NATIONAL BUREAU OF STANDARDS REPORT

9958

A SUMMARY OF LOW VISIBILITY CONDITIONS AT THE ARCATA AIRPORT

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

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I
NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT

2120414 November 1968

HBS REPORT

9958

A SUMMARY OF LOW VISIBILITY CONDITIONS AT THE ARCATA AIRPORT

By

James E. Davis

J. W. Simeroth

J. C. Wilkerson

IMPORTANT NOTICE NATIONAL BUREAU OF ST

for use within the Government, and review. For this reason, th whole or in part, is not autho Bureau of Standards, Washingt

the Report has been specifically

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

ss accounting documents intended

subjected to additional evaluation

listing of this Report, either in e Office of the Director, National

by the Government agency for which

:opies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
cctI
A SUMMARY OF LOW VISIBILITY CONDITIONS AT THE ARCATA AIRPORT

By

James E. Davis

J. W. Sirneroth

J. C. Wilkerson

This report summarizes data on occurrence of low visibility conditions at the Areata (California) Airport for a period from 1957 through 1967. The times

with transmittances below 0. 5 over a 500-foot baseline (equivalent to a transmissivity of about 10~5 per statute mile) are given for a 10-year period. The

times with runway visual ranges below 1000 feet, 800 feet, and 600 feet for

1965, 1966 and 1967 are also included. The accumulated times as reported

by the Federal Aviation Administration Flight Service Station observers are summarized over the period 1962 through 1967 for several ranges of low visibility

and low ceiling.

1. INTRODUCTION

Several requests for information on the frequency and characteristics of fog

at the Areata Airport are received each year. Although the specific data desired

depend on the particular application intended, a general summary of the hours

of fog and the frequency distribution of occurrence will help supply the need for

information.

Much of the data on low visibility conditions has been reported in piecemeal

form in Quarterly Progress Reports, specific task reports, etc. W

T hen presented

in this manner the information does not give a full picture. The reports of the

Landing Aids Experiment Station (LAES) located at Areata Airport included

summaries of fog occurrence during the time of its operation (1946 through 1949).

Summaries of low visibility conditions as determined from transmissometer

records and Federal Aviation Administration (FAA) observations are given in

this report for 1957 through 1967.

2. TEN-YEAR SUMMARY OF LOW VISIBILITY CONDITIONS

Instrument records are perhaps the most useful source of information on

fog because of continuity and precise knowledge of what is being measured.

Fortunately, several years of Areata transmissometer records are available.

There has been a transmissometer located near the touchdown area or runway 31

for most of the time since 1946 and continuous records for more than 10 years are
%

I

i
- 2 -

available. There was one change in location of the transmissometer in 1962

when the Weather Bureau (WB) installed the transmissometer for official use

behind the ILS glidepath building and the NBS transmissometer on the runway side

of the glidepath building was removed. The earlier transmissometer had a 750-

foot baseline and the WB instrument has a 500-foot baseline.

In this summary, the times when the transmittance was less than 0. 5 for the

500-foot baseline unit (0. 35 for the 750-foot baseline unit) were considered low

visibility periods. (A transmittance of 0. 5 over a 500-foot baseline corresponds

to a transmissivity of approximately 10~5 per statute mile. ) These transmittances

are equivalent to meteorological visibilities of 2100 feet by day and 4300 feet by

night. Transmittance is used in this summary instead of visibility as the transmittance in a given atmospheric condition is the same for day and night.

The times that the transmittance over a 500-foot baseline was below 0. 5 as measured by the transmissometer near the touchdown area of runway 31 is

summarized in table 1 for the 10-year period from 1957 through 1966. The data are totaled by the month and the year fcr day and night. Some of the data are also

presented in figures 1 to 4 for easier assimilation.

