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4-7
190-01122-03 Rev. A
GDL 88 ADS-B Transceiver Pilot’s Guide
Radar Altitude
(RA) or Height
Above Terrain
(HAT)
(if Available)
GPS Phase
of Flight
RA, HAT, and
GPS Flight
Phase Not
Available
OR
GPS
Phase of
Flight Not
Approach or
Terminal
Sensitivity
Level
Look-
Ahead
Time(s)
Vertical
Threshold
for Alarm
(feet)
Minimum
Protected
Volume
(NM)
Up to 1000
(RA or HAT)
Approach N/A 2 20 850 0.20
1000-2350
(RA or HAT)
Terminal N/A 3 25 850 0.20
2350-5000
(Geodetic)
Below
5000
(Geodetic)
4 30 850 0.35
5000-10,000
(Geodetic)
5000-
10,000
(Geodetic)
5 40 850 0.55
10,000-
20,000
(Geodetic)
10,000-
20,000
(Geodetic)
6 45 850 0.80
20,000-
42,000
(Geodetic)
20,000-
42,000
(Geodetic)
7 48 850 1.10
Above 42,000
(Geodetic)
Above
42,000
(Geodetic)
8 48 1200 1.10
Table 4-2 Traffic Alert Functionality