Some operators prefer to have both visual indication and aural altering of Decision Height from the radar altimeter system. The KRA-405B P/N 066-01153-0202 provides an audio output that can be connected direct to an open selection on an audio panel. Otherwise, for the KRA-405B P/N 066-01153-0101 an external sonalert can be installed for aural altering. P/N 038-00008-0001 is suggested and the KRA-405B installation manual shows detailed information on how to install it.