RADAR Flashcards
What is RADAR stabilization?
The purpose of radar stabilization is to maintain a constant radar scan at
desired tilt angle, level with the Earth’s horizon during normal aircraft operations and maneuvers.
During turns, aircraft bank will roll one wing down. As the radar scans to the wing down side it will paint excessive ground clutter. On the wing high side, the radar will scan above storms and fail to display accurate weather data to the pilot. Stabilization will adjust the tilt angle to maintain a level scan with the horizon.
During climb or decent, stabilization will adjust the tilt angle up or down as appropriate to maintain a level scan with the horizon.
If not for stabilization, the radar would scan above or below possible targets, thus missing potentially dangerous weather.
Describe how to use RADAR tilt
Generally focus tilt on FL180-250
At 10 nm, one degree of tilt motion will move the center of the beam up or down 1,000 feet. At 80 nm this one degree of motion will move the center of the beam 8,000 feet. Think about it, five degrees of tilt at 80 nm will move the center of the beam 40,000 feet.
To analyze a convective cell, the flight crew should use the tilt knob to obtain a correct display and point the weather radar beam to the most reflective part of the cell. At high altitude, a thunderstorm may contain ice particles that have low reflectivity. If the tilt setting is not adapted, the ND may display only the upper (less reflective) part of the convective cloud (overscanning). As a result, the flight crew may underestimate or not detect a thunderstorm. In order to get accurate weather detection, the weather radar antenna should also be pointed toward lower levels (i.e. below freezing level), where water can still be found. If a red area is found at a lower level, the antenna tilt should then be used to scan the area vertically. Presence of yellow or green areas at high altitudes, above a red cell, may indicate a very turbulent area.
What is the dead zone?
Often when flying in the spring, the pilot will be confronted with
two large level-three returns separated by a narrow band of level three. The temptation will be to rapidly pass through this narrow band of rough weather to the large clear area behind it. Stop, do not fly through, and fly around. This narrow band is so intense that the radar pulses are unable to make it through to the severe storm behind. This is called the dead zone.
How do you use GAIN?
When taken out of “auto” and placed in manual gain, all that can be determined from the display is a relative differ- ence between two levels. Level one, two or three displayed in manual gain will not correlate to level one, two or three
weather returns, just a relative difference between the levels. Because mountainous terrain can saturate the radar, it is often useful to use map mode and variable gain to differentiate the different return levels of the terrain. Pilots should never use
variable gain to depict weather.
Effects of Earth’s Curvature
The curvature of the Earth limits ground mapping from high alti- tude. Weather radar will not normally paint ground returns from high altitude beyond 90 nautical miles, because the Earth’s horizon at this distance and altitude will be almost parallel to the radar beam. Storms, hills, mountains, large buildings and cities will be painted.
What is GAIN?
answer
Reflectivity Limitations
The reflectivity of precipitation particles varies considerably depending on the type of precipitation particle. For example, wet hail, rain and wet snow are much more reflective than dry hail, ice crystals or dry snow. Unfortunately, aircraft radars do not see frozen precipitation as well as they see wet precipitation. So thunderstorm tops, which are composed of mostly low-reflectivity precipitation particles, aren’t seen well by aircraft radar. NEXRADs on the other hand, don’t suffer from this limitation, especially at the higher altitudes where most commercial aircraft operate.
What is shadowing/attenuation?
the size, shape and intensity of that weather as displayed to the pilot may not be accurate. The more intense the precipitation, the less distance the radar can see into and through a storm. What appears to be a thin, crescent-shaped band of precipitation (Figure 1) could just be the leading edge of a much larger area of heavy to extreme precipitation.
Radar attenuation shows up as black areas on a pilot’s weather radar display (Figure 2). Attenuation can also occur when heavy rain or ice builds up on the radome (Figure 3), when the radome is damaged, or when it isn’t well maintained.
NEXRAD detects weather at much greater distances and is not as prone to attenutation as aircraft radar. Also, if an intervening cell is intense enough, the pilot may not be able to see more distant weather behind it with the aircraft radar regardless of range selected due to attenuation.
This is an example where the ATC controller’s perspective can help keep pilots safe.
Describe the RADAR turbulence feature
The RADAR can measure turbulence when accompanied by reflective moisture. based on the Doppler effect and is sensitive to precipitation movement. Like the weather radar, the TURB function needs a minimum amount of precipitation to be effective. An area of light rainfall, depicted in green in normal mode, is shown in magenta when there is high turbulence activity. It is not used to detect CAT
Can RADAR detect the tops of thunderstorms?
