Garmin GDL 88 Series Pilots Guide - Page 19

Anonymous Mode, Air/Ground Determination

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3.4 Anonymous Mode The GDL 84/88 provides an Anonymous Mode which broadcasts a randomized ICAO address in the ADS-B Out message. The Anonymous Mode, when armed, replaces the Flight ID with a temporary randomized number for privacy while the position information is still provided. Anonymous mode is armed via a switch in the cockpit or via a control on the display integrated with the GDL 84/88. When a VFR squawk is present in the transponder and anonymous mode is selected, the GDL 84/88 operates in anonymous mode and no identifying information is provided in the ADS-B Out message. This mode will persist until the squawk code is changed or the Anonymous Mode control is turned off. Anonymous Mode is not available in aircraft with a Mode S transponder. 3.5 Air/Ground Determination If the GDL 84/88 is interfaced to a weight on wheels or squat switch, it will use that input to determine air/ground status. If the GDL 84/88 is not interfaced to a weight on wheels or squat switch, then air/ground status is based on GPS vertical velocity, track, and ground speed. For GDL 84/88 Installations in helicopters the transmitted air/ground state is as follows: • If a radar altimeter, Height Above Terrain (from an interfaced navigator), or Height Above Airport (from interfaced navigator) is interfaced to the GDL 84/88, then, when the helicopter has less than 15 knots ground speed and less 25 ft above ground, then the status is ON GROUND. • If those inputs are not available for a GDL 84 or GDL 88, then the helicopter transmitted state is ON GROUND only if the collective is fully down for at least 5 seconds. The helicopter will transmit IN AIR when in a stationary hover at the surface. This additional functionality is important because most alerting systems do not provide Traffic Alerts for on-ground aircraft. This capability reduces nuisance alerts when helicopters are operating near the surface at an airport. 190-01122-03 Rev. E Garmin GDL 84/88 ADS-B Transceiver Pilot's Guide 3-3

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3-3
190-01122-03
Rev. E
Garmin GDL 84/88 ADS-B Transceiver Pilot’s Guide
3.4
Anonymous Mode
The GDL 84/88 provides an Anonymous Mode which broadcasts a randomized
ICAO address in the ADS-B Out message. The Anonymous Mode, when armed,
replaces the Flight ID with a temporary randomized number for privacy while the
position information is still provided. Anonymous mode is armed via a switch in
the cockpit or via a control on the display integrated with the GDL 84/88. When
a VFR squawk is present in the transponder and anonymous mode is selected,
the GDL 84/88 operates in anonymous mode and no identifying information is
provided in the ADS-B Out message. This mode will persist until the squawk code
is changed or the Anonymous Mode control is turned off.
Anonymous Mode is not available in aircraft with a Mode S transponder.
3.5
Air/Ground Determination
If the GDL 84/88 is interfaced to a weight on wheels or squat switch, it will use
that input to determine air/ground status. If the GDL 84/88 is not interfaced to a
weight on wheels or squat switch, then air/ground status is based on GPS vertical
velocity, track, and ground speed.
For GDL 84/88 Installations in helicopters the transmitted air/ground state is
as follows:
• If a radar altimeter, Height Above Terrain (from an interfaced navigator),
or Height Above Airport (from interfaced navigator) is interfaced to the
GDL 84/88, then, when the helicopter has less than 15 knots ground
speed and less 25 ft above ground, then the status is ON GROUND.
• If those inputs are not available for a GDL 84 or GDL 88, then the
helicopter transmitted state is ON GROUND only if the collective is fully
down for at least 5 seconds. The helicopter will transmit IN AIR when in
a stationary hover at the surface.
This additional functionality is important because most alerting systems do
not provide Traffic Alerts for on-ground aircraft. This capability reduces nuisance
alerts when helicopters are operating near the surface at an airport.