Question

When are airplanes in motion

Answer 1

When they are taxing around. Airplanes fly do to lift.

Answer 2

Motion is always relative to something.

-- Relative to the moon, an airplane is ALWAYS in motion.

-- Relative to the ground, an airplane is in motion when it's taxiing or flying.

-- Relative to a bag of peanuts in its own galley, an airplane is NEVER in motion.