no changes of vx of Navdata shows -0.0

[Yingxiu-Chang]

Hi,
I tried to use the navdata especially the vx, vy and vz. However, only the vz=-0.0 is not changed during flight as the attached image.
Could you please help me with it?
Thank you
Hugh

[Yingxiu-Chang]

Title is wrong, no changes of vz