Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 75
6.3 Terrain Clearance Floor
Revision History
Effectivity
Date - Modified By Description of the Updates App. Cfg.
29-NOV-99 Peter Bateman Initial release and entry into PVCS -001 -001
24-MAY-00 Susie Wright SCR 4942: General document. -003 -003
06-JUN-00 – Susie Wright Document only change – Deleted proprietary note from footer. -003 -003
The Terrain Clearance Floor (TCF) alert function adds an additional element of protection to the standard Ground Proximity
Warning System. It creates an increasing terrain clearance envelope around the airport runway to provide CFIT protection
against situations where Mode 4 provides limited or no protection. TCF alerts are based on current aircraft location from
GPS, destination runway center point position (from the terrain database) and radio altitude. TCF is active during takeoff,
cruise and final approach. This alert mode complements the existing Mode 4 protection by providing an alert based on
insufficient terrain clearance even when in landing configuration. Alerts for TCF illuminate GPWS cockpit lamps and
produce aural messages.
The TCF function has been enhanced with a Runway Field Clearance Floor (RFCF) alert function based on current aircraft
location, destination runway center point position and height (MSL, not AGL) above destination runway.
When an aircraft penetrates either the TCF or the RFCF alert envelope the aural message “Too Low Terrain” will occur.
This aural message will occur once when initial envelope penetration occurs, and one time thereafter for each 20%
degradation in either altitude (AGL) or altitude (MSL) depending on which envelope was violated (TCF or RFCF
respectively). At the same time the appropriate GPWS alert lamps will illuminate. The lamps will remain on until the alert
envelope is exited.
6.3.1 TCF System Requirements
6.3.1.1 System Inputs
Table 6.3.1.1-1 lists the inputs and internal database items used with the TCF/RFCF function:
TABLE 6.3.1.1-1: TCF INPUTS
Parameter Source of Data
Radio Altitude External: Radio Altimeter (AGL)
Altitude External: Geometric Altitude (MSL)
Latitude External or Internal: GPS
Longitude External or Internal: GPS
FMS/IRS Update Discrete External for inertial based position
Runway Center Latitude Internal: Database
Runway Center Longitude Internal: Database
Runway Elevation Internal: Database
Alert Envelope Parameters Internal: Database
1/2 Runway Length Internal: Database
System Error Factor Internal: Database
6.3.1.2 Runway Database
The runway database consists of data records containing the position of airport runway center points along with 1/2 the
runway length. The database includes all runways in the region(s) loaded greater than or equal to 2000 feet in length. The
process of generating this database will be certified and will include an end check that validates that the data was not
corrupted in the translation process. This database can be updated without affecting the customer certified system part
number.
The design of the database and related software is such that additional runway records can be added in the future without
altering code. The database provides a means of accessing the records of runways closest to the current aircraft position.