3. LOW RUNWAY VISUAL RANGE CONDITIONS

The efforts to improve air operations by making it practical to land aircraft

in low visibility conditions are now centered on the requirements for the low end

of Category II and for Category III operations. Most airports have some

knowledge of the time that conditions are below operating minimums or are below

Category I limits but data concerning the frequency and duration of periods of very

dense fog are meager. To obtain some idea of the frequency and duration of

conditions that might be encountered, the records of the WB transmissometer at Areata for 1965, 1966 and 1967 were reviewed and the date, time, and duration

of all periods when RVR would have been less than 1000, 800, and 600 feet were

tabulated. The data are separated into day and night conditions. The RVR’

s

were based on the runway lights being operated at 100 percent intensity. The

transmittances for RVR at 1000, 800, and 600 feet are, respectively, for a 500-

foot baseline in daytime 0. 029, O.QIL and 0. 0009 and at night 0. 0012, 0. 00012,

and 0. 0000018; and for a 250-foot baseline in daytime 0. 197, 0. 103, and 0. 030

and at night 0. 035, 0. Oil, and 0. 0013. The transmittances used in this report are more accurate than those which could be obtained from most operational

transmissometers in these low visibility conditions because an automatic range

control was used to increase indicator sensitivity by a factor of five for low

transmittances and the individual pulses from the receiver were counted in the

very low visibility conditions. Part of this time the records from a 250-foot

baseline transmissometer located in the same area were used to obtain more

accurate measurements.
I

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Table

I.

Summary

of

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conditions

at

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Areata

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the

period

1957-196

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corresponding

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night.
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Figure

I.

Monthly

hours

of

low-visibility

conditions

at

the

Areata

Airport

by

the

year

for

1957-

1966.
%
- 5 -

Figure

2.

Low-visibility

conditions

ui

the

Areata

Airport

by

month

for

1957-1966.
% /
1000

- 6 -

i.

o o o o o

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Figure

3.

Yearly

hours

of

nighttime

low-visibility

uonditions

at

the

Areata

Airport

by

month

for

1957-1966.
%
1000

- 7 -

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oo

oo

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Jan.

Feb.

Mar.

Apr.

May

June

July

Aug.

Sep.

Oct.

Nov.

Dec.

Figure

4.

Yearly

hours

of

daytime

low

visibility

conditions

at

the

Areata

Airport

by

month

for

1957-1966.
«;

i

*
- 8 -

Since a large portion of the low RVR occurrences last only a few minutes

and low RVR’s may re-occur after a short period of clearer conditions the data

were also evaluated by considering periods in which clearing above the RVR level

lasted less than 30 minutes into a single period of low RVR. The duration of

these combined periods was considered as from the beginning of the initial

occurrence to the end of the final occurrence. The total time, number of periods,

and maximum and average duration of periods are given in tables 3, 4, and 5 for the

individual and combined occurrences.

NOTE: The RVR computers are designed to provide an RVR readout of 1000 feet for any RVR between 900

feet and 1100 feet. Similarly, a reported RVR of

800 feet includes any RVR between 700 feet and 900

feet, etc. Therefore, in table 3 the periods

listed are for RVR’s below 900 feet actual; in

table 4, the RVR’s are below 700 feet actual; and

in table 5, the RVR’s are below 500 feet actual.

In table 6 the RVR’s values listed are actual ranges

computed from the transmittances.

These data are summarized in table 2. Details of the occurrences of fogs

with an RVR of less than 1000 feet are given in table 3 and figures 5, 6, and 7; with an RVR of less than 800 feet in table 4 and figures 8, 9, and 10; with an RVR of less than 600 feet in table 5. The time of day and duration of these

conditions are included in this report because they may be of interest in

evaluating scheduling and length of possible delays. At Areata where fog

conditions frequently occur, the transmittance over a 500-foot baseline is below

0. 5 about six percent of the time, the R VR is below 1000 feet about one percent

of the time, below 800 feet about 0. 2 percent of the time, and below 600 feet

only a few hours each year.

