Systems and methods are disclosed that include fault monitoring for a radar altitude device. Fault monitoring is performed by receiving first altitude data from the radar altitude device, receiving second altitude data from a second altitude measuring device, receiving terrain data from a terrain database, determining a fault condition threshold adaptively based on the terrain data, determining whether the radar altitude device is exhibiting a fault condition based on the first and second altitude data and the fault condition threshold, and outputting an indication of the fault condition based on the determination of whether the radar altitude device is exhibiting the fault condition.