Term
3-1
What two elements define visibility? |
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Definition
A measure of the opacity of the atmosphere
The greatest horizontal distance at which selected objects can be seen and identified. |
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Term
3-2
How often should visibility be evaluated? |
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Definition
| As frequently as practicable. |
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Term
3-3
What should be done with the visibilities once they have been determined around the entire horizon circle? |
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Definition
| They should be resolved into a single value for reporting purposes. |
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Term
3-4
If the prevailing visibility varies rapidly during the time of observation, what value should be used? |
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Definition
| Use the average of all observed values. |
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Term
3-5
In what observations should prevailing visibility be reported? |
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Definition
| All observations except single element SPECIs. |
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Term
3-6
To determine the greatest distances that can be seen in all directions around the horizon circle, what visibility markers shall be used? |
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Definition
| All available visibility markers. |
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Term
3-7
Will suitable selected objects (visibility markers) be available at all reportable values? |
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Definition
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Term
3-8
How must visibility in a specified direction be estimated? |
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Definition
| The estimate is based on the appearance of available markers. |
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Term
3-9
How must the visibility estimate be made based on the object's appearance? |
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Definition
| The estimate must be based on the sharpness with which the most distant markers can be seen. |
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Term
3-10
How shall the marker appear if visibility is much greater than the distance to the markers? |
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Definition
| The marker shall be able to be seen clearly, with little loss of color, and with sharp outlines. |
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Term
3-11
Why is visibility one of the most important elements of a METAR observation? |
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Definition
| Because it affects pilots approaching or departing your station. |
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Term
3-12
From where should a visibility observation be taken? |
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Definition
| From as many locations as practicable. |
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Term
3-13
What conditions shall the visibility report describe? |
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Definition
| The actual conditions at your point of observation. |
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Term
3-14
If you are aware that conditions are different over another portion of the field, how shall this be reported? |
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Definition
| Describe the difference using the Remarks section of the report. |
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Term
3-15
What is surface visibility? |
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Definition
| The prevailing visibility determined from the usual point of observation. |
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Term
3-16
What is the definition of prevailing visibility? |
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Definition
| The visibility considered to be representative of the visibility conditions at the station. |
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Term
3-17
What visibility is considered to be representative of the visibility conditions at the station? |
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Definition
| Prevailing visibility, or the greatest visibility equaled or exceeded throughout at least half the horizon circle (180 degrees), which need not necessarily be continuous. |
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Term
3-18
What portion of the horizon circle must the greatest visibility be equaled or exceeded? |
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Definition
| At least half (180 degrees) |
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Term
3-19
Is continuity a factor when assessing the horizon circle for greatest visibility? |
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Definition
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Term
3-20
What does a sector represent? |
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Definition
| A sector represents at least one-eighth of the horizon circle (45 degrees). |
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Term
3-21
When should the horizon circle be divided into sectors of uniform visibility? |
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Definition
| When conditions are not uniform. |
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Term
3-22
If conditions are not uniform, what shall be done after the horizon circle has been divided into sectors of uniform visibility? |
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Definition
| Add the sector with the highest uniform visibility to the sector of the next highest visibility, etc., until the sectors add up to at least half the horizon circle. |
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Term
3-23
Of all the sectors of uniform visibility added to make up 180 degrees or more, which is the prevailing visibility? |
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Definition
| It is the last sector added to make up 180 degrees or more. |
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Term
3-24
What is the definition of sector visibility? |
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Definition
| It is the visibility in a specified direction that represents at least a 45 degree arc (sector) of the horizon circle. |
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Term
3-25
What is the maximum number of sectors that a horizon may be divided into? |
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Definition
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Term
3-26
What are the circumstances under which sector visibility must be reported? |
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Definition
| Whenever the visibility is not uniform in all directions and the prevailing visibility and/or sector visibility is less than three miles. |
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Term
3-27
When reporting sector visibility in the Remarks section, what shall be reported? |
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Definition
| Any sector whose visibility differs from the prevailing visibility by one or more reportable values. |
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Term
3-28
In what format/order should sector visibility be recorded in the remarks? |
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Definition
| First, enter the contraction VIS, followed by the sector (using the eight points of the compass), and the visibility in that sector. |
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Term
3-29
When coding more than one sector, in what order should sector visibility be reported if more than one sector needs to be reported? |
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Definition
| Clockwise order, starting with north. |
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Term
3-30
What is the definition of variable prevailing visibility? |
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Definition
| A condition when the prevailing visibility is less than 3 statute miles and rapidly increases and decreases by 1/2 mile or more during the period of observation. |
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Term
3-31
How shall prevailing visibility be determined when it rapidly increases and decreases during the time of observation? |
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Definition
