400/500 Series Garmin Optional Displays

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Section 2
TERRAIN Operation
Figure 2-8: Nearest Airport Criteria Page
•Departure Phase – Defined as when all five of the following conditions are met:
(1) It has been determined that the aircraft was previously “on-ground”.
(2) The aircraft has a vertical velocity greater than zero.
(3) The aircraft has a groundspeed greater than 35 knots.
(4) The aircraft has an altitude greater than 150’ AGL and less than 1500’ AGL.
(5) The aircraft is within 15 NM of the departure airport.
NOTE: There are additional factors beyond what is outlined above that may alter the
determined TERRAIN flight phase.
Nearest Airport Criteria & TERRAIN Phase of Flight
Changes to the Nearest Airport Criteria Page (Figure 2-8) affect how the TERRAIN system performs.
The nearest airport list is used to derive the terrain destination airport when there is no loaded active flight
plan or when deviating from the active flight plan (whenever the terrain algorithms go into estimation
mode). In turn, the nearest airport list is used to determine the terrain phase of flight. The terrain phase
of flight dictates the Required Terrain Clearance (RTC) levels at which Forward Looking Terrain Avoidance
(FLTA) alerting occurs, as described on page 40. PDA alerting is also affected as described on page 41.
As an example, if the pilot configures the unit to include only airports with runways 5000’ or longer,
only these are added to the nearest airport list. The terrain phase of flight is affected in that all airport
runways under 5000’ are NOT included in terrain calculations. During a cross-country flight with this
configuration, only airports runways 5000’ or greater cause the unit to go into Terminal or Approach Mode
from Enroute mode. If the pilot makes an emergency landing at an airport that did not show up in the
nearest airport list, FLTA alerts would be issued throughout the descent.
TERRAIN Destination Airport
The TERRAIN destination airport is considered to be the next airport in the flight plan while adhering
to the flight plan path. If no flight plan is entered, or if the aircraft is not adhering to the entered flight
plan path, the terrain destination airport is estimated using the Nearest Airport Criteria as described in the
section above.