bootleg VAG-COM stuff) and it is clearly immensely complicated. There is a lot of money being made on the back of automotive CAN…

Also a flap doesn’t have an RS232 output, or a CAN output, because it is just a piece of metal, but I am sure you knew that… It is far easier to connect a wire to some flap position sensing microswitch and feed that to the AP than to have a position sensor (containing a computer with a few hundred k of code) which the AP can interrogate over CAN to see where the flap is sitting. Simplicity is far better in this case…

Shoreham EGKA, United Kingdom

GA is for sure not either VW or Merc… how is the piece of metal feeding position information into the AP?

Why would you run 1x flap motor cabling, 1x flap indicator cabling and 1x autopilot cabling when you can run 1x cabling?

Last Edited by Shorrick_Mk2 at 20 Jul 10:07
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