Airborne weather radar (AWR) is used to provide pilots with information regarding weather ahead as well as navigation. Unlike most other systems, it requires interpretation by the pilot and its use is enhanced by the skill of the user.
The radar information can be displayed on a dedicated unit or shown (on modern aircraft) in combination with the aircraft route on the EFIS navigation display (ND).
Information on cloud formations or terrain features is displayed on the indicator’s screen as a range from the aircraft and a bearing relative to its heading. The presentation can be monochrome or, on modern systems, in the colours green, yellow, red and/or magenta. In the weather mode the colours represent the increasing variations in rainfall rate from light to very strong returns; magenta usually indicates the presence of turbulence associated with intense
rainfall. For ground mapping green indicates light ground returns, yellow medium ground returns and red heavy ground returns.
The airborne equipment comprises:
• Transmitter/receiver. (Figure 13.1)
• Antenna, which is stabilized in pitch and roll. (Figure 13.1)
• Indicator. (Figures 13.1, 13.2, 13.3 and 13.4)
• Control unit. (Figure 13.1)
The main functions of an AWR are to:
• detect the size of water droplets and hence deduce where the areas of turbulence are within the cloud.
• determine the height of cloud tops by tilting the radar beam up or down.
• map the terrain below the aircraft to provide navigational information and high ground avoidance.
• provide a position fix (range and bearing) from a prominent feature.