| Use the average of all determined values, and report this in column 7a of MF1M-10C. |
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Term
3-32
When shall the limits of variability be reported in column 14, Remarks? |
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Definition
| If the average of all determined values of visibility as reported in column 7a of MF1M-10C is less than 3 miles and the variation of the minimum and maximum is 1/2 mile or more. |
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Term
| 3-33 How shall the limits of visibility be reported when the average is less than 3 miles and the variation between minimum and maximum is 1/2 mile or more? |
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Definition
| By entering the contraction VIS followed by the lowest visibility, the letter V, and the highest observable visibility. |
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Term
3-34
How shall the limits of visibility be reported on the MF1M-10C if the visibility is varying between 1/4 and 1 miles? |
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Definition
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Term
3-35
Is the reported visibility also the average of the two values given in the remarks section of variable visibility? |
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Definition
| No, even though it usually turns out that way. It is actually the average of ALL determined values of visibility. |
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Term
3-36
In what units of measure shall visibility be reported? |
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Definition
| Statute miles and fractions. |
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Term
3-37
Where shall visibility observations be taken and why? |
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Definition
| From as many locations as necessary to view as much of the horizon as practicable. |
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Term
3-38
Do natural obstructions, such as trees, hills, etc, define or obstruct the horizon? |
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Definition
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Term
3-39
Where shall charts lists, or other positive means of identifying visibility markers be posted? |
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Definition
| Near the observer's position. |
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Term
3-40
May separate lists be used for daytime and nighttime markers? |
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Definition
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Term
3-41
How shall visibility markers be classified? |
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Definition
| As daytime or nighttime markers. |
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Term
3-42
What is the definition of a daytime visibility marker? |
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Definition
| A dark or nearly dark object viewed against the horizon sky during the day. |
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Term
3-43
What is the definition of a nighttime visibility marker? |
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Definition
| Unfocused lights of moderate intensity (about 25 candela) |
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Term
3-44
List the three types of lights which may be used as nighttime visibility markers. |
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Definition
| Red obstruction lights on TV and radio towers or buildings, unfocused street lamps, and neon signs of moderate intensity. |
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Term
3-45
Why may focused lights such as airway beacons not be used as markers? |
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Definition
| Because of their intensity. |
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Term
3-46
How may focused lights be used when determining visibility? |
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Definition
| Their degree of brilliance may be used as an aid to estimating whether the visibility is greater or less than the distance to the light source. |
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Term
3-47
What shall all observers do before taking visibility observations at night? |
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Definition
| Observers shall spend as much time as practicable in the darkness to allow their eyes to become accustomed to the limited light. |
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Term
3-48
If the visibility falls halfway between two reportable values, which value shall be reported? |
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Definition
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Term
3-49
In the coded transmitted report, which group does the visibility group always follow? |
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Definition
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Term
3-50
How does the coded transmitted visibility group always end? |
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Definition
| With SM, the indicator for statute miles |
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Term
3-51
When reporting whole numbers and fractions, how are they separated? |
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Definition
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Term
3-52
What is the first step when determining the visibility? |
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Definition
| Determine the most distant object visible, using the station visibility chart as a guide. |
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Term
| 3-53 From where should visibility be determined? |
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Definition
| From an outside point where all appropriate visibility markers can be observed. |
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Term
3-54
Once the most distant object visible has been determined, how shall the visibility in the direction of this object be estimated? Give two conditions. |
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Definition
1. If the object is barely identifiable, consider the visibility to be the same distance to this object.
2. If the outlines of the object are in sharp relief, estimate the distance that can be seen beyond this object. |
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Term
3-55
After the visibility of the most distance object has been determined, what shall the observer look for next? |
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Definition
| The visibility in other directions to determine if the above value is representative of all directions. |
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Term
| 3-56 What shall the observer do if the visibility is different in other sectors but is relatively uniform in each sector? |
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Definition
| Estimate the value of visibility in each sector. |
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Term
3-57
On MF1M-10C, enter the prevailing visibility in column 7a as follows:
1. If the visibility is the same in all directions___________.
2. If the visibility differs in various sectors ___________.
3. If the visibility is variable ____________. |
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Definition
1. enter this value
2. select a single value that is the greatest visibility equaled or exceeded throughout at least half the horizon circle.
3. enter the average of all values. |
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Term
3-58
When should a remark be made in column 14 in accordance with sector visibility. |
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Definition
| If the visibility is non-uniform with the prevailing visibility and/or sector visibility is less than 3 miles. |
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Term
3-59
When should a remark be made in column 14 in accordance with variable prevailing visibility? |
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Definition
| If the visibility is variable with the average visibility less than 3 miles and the variation between the minimum and maximum 1/2 mile or more. |
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Term
3-60
What reportable visibility values are reported in increments of 1/16? 1/8? 1/4? 1? 5? |
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Definition
| 0-3/8; 3/8-2; 2-3; 3-15; 15+ |
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