A warning system for aircraft equipped with an autopilot system having a radio altitude hold (R/A HOLD) function and/or a barometric altitude hold (ALTITUDE HOLD) function monitors the R/A HOLD and ALTITUDE HOLD function control switches, as well as the touch-controlled steering (TCS) control to determine...http://www.google.co.uk/patents/US5585791?utm_source=gb-gplus-sharePatent US5585791 - GPWS autopilot monitor
