Garmin International
1200 E. 151
st
Street Olathe, KS 66062
USA
ROTORCRAFT FLIGHT MANUAL SUPPLEMENT
for STC SR02123SE
GARMIN GDL 84H/88H ADS-B TRANSCEIVER
190-01310-J1 Rev. 1 Page 13 of 15
Pressure Altitude Broadcast Inhibit
For rotorcraft with an interfaced Garmin GTX 33/330/32/327 or SL 70
transponder the broadcast of pressure altitude is controlled by the transponder
mode. Turning the transponder to ALT will also broadcast pressure altitude in
the ADS-B output. Turning the transponder to ON will inhibit pressure altitude
from being broadcast.
For rotorcraft without a Garmin GTX 33/330/32/327 or SL 70 transponder
pressure altitude broadcast is controlled via a separate switch or interfaced GNS
or GTN display.
Traffic Sources and Alerting
The GDL 84H/88H is capable of receiving ADS-B, ADS-R, and TIS-B traffic
reports in order to track traffic around the rotorcraft and provide alerts to the
flight crew to aid in visual acquisition and avoidance.
Traffic alerting is provided via a visual annunciator and audio callouts for these
alerts.
Rotorcraft which have a Radar Altimeter OR GNS or GTN display interfaced to
the GDL 84H/88H will truncate traffic aural alerts to not include bearing,
distance, and relative altitude information when less than 200 ft above the
surface. Additionally, these GDL 84H/88H will reduce the protected volume
around these rotorcraft when operating below 200 ft above the surface and less
than 60 kts groundspeed to minimize nuisance alerts in the airport area while
still providing traffic alerts on other eligible ADS-B OUT equipped aircraft.
Aircraft which are ADS-B participants transmitting on the 1090 MHz band do
not transmit altitude while in the on ground state and thus will not generate
traffic alerts until becoming airborne.
Due to some aircraft not being required to equip for ADS-B Out, as well as the
nature of TIS-B, its service volumes, not all traffic will be tracked by the GDL
84H/88H. This is much like an active traffic system which does not track non-
transponder equipped aircraft. The flight crew must use “see and avoid”
procedures to visually acquire and avoid other aircraft.
On Scene Mode (OSM)
Rotorcraft which have a GTN display interfaced to the GDL 88H have the
ability to use On Scene Mode (OSM). OSM reduces the protected volume
around the rotorcraft for alerts that would be produced by other ADS-B
equipped helicopters. OSM must turned ON and OFF by the pilot using the