Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 76
6.3.1.3 Alert Envelopes
The TCF alert envelope is a circular band centered over the selected runway. Figures 6.3.1.3-1 and 6.3.1.3-2 illustrate the
shape of the TCF alert envelope.
FIGURE 6.3.1.3-1: TCF ALERT ENVELOPE COMPONENTS
1/2 Runway Length
Envelope Bias Factor
TCF Alert Envelope
FIGURE 6.3.1.3-2: TCF ALERT ENVELOPE CUT-AWAY VIEW
Terrain
4NM 12NM 15NM
400' AGL
700' AGL
Terrain
*
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 radius of the envelope is modulated based on the runway length and an envelope bias factor (k).
Runway length will vary from one runway to the next, and the envelope bias factor is typically 0.35 nm to 1 nm (varying with
position accuracy). Figure 6.3.1.3-2 illustrates a cutaway “slice” of the alert envelope. The outer alert envelope boundary
extends to infinity, or until it meets the outer alert envelope boundary of another runway.
The TCF curve is limited to a minimum value of 245 feet when it is determined that the aircraft is to the side of the runway.
This is shown in the central portion of Figure 6.3.1.3-2 and as a shaded area in Figures 6.3.1.3-3 and 6.3.1.3-4. This feature
provides improved alerting when landing to the side of the runway.
Figure 6.3.1.3-5 is a view of the TCF protection area when aligned with the runway.