09 Weather Radar

Question 1

At what frequency does Weather Radar operate?

Answer 1

9 GHz

Question 2

Describe the two Radiation Patterns which are used by Weather Radar?

Answer 2

• Pencil (or Cone) shaped pattern: used for weather detection
• Cosecant Squared (or Spoiled) pattern: used for ground mapping

Question 3

What is the approximate range of the Ground Mapping function of a Weather Radar?

Answer 3

60 - 80nm

Question 4

Regarding a Weather Radar, what does the Gain Control do?

Answer 4

• Gain control changes the sensitivity of the Weather Radar output
• e.g. A high gain means that small amounts of water droplets are displayed as a more serious colour on the display

Question 5

Regarding a Weather Radar, what is the danger of having a Gain Control set too high?

Answer 5

Minor weather maybe miss-interpreted as more severe and could lead to unnecessary avoidance

Question 6

Regarding a Weather Radar, what is the danger of having a Gain Control set too low?

Answer 6

Severe weather may not be displayed as being server and could lead to an AC flying into dangerous weather

Question 7

Regarding a Weather Radar, what are the two settings for the Tilt Control?

Answer 7

• Stabilised Radar: Weather Radar is tilted in relation to the local horizon
• Un-stabilised Radar: Weather Radar is tilted in relation to the longitudinal axis of the AC

Question 8

Regarding a Weather Radar, what is the formula for calculating the height of the Cloud Tops?

Answer 8

• Cloud Top (ft) = (Range to Tgt (nm) x Tan (Tilt Angle - (Beam Width / 2))) x 6080
• This gives the height of the cloud in relation to the AC
• I.e. If this is above the AC then will need to add the AC height in order to get height above ground/MSL

Question 9

Regarding a Weather Radar, arrange the following types of water droplet in order of descending returns;

• Dry Hail
• Wet Hail
• Dry Snow
• Wet Snow
• Drizzle
• Large/Med Water Droplet

Answer 9

• Wet Hail
• Large/Med Water Droplet
• Wet Snow
• Drizzle
• Dry Hail
• Dry Snow

Question 10

Regarding a Weather Radar, what is the standard tilt angle during the Take Off and Climb?

Answer 10

Initially set to + 4 degrees tilt angle, slowly reducing during the climb

Question 11

Regarding a Weather Radar, what is the standard tilt angle during the Cruise?

Answer 11

Set to - 2 degrees tilt in order to detect long range weather ahead

Question 12

Regarding a Weather Radar, what is the standard tilt angle during the Final Approach and Landing?

Answer 12

• Initially set to a negative tilt
• As the AC gets closer to the ground, progressively increase the tilt angle to remove ground ‘clutter’
• May end up as high as + 4 degrees tilt

Question 13

How does the Wind Sheer detection work on a Weather Radar?

Answer 13

Uses Doppler Shift to measure the movement of water droplets in the air

Question 14

Modern AC Weather Radars are stabilised by which means?

Answer 14

Inputs from the AC attitude system

Question 15

In what axes is the Weather Radar stabilised?

Answer 15

• Roll and Pitch

- As the AWR sweeps left to right through the yaw axis, it would be impractical to stabilise it in yaw

Question 16

What is the principle of operation for the ISO-Echo function on a weather radar?

Answer 16

• Used to identify possible areas of severe turbulence
• Either displayed as a black area within the white cloud on monochromatic displays
• Or via the colour gradient on colour displays
• A thin gap between the edge of the white and the black area or a steep colour gradient, depict areas of worst turbulence