No. The convective cloud and associated threats may extend significantly above the upper detection limit of the weather radar (called ‘radar top’). This means that reflectivity is not directly proportional to the level of risk that may be encountered: a convective cloud may be dangerous, even if the radar echo is weak.
What can RADAR detect?
Rainfall
Wet hail and wet turbulence
Windshear
What can’t RADAR detect?
Ice crystals, dry hail* and snow Clear air turbulence Sandstorms (solid particles are almost transparent to the radar beam) • Lightning
How does RADAR auto tilt/stabilization work?
radar uses the EGPWS terrain database and automatically adjusts the antenna tilt based on the aircraft position, altitude, and the selected ND range. Is there a gyro?
PM v PF recommended division of RADAR
To maintain a comprehensive situation awareness, the flight crew needs to monitor both the short-distance and long-distance weather. To this end, the crew should select different ranges on the Pilot Monitoring (PM) and Pilot Flying (PF) ND.
In cruise the combination of the following ranges provides good weather awareness and allows to avoid the "blind alley effect" - 160 NM on the PM ND - 80 NM on the PF ND
To avoid threatening convective weather, the flight crew should make deviation decisions while still at least 40 NM away; therefore, the following ranges should be selected on the NDs:
Pilot Monitoring (PM) adjusts ranges to plan the long-term weather avoidance strategy (in cruise, typically 160 NM and below). Pilot Flying (PF) adjusts ranges to monitor the severity of adverse weather, and decide on avoidance tactics (in cruise, typically 80 NM and below as required).
How and when should you adjust gain in manual mode instead of auto?
The sensitivity of the receiver may vary from one type of radar system to another. In the CAL (AUTO) position, the gain is in the optimum position to detect standard convective clouds. Manual settings are also available and can be used to analyze weather.
At low altitudes, reducing the gain might be justified for proper weather analysis. Due to increased humidity at lower levels, convective cells are usually more reflective and the weather radar display may have a tendency to show a lot of red areas. This can also be the case at higher altitude with significant positive ISA deviations in a very humid atmosphere (typically the Indian monsoon). In these cases, slowly reducing the gain allows the detection of threatening areas: most red areas slowly turn yellow, the yellow areas turn green and the green areas slowly disappear. The remaining red areas – i.e. the red areas that are the last to turn yellow, - are the most active parts of the cell and must be avoided (fig.17).
At high altitudes, water particles are frozen and clouds are less reflective. In this case, gain should be increased for threat evaluation purposes.
How should weather be avoided vertically?
Do not attempt to fly under a convective cloud, even when you can see through to the other side, due to possible severe turbulence, windshear, microbursts and hail. If an aircraft must fly below a convective cloud (e.g. during approach), then the flight crew should take into account all indications (visual judgement, weather radar, weather report, pilot’s report, etc) before they take the final decision.
If overflying a convective cloud cannot be avoided, apply a vertical margin of 5 000 feet
How should you avoid weather laterally?
When possible, it is advisable to try to avoid a storm by flying on the upwind side of a cumulonimbus. Usually, there is less turbulence and hail upwind of a convective cloud.
The “area of threat” identified by the flight crew (e.g. a cumulonimbus cloud) should be cleared by a minimum of 20 NM laterally whenever possible (fig.21). An additional margin may be applied in case the convective clouds are very dynamic or have a significant build-up speed.
If the aircraft trajectory goes between several convective clouds, if possible maintain a margin of at least 40 NM with the identified “area of threat”.
What cloud shapes should be avoided?
Clouds shapes, in addition to colors, should be observed carefully in order to detect adverse weather conditions. Closely spaced areas of different colors usually indicate highly turbulent zones (fig.19). Some shapes are good indicators of severe hail that also indicate strong vertical drafts (fig.20). Finally, fast changing shapes, whatever the form they take, also indicate high weather activity. finger hook u-shape scalloped edges
What is the preferred method to deviate around a thunderstorm?
it is preferable to perform lateral avoidance instead of vertical avoidance. Indeed, vertical avoidance is not always possible (particularly at high altitude) due to the reduction of buffet and performance margins. In addition, some convective clouds may have a significant build-up speed, that extends far above the radar visible top.
What does the E175 SECTOR SCAN on the weather radar do?
Reduces the sweep angle to -30deg and increases the sweep rate to 24spm
REACT
Rain Echo Attenuation Compensation Technique
