Airborne Weather Radar — Page 220, Lesson 200

I want to walk you through the control unit of the airborne weather radar — the AWR — because this is the panel you'll actually be reaching for in the cockpit. Let's start with the big picture, then go control by control. First, the display itself. This is a monochrome AWR, meaning the screen shows a single colour — typically green — and the control unit I'm describing has range scales of 20, 50, and 150 nautical miles. So you can think of the radar picture as a map centred on your aircraft, and you choose how far out you want to look. Before we touch the controls, I want you to understand the weather signatures you're looking for on that screen, because the whole point of this radar is to detect hail. There are four classic shapes that indicate hail activity. The first is the U-shape — the radar return forms a letter U, and that's a strong sign of hail. The second is the finger — a narrow protrusion extending from the main weather return, again indicating hail. The third is the scalloped edge — the edge of the return isn't smooth, it's wavy or scalloped, and that also indicates hail. And the fourth is the hook — a curved extension at the end of the return, which is another classic hail signature. So when you see any of these four shapes — U, finger, scalloped edge, or hook — treat that cell as hail-bearing. Now let's get onto the control unit itself. There are three main controls: the power switch, the range switch, and the tilt control. The power switch. In the ON position, the system is energised, and the aerial — that's the antenna — is automatically stabilised in pitch and roll. What that means is the radar keeps its beam level relative to the horizon even if your aircraft is banking or pitching. Now here's a diagnostic clue: if you see a lopsided or asymmetric display, that probably indicates the stabilisation has failed. In that case, you switch to the STAB OFF position, and that locks the scanner to the pitch and roll axes of the aircraft — so the antenna now moves with the aircraft instead of staying horizon-stabilised. Next, the range switch. The STANDBY position holds the equipment in readiness during periods when the AWR is not required. This is a safety-critical position, and I want you to take this seriously. While you're on the ground, you must maintain STANDBY until you're certain that personnel and any reflecting objects — such as hangars — are not in the radar's transmitting sector. Why? Two reasons. The radiation can damage health, and the reflections from adjacent structures can damage the equipment. So never energise the transmitter on the ground with people or buildings in the beam. And note this: selecting the MAPPING beam produces the same hazards — so the same caution applies there. Now, in poor weather conditions, the procedure is to switch from STANDBY to the 0–20 NM scale as soon as the aircraft is clear of personnel and buildings, and check the weather conditions in the take-off direction. So you're using the short range to look ahead on departure. And the maximum practical range for weather and for navigation is in the region of 150 NM — that's the outer limit of what's useful. Finally, the tilt control. This enables the radar beam to be tilted from the horizontal within 15° up, marked with a plus, and 15° down, marked with a minus. In the horizontal plane, the antenna sweeps up to 90° either side of the nose — so a full 180° sweep across the front — though a sector of 60° on each side is generally sufficient for the role of weather depiction and navigation. Now here's the key operating logic for tilt. For ground mapping, the beam has to be tilted down — you want to see the surface. But to observe cloud formations, you raise the beam to reduce ground returns — you want to see the weather, not the ground clutter. And there's a subtlety due to the curvature of the earth. The tilt should be higher when the selected range increases, or when the aircraft descends to a lower altitude. Equally, the tilt setting should be lower when the selected range decreases, or when the aircraft climbs to a higher altitude. Think about why: at longer range, the earth curves away from you, so you need to tilt up to keep the beam on the weather; at lower altitude, you're closer to the ground, so again you tilt up to avoid ground returns. The reverse applies for shorter range and higher altitude. So to summarise the whole panel: power switch handles energising and stabilisation, with STAB OFF as the failure fallback; range switch handles STANDBY versus active transmission, with strict ground-safety rules; and tilt control shapes where the beam points vertically, with the earth's curvature dictating how you adjust it for range and altitude. That's the control unit. When you're ready, we can move on to the next part of the radar system.