Reading pitch&roll information in mavilink protocol

i am trying to display the pitch and roll information in actual experimental plane of mine using flight controller(with an ardupilot firmware) and a external microcontroller which reads this information trough the mavilink protocol.
On the ground when i tilt the device it is working perfectly.
How ever in real flight it’s just not working…
Am i missing something here ? should the pitch and roll information in the mavilink are real data in flying conditions…?
I would appreciate very much any Help…!
Best regards,