Weather Radar

What Is Weather Radar?

Airborne weather radar is a forward-looking radar system mounted in the aircraft's nose radome that transmits microwave pulses and analyzes reflections from precipitation particles — rain, hail, and wet snow. By measuring the intensity of returned signals, the radar maps precipitation density in the aircraft's flight path, allowing pilots to detect and circumnavigate storm cells, embedded cumulonimbus, and zones of potential turbulence.

How It Works

Weather radar operates in the X-band (9.3–9.5 GHz) or C-band (5.4 GHz). A mechanically or electronically scanned antenna sweeps horizontally in an arc (typically ±90°) and can be tilted vertically to sample different altitudes. Returned signals are color-coded by intensity:

• Black/Green: Clear or light rain — typically safe to fly through
• Yellow: Moderate precipitation — caution advised
• Red: Heavy rain, high reflectivity — avoid
• Magenta/White (on some systems): Extreme precipitation or hail — always avoid

Modern systems like the Honeywell IntuVue RDR-4000 or Collins WXR-2100 use 3D volumetric scanning, automatically building a full 3D weather picture without pilots manually adjusting tilt. Predictive Wind Shear (PWS) mode detects the Doppler signature of wind shear in the vicinity of the airport, issuing alerts during approach. Turbulence detection modes use Doppler processing to identify velocity variance in precipitation-free air.

Evolution and Modern Systems

Airborne weather radar entered commercial aviation in the 1950s. Early systems were analog and required constant manual tilt management. Digital processing in the 1980s brought automatic gain control and better clutter rejection. Flat-panel phased-array antennas — used on the 787 — eliminate mechanical scanning for faster updates and improved reliability. Ground-based weather data can now be overlaid on the glass cockpit moving map via datalink (SiriusXM Aviation, FIS-B), complementing the onboard radar.

Regulatory Requirements

FAA FAR 121.357 mandates airborne weather radar on turbine-powered large aircraft used in air carrier operations. Aircraft must not penetrate areas showing red or magenta returns. Operators must have procedures for weather radar interpretation in their Operations Specifications. Predictive Wind Shear systems, when installed, must provide alerts no later than 3 nautical miles from the wind shear event during approach and departure. Radar systems must be tested for radiation hazards (no personnel within the beam when operating on the ground).