Methods and apparatus for vertical motion detection of objects, such as aircraft. In one embodiment, a method comprises receiving altitude data for an object, determining a residual of a lag function, wherein the lag function comprises a moving average of the altitude data for the object, and wherein the residual corresponds to a difference between a value for the lag function and the object altitude data at a given time such that the residual grows in magnitude over time in response to the object transitioning from level flight to vertical motion, detecting vertical motion of the object by comparing a sum of data derived from the residuals against a threshold value, and outputting a vertical motion indicator after detecting the vertical motion of the object.