Eddie Sez:

So you know nothing about radar and want to learn. Let me suggest the following:

Need to know how all this fits with your chosen aircraft? Well if you are flying a G450 you are in luck:

What follows are quotes from the sources listed below, as well as my comments in blue.


Shadows

Thunderstorms and very tall mountains cast shadows, cities do not. To look for hazardous weather, turn the tilt to display lots of ground returns and look for a shadow. If you know there isn't a tall mountain there, you have spotted a thunderstorm.

Figure: Radar shadows, from Honeywell Radar Training Course, Part 4, Slide 5.

For this technique to work, the beam's width has to follow entirely within the structure of the storm's core area and the storm has to be deep enough to reduce the signal to a point it casts a shadow.

Figure: Radar beam must fall completely within thunderstorm, from Honeywell Radar Training Course, Part 4, Slide 9.

The larger the radar antenna, the larger a storm's shadow will appear, making it easier to spot. As a rule of thumb, for a 24-inch antenna, a storm will cast a shadow fifteen times the diameter of the storm's core. For example, if the storm casts a 150 nm shadow, the storm's core is likely to be around 10 nm in diameter.

Figure: Radar shadow caused by attenuation, from Honeywell Radar Training Course, Part 4, Slide 15.

You should leave the antenna gain in its calibrated mode for normal operations. If you suspect a radar shadow is just below your viewing threshold, reduce the gain so that all the display's colors are reduced. If the target is a thunderstorm (and not a city) the hiding shadow may present itself.

Figure: Radar gain tip, from Honeywell Radar Training Course, Part 4, Slide 20.


Procedure

The radar is calibrated to consider all reflected energy in the beam at each distance and present a color based on adding the various intensities:

Figure: Radar tilt management, from Honeywell Radar Training Course, Part 5, Slide 5.

The resulting tilt angle may result in a lot of ground clutter. This clutter can be reduced by raising the tilt so the bottom of the beam is at the bottom of the bright band, the core of the storm, which is typically around 8,000 feet.

Figure: Radar tilt management, from Honeywell Radar Training Course, Part 5, Slide 6.

Point the beam width to just include the bottom of the thunderstorm's core:

Figure: Radar tilt management, from Honeywell Radar Training Course, Part 5, Slide 12.

Figure: Radar tilt management, from Honeywell Radar Training Course, Part 5, Slide 12.


Tilt Management Procedure

Figure: Optimum tilt angle, from Honeywell Radar Training Course, Part 5, Slide 13.


Weather Examples

Stratus Rain

Stratus Rain is normally no higher than 15,000 feet and can spread for hundreds of miles; it is not particularly dangerous. Airborne radar cannot differentiate between light rain and the ground when at high altitude looking down. The reflectivity of the ground, especially if it is wet, greatly exceeds the water droplets. Once the aircraft has descended and is looking up at the rain, the problem goes away.

Figure: Stratus rain, from Honeywell Radar Training Course, Part 2, Slide 11.

Figure: Stratus rain summary, from Honeywell Radar Training Course, Part 6, Slide 7.

Ordinary Thunderstorm

The highest concentration of rain and rain-covered hail is in what meteorologists call the "bright band," typically located between 8,000 and 17,000 feet. This area offers the highest reflectivity, where the most information to radar is available. The beam must be pointed into this area to properly evaluate the storm's danger.

Figure: Thunderstorm, from Honeywell Radar Training Course, Part 2, Slide 9.

Super-cell Thunderstorm

A Super-Cell Thunderstorm is much wider than an ordinary thunderstorm and can often be identified by the radar shadow it creates. (The green arc above is ground clutter, but this ground clutter doesn't show behind the super-cell thunderstorm which obscures all radar returns from behind.)

Figure: Super-cell thunderstorm, from Honeywell Radar Training Course, Part 2, Slide 10.

Radar Example of Stratus Rain, Ordinary Thunderstorms, and Super-Cells

Figure:Weather target and how they are displayed ,from Honeywell Radar Training Course, Part 2, Slide 12.

Radar Example of a Blind Alley

Figure: Blind alley, from Honeywell Radar Training Course, Part 2, Slide 15.

Radar Example of a Thunderstorm Downwind

Figure: Deviate upwind, from Honeywell Radar Training Course, Part 2, Slide 16.

Normal Operations

Ground Operation

Be careful to avoid radiating in the direction of people or fueling operations.

The G450 radar defaults to "forced standby mode" when on the ground. Prior to takeoff, the forced standby mode can be over-ridden by pressing the STAB button four times in three seconds. The tilt should be aimed to just avoid ground clutter, typically around 8 degrees.

Initial Climb

Adjust the tilt to maximize the return from storms of interest and to minimize the ground clutter, typically around 4 degrees. Adjust the range to about 50 nm.

Cruise

Adjust the tilt to maximize the return from storms of interest and to reduce the ground clutter to the outer third of the display. This will normally be around 3 degrees around 18,000 feet and gradually decrease to about 0 degrees at 45,000 feet. Adjust the range to about 200 nm.

Descent

You may need to raise the tilt to compensate for the deck angle of the aircraft. Contrary to popular belief, there is no "auto" function on most radars, no automatic tilt compensation for aircraft pitch attitude. In the G450 Radar system, for example, the "A" denoted by tilt angles refers to "Altitude Compensated Tilt," which adjusts tilt for the selected range and aircraft altitude.

Approach and Landing

Adjust the tilt to maximize the return from storms of interest and to minimize the ground clutter; you are now looking up at potential thunderstorms. This will normally be around 9 degrees. Adjust the range to about 10 nm.


Book Notes

Portions of this page can be found in the book Flight Lessons 1: Basic Flight, Chapter 28.


References

Honeywell Airborne Weather Radar Training, Rev E, 12/09/02, Honeywell Inc. Commercial Flight Systems Group, Phoenix, AZ.

Honeywell Primus 880 Pilot's Guide, Pub. No. A28-1146-102-03, Revised January 2006, Honeywell International Inc. Commercial Electronic Systems, Glendale, AZ.