Runway Field Clearance Floor (Rfcf) - Honeywell Bendix/King KGP 560 Pilot's Manual

Functions and Features
When the "Look-Ahead" function detects a terrain or obstacle threat
approximately one minute ahead of the aircraft, the voice alert "Caution
Terrain, Caution Terrain" (or "Caution Obstacle, Caution Obstacle") is
given, and a bright, solid yellow "threat area" is shown on the Terrain
Display. Should the aircraft flight path continue toward the threat area,
the alert message will repeat approximately every 7 seconds.
If the aircraft flight path approaches to within approximately 30 seconds
of a threat area, the voice message "Terrain Ahead" (or "Obstacle
Ahead") or optionally "Terrain Terrain, Pull Up" (or "Obstacle-Obstacle,
Pull Up") will be given continuously and the threat area on the Terrain
Display will be shown in a bright, solid red color.
In either case, when the pilot reacts and changes the aircraft flight path
to one that will safely avoid the detected threat area, the voice alerts will
cease and the threat area(s) shown on the Terrain Display will be
removed.

RUNWAY FIELD CLEARANCE FLOOR (RFCF)

The KGP 560/860 GA-EGPWS provides additional alerting protection for
situations where aircraft descend to an altitude that is too low consid-
ering the aircraft's distance from a known runway. This is called the
Runway Field Clearance Floor (RFCF).
NOTE: This alert function is ONLY active when the aircraft is within 5 nm
of a known runway in the system database.
Using the aircraft distance to a known runway and Geometric Altitude,
the system establishes a "floor" of protection below the aircraft.
Penetration of this floor will cause the yellow caution alert annunciator
lamp to illuminate, and the voice alert "Too Low, Too Low" to be heard.
If aircraft altitude continues to descend, the voice alert will be heard
again, and at an increasing frequency.
When the pilot reacts to the alert and climbs back above the RFCF for
the current distance from the known runway, the annunciator lamp will
extinguish and the voice alerts will cease.
The following figure is a graphical representation of the Runway Field
Clearance Floor in both the "TSO" and "optional alerting and warning
parameters outside the TSO" configurations.
16
Rev 5 Jul/2004
KGP 560/860 Pilot's Guide