Horizontal Alarm Limits - Garmin GNC 355 Pilot's Manual

CDI scale is set to "Auto" (default). At the default setting, the scale sets to
2.0 nm during the en route phase of flight.
Aircraft is within 31 nm of the destination airport (i.e., terminal area).
The scale linearly ramps down to 1.0 nm over a distance of 1 nm.
Aircraft is leaving the departure airport. The scale is set to 1.0 nm once the
aircraft is over 30 nm from the departure airport. It begins to gradually ramp up to
2 nm when the flight phase changes from terminal (TERM) to en route (ENR).
During GPS approach operations, the scale gradually transitions down to an angular
scale.
Aircraft is 2.0 nm before the final approach fix. Scaling tightens from 1.0 nm to
the angular full-scale deflection defined for the approach (typically 2.0º).
Selecting a lower value (0.3 nm or 1.0 nm) prevents the selection of higher scale
settings during ANY phase of flight. Example: If you select 1.0 nm, the unit uses
this setting for en route and terminal phases, and ramps down further during
approach.

Horizontal Alarm Limits

Horizontal alarm limits (HAL) are used to compare against GPS position integrity.
These protection limits follow the CDI scale, unless the corresponding flight phase
requires a lower HAL. For example, the selected scale setting is 1.0 nm, but full-scale
deflection during approach still follows the approach scale setting (0.30 nm).
FLIGHT
PHASE
Approach
Terminal
En Route
Oceanic
190-02488-01 Rev. B
CDI SCALE
0.30 nm or Auto
1.00 nm or Auto
2.00 nm or Auto
Auto
Pilot's Guide
Get Started
HORIZONTAL
ALARM LIMIT
0.30 nm
1.00 nm
2.00 nm
2.00 nm
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