2 - NAV PAGES46Departure Phase - Defined as when all five of thefollowing conditions are met:• It has been determined that the aircraft was previ-ously “on-ground.”• The aircraft has a vertical velocity greater thanzero.• The aircraft has a ground speed greater than 35knots.• The aircraft has an altitude greater than 150 feetAGL and less than 1500 feet AGL.• The aircraft is within 15 NM of the departureairport.NOTE: There are additional factors beyond whatis outlined above that may alter the determinedTERRAIN flight phase.Nearest Airport Criteria & Terrain Phase of FlightChanges to the Nearest Airport Criteria Page affecthow the TERRAIN system performs. The nearest air-port list is used to derive the terrain destination airportwhen there is no loaded active flight plan or whendeviating from the active flight plan (whenever theterrain algorithms go into estimation mode). In turn,the nearest airport list is used to determine the terrainphase of flight. The terrain phase of flight dictatesthe Required Terrain Clearance (RTC) levels at whichForward Looking Terrain Avoidance (FLTA) alertingoccurs, as described later in the Forward LookingTerrain Avoidance section. Premature Descent Alerting(PDA) is also affected as described later in the PDAsection.Nearest Airport Criteria PageAs an example, if the pilot configures the unitto include only airports with runways 5000 feet orlonger, only these are added to the nearest airport list.The terrain phase of flight is affected in that all airportrunways under 5000 feet are NOT included in terraincalculations. During a cross-country flight with thisconfiguration, only airports runways 5000 feet orgreater cause the unit to go into Terminal or ApproachMode from En Route mode. If the pilot makes anemergency landing at an airport that did not show upin the nearest airport list, FLTA alerts would be issuedthroughout the descent.TERRAIN Destination AirportThe TERRAIN destination airport is considered tobe the next airport in the flight plan while adheringto the flight plan path. If no flight plan is entered, orif the aircraft is not adhering to the entered flight planpath, the terrain destination airport is estimated usingthe Nearest Airport Criteria as described in the sectionabove.Terrain Operation
