DGCA Air Navigation: Airborne Weather Radar Questions
188 exam-style Airborne Weather Radar questions for the DGCA Air Navigationpaper (CPL & ATPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.
- Q1
A weather radar, set to the 100 NM scale, shows a squall at 50NM. By changing the scale to 50 NM, the return on the radar screen should:
- A increase in area and move to the top of the screen
- B increase in area and appear nearer to the bottom of the screen
- Cdecrease in area but not change in position on the screen
- Ddecrease in area and move to the top of the screen
Show answer
Correct answer: A. increase in area and move to the top of the screen
Rescaling from 100 NM to 50 NM doubles the size of the picture, so the squall at 50 NM enlarges and moves out to the top edge of the display.
- Q2
Airborne weather radar systems use a wavelength of approximately 3 cm in order to:
- Adetect the larger water droplets
- Btransmit at a higher pulse repetition frequency for extended range
- C obtain optimum use of the Cosecant squared beam
- D detect the smaller cloud formations as well as large
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Correct answer: A. detect the larger water droplets
A wavelength of about 3 cm is used because it is efficiently reflected by the larger water droplets in significant weather, allowing precipitation to be detected.
- Q3
In weather radar the use of a cosecant beam in 'Mapping' mode enables:
- Ascanning of a large ground zone producing echos whose signals are practically independent of distance
- B better reception of echos on contrasting terrain such as ground to sea
- C a greater radar range to be achieved
- Dhigher definition echoes to be produced giving a clearer picture
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Correct answer: A. scanning of a large ground zone producing echos whose signals are practically independent of distance
The cosecant-squared beam in mapping mode illuminates a wide ground strip so that the strength of the returns is practically independent of range, giving an even picture.
- Q4
The ISO-ECHO facility of an airborne weather radar is provided in order to:
- A detect areas of possible severe turbulence in cloud
- Bgive an indication of cloud tops
- Cinhibit unwanted ground returns
- D extend the mapping range
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Correct answer: A. detect areas of possible severe turbulence in cloud
The iso-echo facility blanks the centre of the strongest returns to reveal steep rainfall gradients, which mark areas of probable severe turbulence.
- Q5
In Airborne Weather Radar (AWR), the main factors which determine whether a cloud will be detected are:
- Asize of the water drops,wavelength/frequency used
- Brange from cloud,wavelength/frequency used
- Csize of the water drops,diameter of radar scanner
- Drotational speed of radar scanner,range from cloud
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Correct answer: A. size of the water drops,wavelength/frequency used
Whether a cloud is detected depends chiefly on the size of its water drops and on the wavelength or frequency of the radar, since reflectivity depends on drop size relative to wavelength.
- Q6
In the MAPPING MODE the airborne weather radar utilises a:
- A fan shaped beam effective up to a maximum of 50 NM to 60 NM range
- Bfan shaped beam effective up to a range of 150 NM
- C pencil beam to a maximum range of 60 NM
- Dpencil beam effective from zero to 150 NM
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Correct answer: A. fan shaped beam effective up to a maximum of 50 NM to 60 NM range
In mapping mode the weather radar uses a wide fan-shaped cosecant beam, which is effective only out to about 50 to 60 NM.
- Q7
In order to ascertain whether a cloud return on an Aircraft Weather Radar (AWR) is at or above the height of the aircaft, the tilt control should be set to: (Assume a beam width of 5°)
- A2.5° up
- B0°
- C 2.5° down
- D5° up
Show answer
Correct answer: A. 2.5° up
With a 5 degree beam width, tilting the aerial 2.5 degrees up places the lower edge of the beam on the horizontal, so any cloud still painted lies at or above the aircraft's level.
- Q8
Which of the following cloud types is most readily detected by airborne weather radar when using the 'weather beam'?
- A cumulus
- Bcirrocumulus
- C stratus
- Daltostratus
Show answer
Correct answer: A. cumulus
Cumulus and cumulonimbus contain large water droplets that reflect strongly, so of the listed clouds the cumulus is the most readily returned by the weather beam, whereas thin high or layer clouds give weak echoes.
- Q9
When switching on the weather radar, after start-up, a single very bright line appears on the screen.This means that the:
- Ascanning of the cathode ray tube is faulty
- Btransmitter is faulty
- C scanner is not rotating
- D receiver is faulty
Show answer
Correct answer: C. scanner is not rotating
If the antenna stops sweeping while the timebase keeps painting outward along one fixed azimuth, the trace repeatedly retraces the same radial and appears as a single very bright stationary line, indicating the scanner is not rotating.
- Q10
In which mode of operation does the aircraft weather radar use a cosecant radiation pattern.
- A MAPPING
- B CONTOUR
- CWEATHER
- D MANUAL
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Correct answer: A. MAPPING
In the mapping (ground-mapping) mode the antenna uses a cosecant-squared radiation pattern so that terrain at differing slant ranges is illuminated with roughly even energy for a uniform ground picture.
- Q11
In an Airborne Weather Radar that has a colour cathode ray tube (CRT) the areas of greatest turbulence are indicated on the screen by:
- A colour zones being closest together
- B blank iso-echo areas where there is no colour
- C large areas of flashing red colour
- D iso-echo areas which are coloured black
Show answer
Correct answer: A. colour zones being closest together
Areas of greatest turbulence show where the rainfall gradient is steepest, so on a colour display they appear where the colour bands are packed closest together.
- Q12
Which of the following lists phenomena that CANNOT be detected by weather radar?
- A snow, clear air turbulence
- B dry hail, clear air turbulence
- C clear air turbulence, turbulence in cloud with precipitation
- D snow, turbulence in clouds with precipitation
Show answer
Correct answer: B. dry hail, clear air turbulence
Weather radar detects energy reflected from water droplets, so clear air turbulence, which has no precipitation, cannot be seen, and dry (ice) hail is also a very poor reflector, so both are effectively undetectable.
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