(c)
Alert Envelope The TCF alert envelope is a circular band centered over the nearest runway.
R (Ref. Fig. 024)
R 1EFF : 215-228, 301-302, 1 34-48-00Page A42 1 1 Config-1 Aug 01/05 1 1 1CES 1
Enhanced GPWS - TCF Alert Envelope R Figure 024
R 1EFF : ALL 1 34-48-00Page A43 1 1 Config-1 Aug 01/05 1 1 1CES 1 The distance from the runway center to the inner envelope edge is equal to 1/2 the runway length plus the envelope bias factor. Thus the inner and outer radius of the envelope are modulated based on the runway length and envelope bias factor. Runway length varies from one runway to the next, and the envelope bias factor is typically 1/2 NM to 2 NM and varies with position accuracy. The outer alert envelope boundary extends to infinity, or until it meets the outer alert envelope boundary of another runway. The alert is inhibited below radio altitude of 30 ft. This cutoff value was chosen to match the current Mode 4 lower cutoff value.
(d) System Outputs When an aircraft penetrates the TCF alert envelope the following aural message occurs: TOO LOW TERRAIN. This aural message occurs once when initial envelope penetration occurs, and one time thereafter for each 20 per cent degradation in radio altitude. At the same time the PULL UP legend of pushbutton switches 4WZ and 5WZ comes on. The legends remain on until the alert envelope is exited.
(3)
Not Applicable
(4)
Not Applicable
**ON A/C 001-049, 051-099, 101-105, 151-199, 201-214,
(2) Terrain Clearance Floor (TCF) The Terrain Clearance Floor (TCF) alert function adds an additional element of protection to the standard GPWS. It creates an increasing terrain clearance envelope around the airport runway to provide protection against Controlled Flight Into Terrain (CFIT) situations beyond that which is currently provided. TCF alerts are based on current aircraft location, nearest runway center point position 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.
(a) System inputs The following table lists the inputs required to allow implementation of the TCF function:
R 1EFF : 001-049, 051-099, 101-105, 151-199, 1 34-48-00Page A44 1201-228, 301-302, 1Config-1 Aug 01/05 1 1 1CES 1 -------------------------------------------------------------------------------| Input | Source | -------------------------------------------------------------------------------| Radio Altitude | External: Radio Altimeter | |----------------------------------|------------------------------------------| | Latitude | External: FMS | |----------------------------------|------------------------------------------| | Longitude | External: FMS | |----------------------------------|------------------------------------------| | Runway Center Latitude | Internal: data base | |----------------------------------|------------------------------------------| | Runway Center Longitude | Internal: data base | |----------------------------------|------------------------------------------| | Navigation mode | FMS | |----------------------------------|------------------------------------------| | Alert Envelope Parameters | Internal: data base | |----------------------------------|------------------------------------------| | 1/2 Runway Length | Internal: data base | |----------------------------------|------------------------------------------| | System Error Factor | Internal: data base | -------------------------------------------------------------------------------
(b)
Runway Data Base The TCF runway data base consists of data records containing the position of airport runway center points along with 1/2 the runway length. The data base includes all hard surface runways in the world greater than or equal to 3500 ft. in length. The process of generating this data base is certified and includes an end check that validates that the data was not corrupted in the translation process. This data base can be updated without affecting the customer certified system part number. The design of the data base and related software is such that additional runway records can be added in the future without altering the code. The data base provides a means of accessing the runway record of the runway closest to the current aircraft position.
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