Navdata from AR Drone 2.0

I’m currently receiving data from navdata_demo based on AR DRONE 2.0. I’m curious about which sensors and how to calculate the navdata_demo.phi, navdata_demo.psi and navdata_demo.theta. I have tried the transformation which calculates accelermeter reading ax, ay and az to rotation angle but the results are wrong.
I’ll be appreciate if somebody can help.