1. Means processing a linearized rate output signal from the nonlinear output of a radio altimeter comprising, signal linearizing means receiving the output of said radio altimeter and providing a linearized radio altitude output signal, signal differentiating means receiving the output of said radio altimeter and providing a nonlinear radio altitude rate output signal, signal processing means receiving said linearized radio altitude signal and developing a two-level binary output signal with duty cycle proportional to said linearized radio altitude signal level between linearized radio altitude signal levels respectively indicative of defined nonlinear radio altimeter output levels corresponding to the extremes of the logarithmically varying segment of the output characteristic of said radio altimeter and including means to hold said binary level output signal at respective ones of said binary levels in response to the linearized radio altitude input levels exceeding and being less than said defined levels, signal amplifying means receiving said nonlinear radio altitude rate signal as input thereto and comprising gain changing means receiving and responsive to the output of said signal processing means to exhibit first and second discrete gain levels respectively in response to the respective binary levels of the output of said signal processing means, and the output of said signal amplifying means comprising said linearized rate output signal.