Airborne Weather Radar — Page 220, Lesson 208

Let's pick up with the rest of the airborne weather radar controls. We've already covered the main functions, so now I want to walk you through three specific features you'll find on the control unit: HOLD, TGT ALERT, and FAULT. First, HOLD. This is a display freeze function. Its purpose is to let you assess how a storm is moving. Here's the procedure: when you locate a storm, say at 100 nautical miles, you select HOLD and maintain a constant heading. The screen will then show HOLD and WX alternately — that's your cue that the display is frozen. After two or three minutes, you deselect HOLD. That brings back the live, current display, and you'll see the storm position shift from where it was held to where it actually is now. That movement, relative to the aircraft, tells you the storm's direction of travel. So HOLD is essentially a memory tool — it lets you compare a past snapshot against the present to see motion. Next, TGT ALERT. This works in conjunction with the WEA facility — the weather alert function. Its job is to alert you to a storm return of contour strength. Contour strength means the storm is intense enough that the radar is painting it as a contour — a solid, high-intensity return. When TGT ALERT is selected and there are no contouring clouds present, the screen shows a yellow T inside a red square, positioned at the top right of the display. That's the standby indication. But if a contouring cloud is detected within 60 to 160 nautical miles and within plus or minus 15 degrees of your heading, the symbol changes: instead of the static T, you get the yellow symbol TGT in a red square, flashing on and off once per second. So the flashing is your warning that a dangerous storm is within that range and angular sector ahead of you. Finally, FAULT. This is controlled by a fault monitoring circuit. If there's a power failure or a transmitter failure, the word FAULT flashes on the screen. That's your indication that the radar system itself has a problem — not a weather situation, but an equipment malfunction. The fault monitoring circuit continuously checks the system's health, and when something goes wrong with power or the transmitter, it flags it visually. So to summarize the three: HOLD freezes the display to track storm movement, TGT ALERT gives you a flashing warning when a contour-strength storm is within 60 to 160 NM and 15 degrees of heading, and FAULT alerts you to power or transmitter failure. Each one is a distinct safety feature on the radar control unit.