"Hi Janne. In my case I just forgot to connect a ESC/BSC ... the pixhawk doesn't have a supply voltage on its AUX outputs! After I supplied it, it worked, as described here:
http://ardupilot.org/plane/docs/common-servo.html

No, I don't use a skycat…"

"OK, I found it ... The output level on AUX1 is 3.3V and I guess my servos i was using, are 5V. I am lucky to have a oscilloscope to check it.
So everything is working as described on the wiki pages!"

"No one?

Other thing I came across. There is the parameter CH7_OPT which can be set to "Parachute Release" and the parameter RC7_FUNCTION which can be set to "Parachute" ... what's the difference?

Is CH7 the function for input (from the receiver)…"

"Sorry for my late reply. You are right, in this case you have to invert the directions for ailerons and rudder and then invert on the rc as well. It can be easily tested on the ground when switching to an auto mode and turn the plane. Then it should…"

"According to:
http://plane.ardupilot.com/wiki/arduplane-setup/first-time-apm-setu...
It must be one of the ELEVON_REVERSE, ELEVON_CH1_REVERSE or ELEVON_CH2_REVERSE parameter but I can't find them in the parameters of my plane.
I used qgroundcontrol…"

"I think that's exactly the procedure I have to walk through - I'll try this"

"Yes, that's exactly the behaviour that doesn't work the right way!
But wich parameter is responsible to reverse the aileron servos - elevator and rudder already work the right direction."

"It happens when switching from manual to auto flight mode when the plane is heading tot the first waypoint. And I think the ailerons are steering in the wrong directions as well, when setting the plane to ALTCTL mode and rolling it."

"Might this be the reason?
http://plane.ardupilot.com/wiki/flying/inverted-flight/

But we installed the firmware via QGroundControl and guess this feature isn't enabled by default. And when I download all parameters, there is no one called…"