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CONSIDERATIONS FOR SETTING
SHIELD RADIUS
Shield radius settings should be optimized (see Setup,
Appendix 1). If the shield radius is set too high, extraneous
alerts will be sounded from aircraft that are no threat. If set
to an excessively small value, warning time is compromised.
Use minimum values that provide adequate warning time.
Studies have shown that, given an alert, a minimum of ten
seconds warning time is practical. During the ten second
warning, the pilot first interprets the displayed data to
determine the altitude difference. An immediate reaction is
necessary only if this difference is zero or small. Two
aircraft converging at 540 knots will cover a distance of 1.5
NM in 10 seconds. Below 10,000 feet, it is unlikely that the
converging speed between two aircraft would exceed this
value. With the radius set at 1.5 iNM, the warning time for
threat aircraft would likely exceed ten seconds. A radius of
1.5 iNM would generally be adequate for standard
conditions, with a larger radius for Enroute and a smaller
radius for Terminal Mode.
The shield size is the pilot’s decision.
CONSIDERATIONS FOR SETTING
SHIELD HEIGHT
Two aircraft converging in altitude at 2400 feet per minute
will change altitude by 400 feet in ten seconds. A ±1,000-
foot shield height can be used in standard conditions. In
terminal areas where climb and descent rates are usually
slower, the limits could be narrowed, and then expanded for
enroute flight. When the shield around the host aircraft is
thin, extraneous alerts can be practically eliminated, while
maintaining good shielding against threats.
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