Shadows always point directly away from the antenna. They have a fea-thered edge, as in the photo, and they continue outward as far as ground re-turns can be painted. (If the sides of a shadow come together in the distance, you are above the object casting it.)
Radar shadows are caused by a weather system so dense that radar en-ergy cannot penetrate it just as a shad-ow from a flashlight is caused by an ob-ject so dense that light is not able to penetrate it).
Notice in the photo that energy is penetrating the left side of the storm; it cannot penetrate the right side.
The rule is, never, never, ever contin-ue toward a radar shadow. Failure to recognize a shadow and abide by the rule is the cause of 90 percent of con-vective weather accidents. Eastern Air-lines Flight 66 crashed in a shadow at JFK in 1975; Southern's Flight 242 crashed in a shadow at New Hope, Georgia in 1977; Air Wisconsin crashed in a shadow northeast of Omaha in 1980; Pan American crashed in a shad-ow on takeoff at New Orleans in 1982; USAir crashed in a shadow at Detroit in 1984; Delta Airlines Flight 191 crashed in a shadow at DEW in 1985; a corpo-rate Westwind crashed near several shadows in 1986.
Evidence is abundant that airplanes cannot fly through weather that casts a shadow. Rainfall rates in a shadow -producing storm frequently exceed the certification limits of the aircraft and engines. In addition, shadowing storms will contain microbursts, downbursts, large hail, extreme turbulence and very possibly, tornadoes. A storm casting a shadow can be identified with tilt up, but the clues are subtle and easily misread. With the SAP technique they can-not be missed. Those who know how to identify and read such indications are safe pilots; those who don't may as well turn off their radar. It's useless to them. (By the way, don't rely on the gimmicks of some newer radars that purport to identify shadows but often do not indicate a shadow where there is one. Put your tilt down and watch for the real shadows.)
In these few pages we have barely exposed the tip of an iceberg. We've touched on only two of hundreds of techniques, shortcuts and radar facts that can never be discovered in years of self-education. We hope that the NTSB will have second thoughts on their tadt agreement with the statement, .... .with any airborne radar device, written instructions and classroom academics are highly inadequate."
Meanwhile, don't let that attitude be the cause of your accident. Practice the TIP, REP, TUT and SAP techniques until they become second nature with you. Then steer far, far away from all radar shadows.
Those Confusing Side Lobes
The fundamental truth in under-standing tilt management is that ra-dar detects and displays only those objects that fall within the limited area of the three degree to 1 degree conical beam. Objects not "Illuminated" by the finite dimensions of the beam are not detected.
But for every rule there is an ex-ception. If the antenna installation is poorly engineered or if the ra-dome is imperfect, ghost images appear on the indicator. Several weather echoes can be seen in the accompanying photograph. The one at 12 o'clock and two nautical miles, however, is not weather. It's a false echo.
False echoes are commonly re-ferred to as "side lobe returns," or simply as side lobes, although in reality they are caused by refracted energy from the main beam. Metal objects in the radome cavity, water trapped In the honeycomb of the radome, a metallic paint strip. around the nose or one of those horrible plastic nose caps can gen-erate side lobe returns.
The cause should be corrected by taking the aircraft to a first-class radome repair shop, but almost no one bothers, so pilots must learn to live with false echoes.
In some instances a spear of refracted energy points downward, bounces off the ground and shows up as an echo at 12 o'clock. No matter where you place the tilt, there is the echo at 12 o'clock. In other instances the spear points to the side so that you see a side-lobe return, also at 12 o'clock, only when flying abeam a storm.
In still other instances, you see no side lobe return when your ra-dome is dry; you see one only when your radome is wet or has Ice on it. Whenever you're in weather, you always have a false, contouring storm at 12 o'clock, never more than five or six miles distant.
A necessary radar skill is learn-ing to recognize and ignore side lobe returns. There are several ways to identify them. First, just observe your radar on clear days. Ex-ecute TIP and if you see an echo, it's a side lobe. Mark it in your mind as something to ignore.
If you see side lobe returns only when in weather, however, identify-ing them gets a little trickier. One clue is movement. An echo that you cannot catch up to is a side lobe re-turn because storms never move as fast as an airplane flies. An ex-ception (there's that exception again) is when you descend. A side lobe caused by energy spilling off the antenna and pointed straight down will appear at a range rough-ly equal to aircraft altitude agl. Therefore, when you're descend-ing or flying toward rising terrain, it will appear that you're overtaking a side lobe-which is something else you must observe on several flights and learn to ignore.
If all else fails, select the 50-nm range (or as close to 50 nm as pos-sible), run your tilt down until you have a solid ground paint from 10 or 15 nm outward, then back way off counterclockwise on your gain control. If a shadow appears be-hind the suspect echo, it's real; if not, it's a side lobe because side lobes do not cast shadows.
Business &Commercial Aviation / June 1987
Antenna Tilt