Systems Guide

A318/A319/A320/A321
Professional
SYSTEMS
Systems guide
Vol
4
04-03-61
11 July 2018
AUTOTUNE ILS
An ILS is autotuned when the departure runway has a ILS (during PREFLIGHT AND TAKE OFF mode) and
when the F-PLN approach mode has an ILS in all other modes.
PASSENGER SIGNS
The passenger (previously no smoking) signs should be left ON during all operational flights. The seatbelt
sign behavior is semi-automated when in AUTO and the seatbelts sign will be lit when the aircraft is below
10,000 feet. Any time the indication for the passengers changes a chime is played in the cabin.
WEATHER RADAR
The Collins WXR (weather radar) detects precipitations by means of a high frequency radar. The radar
beam reflects of rain drops or hail and is received by the system. The radar returns are then displayed in a
calibrated gain color system. When the radar beam hits the ground (or other solid objects) it is also
returned. The Collins WXR can eliminate ground clutter to provide a clearer image. However, the Ground
Mapping option does allow the user to scan the ground and pick up coastlines and other important
ground features.
The fully automated multiscan mode sets the gain and tilt automatic to the ideal settings for each stage of
the flight, reducing pilot workload. Multiscan operates the weather radar as a highly experienced would
do manual.
The pilot is advised to keep in mind that at the cold
top of clouds the water is mostly in ice crystals and
super cooled water. These are not reflected by the
radar very effectively. Scanning a cloud from top to
bottom using the manual scan will show that as
reflections will increase near the bottom of the cloud
where all the precipitation is in the form of liquid
water and the density of droplets highest.
As radar beams travel in a straight line the curvature
of the earth is important. Low clouds can be invisible
at a distance because they are hidden by the
curvature of the surface even though they are in
range. In multiscan mode the radar is able to skim
the radar horizon (tilting the beam so it remains just
above the horizon). Keep in mind that over 320 NM
the curvature of the earth causes the earth’s surface
to move down approximately 65,000 feet. So, if the
aircraft is at 25,000 feet the earth’s surface is about
90,000 feet below the aircraft 320 NM in front of the aircraft. The antenna is stabilized up a 45-degree
bank, meaning the radar sweep will be level with the horizon up to 45 degrees. It is also stabilized for
pitch.
AUTO MULTISCAN MODE