Note from tables 2 and 5 that RVR’s less than 600 feet occurred only once at night (for 0. 02 hours) and 2 5 times by day (for a total of 4. 30 hours) during the

three years covered by the this report. More detailed knowledge of the RVR

during these periods is given in table 6. In preparing this table the minimum RVR

during each period was determined from the transmissometer record charts

whenever this was possible. However, the sensitivities of the transmissometers

installed at Areata were not sufficient to provide transmittance measurements in the

densest of these fogs. (During parts of 1965 and 1966 only 500-foot baseline

instruments were available. During the remainder of 1965 and 1966 and throughout

1967, 250-foot baseline instruments were available. )
(
- 9 -

Table 2 Summary, Periods of Low RVR at Areata Airport

during 1965, 1966, and 1967

a. “Reported” RVR below 10Q0 feet

Individual Occurrences

Total time (hours)

Number of occurrences Maximum duration (hours)

Mean duration (hours)

Median duration (hours)

Combined Periods

Total time (hours)

Number of occurrences Maximum duration (hours)

Mean duration (hours)

Median duration (hours)

NIGHT (Hours)

1965 1966 1967 Period

31. 19 4. 49 19. 71 55. 32 96 22 83 201

2. 92 0. 62 1. 62 2. 92

0. 32 0. 22 0. 24 0. 28

0. 15 0. 16 0. 13 0. 15

38. 61 5. 83 24. 59 69. 03

50 16 39 105

5. 07 0. 90 2. 45 5. 07

0. 77 0. 39 0. 61 0. 66

0. 38 0. 37 0. 27 0. 33

DAY (Hours)

1965 1966 1967 Period

52. 15 35. 87 29. 84 117. 71 186 125 119 430

3. 10 1. 70 2. 58 3. 19

0. 29 0. 29 0. 25 0. 27

0. 08 0. 10 0. 08 0. 08

65. 80 47. 59 35. 86 149. 25

48 41 52 144

8. 32 5. 58 3. 00 8. 32

1. 26 1. 16 0. 70 1. 04

0. 76 0. 70 0. 57 0. 68

b. “Reported” RVR below 800 feet

NIGHT (Hours) DAY (Hours)

1965 1966 1967 Period 1965 1966 1967 Period

Individual Occurrences

Total time (hours) 0. 17 0 3. 26 3. 43 13. 88 12. 02 10. 67 36. 57 Number of occurrences 1 0 .'25 29 54 48 64 166 Maximum duration (hours) - 0. 52 0. 52 1. 92 1. 68 1. 10 1. 92 Mean duration (hours) - 0. 12 0. 12 0. 26 0. 24 . 17 0. 22 Median duration (hours) - 0. 08 0. 08 0. 12 0. 08 0. 07 0. 08

Combined Periods

Total time (hours) 0. 17 0 4. 61 4. 78 17. 54 14. 62 15. 80 47. 96 Number of occurrences 1 0 16 17 27 23 25 74 Maximum duration (hours) - 0. 88 0. 88 2. 37 1. 8 5 2. 47 2. 47 Mean duration (hours) - 0. 29 0. 28 0. 67 0. 70 0. 63 0. 65 Median duration (hours) - 0. 21 0. 17 0. 31 0. 47 0. 38 0. 52

c. “Reported” RVR below 600 feet

NIGHT (Hours) DAY (Hours)

1965 1966 1967 Total 1965 1966 1967 Total

Total time (hours) - 0. 02 0. 02 0. 77 3. 24 1. 25 5. 26 Number of occurrences - 1 1 11 10 3 24 Maximum duration (hours) - - - 0. 30 1. 33 0. 77 1. 33 Mean duration (hours) - - 0. 07 0. 32 0. 42 0. 22 Median duration (hours) - - 0. 03 0. 13 0. 43 0. 07

Combined Periods

Total time (hours) - 0. 02 0. 02 1. 15 3. 76 1. 25 6. 16 Number of occurrences - 1 1 8 6 3 17 Maximum duration - - 0. 02 0. 63 1. 33 0. 77 1. 33 Mean duration (hours) - 0. 02 0. 14 0. 63 0. 42 0. 36 Median duration (hours) - 0. 02 0. 04 0. 62** 0. 43 0. 10 Combined periods containing conditions above the RVR level lasting less than

30 minutes are considered as a single occurrence with the duration of the period

extending from the beginning of the first period to the end of the last period.

**Three periods had a duration of 0. 17 or less and three periods had durations of

1. 07 or more.
*

<
- 10 -

Table 3

’ft 3. a. Periods ol RVR below a Reported RVR of 1000 feet at Areata Airport during 1965.

(Based on runway lights operated at brightness step 5).

DATE’ LOCAL TIME NIGHT DAY DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours Hours 1965 Start Stop Hours Hoars

Jan. 13 2323 2325 . 03 Jan. 16 0230 0239 . 15

2116 2137 . 35

Jan. 14 0057 0113 . 27 2303 2314 . 18

1101 1102 . 02

1115 1132 . 17 Jan. 17 0124 0159 . 58

1136 1146 . 17

1153 1155 . 03 Jan. 18 1917 192 5 . 13

1157 1158 . 02

1200 1204 . 07 Jan. 29 0235 0307 . 53

1210 1217 . 12 0717 0737 . 33

1729 1750 . 35

1758 1808 . 17 Jan. 30 0736 0740 . 07

1856 1859 . 05 0744 0846 1. 03

1901 2032 1. 52 08 54 08 57 . 05

2039 2218 1. 65 0909 0940 . 52

2222 2224 . 03 1037 1147 1. 17

2233 2243 . 17 1152 1157 . 08

2248 2254 . 10 1226 1326 1. 00

2304 2333 . 48 1352 1411 . 32

Jan. 15 0005 0023 . 30 Feb. 1 0654 0844 1. 83

0100 0101 . 02 0850 0906 • 27

0742 0752 . 17

0759 0819 . 33 Feb. 2 0352 0410 . 30

0825 0829 . 07 1014 1017 . 05'

0851 0955 1. 07 1021 1048 . 45

1005 1010 . 08 1150 1154 . 07

1017 1030 . 22

1041 1047 . 10 Feb. 17 1637 1643 . 10

1048 1127 . 65 1647 1651 . 07

1129 1304 T“H LO 00 1652 1653 . 02

1305 1407 1-* o 00 1658 1735 . 62

1409 1411 . 03 2004 2042 . 63

1415 1416 . 02

1417 1430 . 22

1444 1451 . 12

1457 1500 . 05

1506 1516 . 17

1517 1522 . 08

1 535 1539 . 07

1543 1544 . 02

1546 1549 . 05

1553 1555 . 03

1556 1557 . 02

1558 1601 . 05

1653 1700 . 12

- 11 -

Table 3, cont’d.

3. a cont’d.

DATE LOCAL TIME NIGHT .DAY

1965 Start Stop Hours Hours

Feb. 18 0352 0647 2. 92

0647 0654 . 12

0738 0740 . 03

0853 0955 1. 03

0956 0957 . 02

1003 1005 . 03

1006 1008 . 03

1012 1013 . 02

1015 1017 . 03

1020 1040 . 33

1049 1111 . 37

1124 1125 . 02

1129 1131 . 03

1141 1146 . 08

1151 1157 . 10

1201 1203 . 03

1231 1234 . 05

1247 1257 . 17

1600 1735 1. 58

1740 1805 . 42

1812 1815 . 05

1843 1848 . 08

1853 1856 . 05

1857 1858 . 02

1905 1909 . 07

1914 1915 . 02

1928 1937 . 15

Feb. 19 0304 0305 . 02

1728 1735 . 12

Feb. 20 0654 0717 . 38

0731 0811 . 67

0837 9954 1. 28

1415 1416 . 02

1424 1427 . 05

1652 1722 . 50

1727 1735 . 13

1900 1901 . 02

1952 1954 . 03

2035 2036 . 02

2043 2050 . 12

DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours Hours

Feb. 21 0224 0227 . 05

0242 0323 . 68

0349 0356 . 12

0416 0420 . 07

Apr. 26 0526 0601 . 58

0605 0614 . 15

June 10 0305 0339 . 57

July 14 0512 0515 . 05

0528 0532 . 07

0534 0553 . 32

0647 0649 . 03

0700 0702 . 03

July 17 0707 0717 . 17

0726 1728 . 03

0744 0757 . 22

0759 0800 . 02

0802 0803 . 02

July 23 0514 0519 . 08

July 28 0525 0531 . 10

0536 0600 . 40

0607 0609 . 03

0611 0615 '. 07

0616 0634 . 30

0637 0641 . 07

0645 0650 . 08

0652 0703 . 18

0704 0706 . 03

- 12 - Table 3, cont’d.

