I don't understand why/how a feed of IMU data (gyro + probably accelerometers) could over-ride a Doppler altimeter that "functioned properly"... Any aircraft th

I don't understand why/how a feed of IMU data (gyro + probably accelerometers) could over-ride a Doppler altimeter that "functioned properly"... Any aircraft that would use inertial data to determine altitude would be in very deep trouble on Earth as well. I don't get it.