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CFI Instrument Practical Test Standards, FAA-S-8081-9B, June 2001

II. Technical Subject Areas

A. Aircraft Flight Instruments and Navigation Equipment

    3. Anti-ice/deicing and weather detection equipment and their operating characteristics
      f. Radar/lightning detection system
        1) Wx-500 Stormscope Series II Weather Mapping Sensor (Stormscope)
          a) Description
            i) Detects thunderstorm-associated electrical discharges within a 200 MN radius an sends information to a separate multifunction display (MFD) that depicts the location of these thunderstorms
            ii) Includes a combined crossed-loop and sense antenna mounted on the outside surface of the aricraft and a processor that converts discharge signals into range and bearing data and updates the MFD with this information every 2 seconds
            iii) Data types displayed
            • Cell data most useful during periods of heavy electrical discharge activity
            • Strike data most useful during light electrical activity; may show newly building thunderstorm before cell display
            • Strike rate (approximate strikes per minute) helps pilot determine if cells are building or decaying
          b) Compared to weather radar
            i) Radar transmits UHF radio waves and receives echoes from water droplets while Stormscope receives atmospheric electrical discharges
            ii) Cumulus stage of thunderstorm
            • Unlikely to appear on radar
            • Generally will be detected by Stormscope by light but increasing cluster of discharge points
            iii) Radar, but not Stormscope, subject to attenuation, so may not see another thunderstorm behind a thunderstorm
          c) Operation with Garmin GNS 530
            i) Data displayed and unit operated via GNS 530 MFD
            ii) Runs self test automatically on start up
            iii) Performs continuous self test several times each minute
            iv) Storm data displayed on Map Page only if aircraft heading data is provided to the GNS 530 (e.g., via HSI)
            v) Otherwise, storm data is available on third Nav Page, the Traffic/Weather Page
            • Press MENU to select Weather? (or Traffic Screen)
            • Press then rotate small right knob to select Cell or Strike mode
            • Press MENU to select 120° or 360° viewing angle
            • Press MENU and select Clear Storm Data?
              • After heading change (if heading information not availble to GNS 530)
              • Periodically to help determine if storm is dissipating or building (discharge points will reappear faster and in larger numbers)
          d) Interpretation of Stromscope data on the GNS 530 Weather Page
            i) Clusters of two or more discharge points that reappear after clearing in the strike display mode indicate thunderstorm activity
            ii) In cell display mode even a single discharge point may represent a thunderstorm
            iii) In western United States a severe thunderstorm may have only a few discharge points
            iv) Pilots should "avoid by at least 20 miles any thunderstorm identified as severe or giving an intense radar echo." (Airman's Information Manual)
            v) Radial spread artifact
            • Triangular-shaped stream of discharge points between aircraft and cluster of discharge points in strike mode
            • Reduce range and/or switch to cell mode to reduce radial spread
            vi) Randomly scattered discharge points
            • More likely in strike mode, may indicate instability in cumulus clouds or developing or dissipating thunderstorm
            • Watch for developing clusters (thunderstorms)
            vii) Cluster and splattering in 25 NM range
            • Splattering due to discharge within 3 to 5 NM from aircraft too close to thunderstorm
            • Fly away from main cluster
            • Avoid any grouping of discharges within 25 NM
            viii) Discharge points off nose just inside 200 NM range
            • May be strong thunderstorm just beyond 200 NM, or
            • May be discharges arriving via atmospheric skip from distant thunderstorm well beyond 200 NM
            ix) Line of discharge points may be seen while taxiing
            • Cable beneath taxiway or due to signals from nearby equipment (welders, subway rails)
            • Clear screen after passing
        2) Garmin GDL 49 Weather Datalink
          a) Allows the GNS 530 MFD to display requested weather data received from satellites using the Echo Flight Message System
          b) NEXRAD (NEXt generation RADar)
            i) Description/limitations
            • Network of Doppler stations (each with range of 124 NM) covers most of United States
            • Display abnormalities
              • Ground clutter
              • Strobes and spurious radar data
              • Sun strobes
              • Metallic dust (military)
              • Shadows from buildings, mountains
            • Limitations
              • Cannot determine cloud layers or precipitation types
              • Cannot detect storms directly overhead (or high and close by)
              • Resolution is 2-12 km (intensity displayed by each data square is the highest level sampled with the 2-12 km area)
            • Echo intensity displayed by color
              Color dBZ Rain Snow
              None 0 none very light
              Green 5-25 light light-medium
              Yellow 30-50 light-intense mod-heavy
              Red 55-75 extreme
            ii) Operation
            • NEXRAD data may be requested from
            • MSG flashes when date received
            • Display/customize
              • NAV Weather Page (MENU, select View 120° or 360°)
              • Map Page (MENU, Setup Map, Weather, select NEXRAD SMBL range, ENT and/or NEXRAD DENSITY, ENT, CLR)
              • Default NAV Page
            • Shortcuts
              • Select WPT Group, Airport Location Page, or
              • Highlight any airport ID with cursor, and
              • MENU, select Request NEXRAD, Request METAR or View Text Metar, and ENT
            • Data Link Request Log Page logs requests
          c) Graphical METARs d) Textual METARs are displayed on METARS Text Page
          e) Temperature/dewpoints and Wind data may be displayed on NAV Weather Page
          f) Data Link Status Page
            i) Provides indication of integrity of Data Link
            ii) Allows monitoring of system and helps find cause of failure

      References:

Greg Gordon MD, CFII
Updated: