Another observation - I was on the gate, zero speed, engaged parking brakes, fine weather with zero wind and /fdm/jsbsim/velocities/v-down-fps oscilated from -5 to +4 fps. Where is truth ???
I can't confirm this at all - on the ground I see any of v-down, v-north and v-east < 1e-7, which is consistent with residual oscillations in the ground interactions.