3. a cont’d

DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours Hours

Aug 7 1909 1911 . 03

1924 193 2 . 13

2006 2009 . 05

2309 2318 . 15

2325 2335 . 17

Aug. 8 0046 0059 . 22

0146 0147 . 02

181« 1819 . 02

1836 1838 . 03

1846 1851 . 08

18 54 1857 . 05

1900 1906 . 10

1909 1926 . 28

Aug. 9 0737 0747 . 17

0748 0754 . 10

0755 0800 . 08

0801 0803 . 03

1820 1841 . 35

1843 1849 . 10

1901 1904 . 05

1909 1913 . 07

Aug. 10 0655 0657 . 03

0700 0718 . 30

2303 2306 . 05

2327 2341 . 23

2352 2400 . 13

Aug. 11 0000 0009 . 15

0102 0105 . 05

0528 0617 . 82

0648 0650 . 03

Aug. 13 0102 0122 . 33

0211 0217 . 10

0248 0249 . 02

0524 0526 . 03

0530 0635 1. 08

0820 0824 . 07

0830 0831 . 02

0901 0904 . 05

DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours Hours

Sept. 14 0631 0647 . 27

0648 0650 . 03

0

7 21 0723 . 03

0729 0747 . 30

Sept. 21 0214 0219 . 08

0410 0414 . 07

0447 0453 . 10

0456 0526 . 50

0606 0814 2. 13

0822 0827 . 08

Sept. 22 1745 1746 . 02

1749 1755 . 10

1802 1805 . 05

1807 1809 . 03

Sept. 23 0612 0918 3. 10

Sept. 29 0807 0814 . 12

Oct. 5 2152 2307 1. 25

Oct. 6 0455 0515 . 33

0754 0805 . 18

Oct. 7 0738 0851 1 22

08 53 0856 . 05

0858 0903 . 08

0905 0911 . 10

0913 0921 . 13

0922 0925 . 05

0926 0930 . 07

1809 1855 . 77

2223 2241 . 30

2250 2400 1. 17

Oct. 8 0000 0011 . 18

0724 0727 . 05

0732 0735 . 05

0736 1015 2. 65

1813 1815 . 03

1820 1826 . 10

1829 1834 . 08
It
- 13

Table 3,

3. a cont’d

DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours Hours

Oct. 13 0025 0029 . 07

0056 0102 . 10

0130 0152 . 37

Oct. 19 1056 1219 1. 27

1618 1620 . 03

1625 1629 . 07

1631 1540 . 15

Oct. 26 2139 2141 . 03

2143 2144 . 02

Oct. 28 0659 0700 . 02

0755 0937 1. 70

0945 0955 . 17

1113 1115 . 03

1130 1131 . 02

1145 1158 . 22

Oct. 29 0531) 0605 . 58

0800 1047 2. 78

1048 1050 . 03

1051 1053 . 03

1055 1108 . 22

1109 1112 . 05

1118 1129 . 18

1140 1236 . 93

1238 1241 . 05

1449 1452 . 05

1455 1456 . 02

1458 1500 . 03

1501 1618 1. 28

1620 1624 . 07

1625 1627 . 03

1628 1629 . 02

1631 1622 . 03

1634 1626 . 03

1640 1641 . 02

1648 1650 . 03

1716 1719 . 05

1720 1726 . 10

1727 1731 . 07

1732 1817 . 75

1923 1948 . 42

2046 2209 1. 38

2247 2259 . 20

2312 2320 . 13

2331 2333 . 03

2343 2400 . 37

cont’d.
<
- 14 -

Table 3, cont’d.

£ 3. a cont’d.

DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours Hours

Oct. 30 0000 0017 . 28

0048 0118 . 50

0317 0326 . 15

0339 0406 . 45

0452 0453 . 02

0455 0456 . 02

0500 0504 . 07

0522 0542 . 33

0653 0743 . 83

0901 1012 1. 18

1021 1050 . 48

1307 1308 . 02

1707 1709 . 03

1716 1717 . 02

1722 1805 . 72

1813 1817 . 07

1837 1843 . 10

1848 1858 . 17

4*

1913 1918 . 08

1942 1944 . 03

1948 2003 . 25

2006 2028 . 37

2035 2041 . 10

2053 2149 ... 93

2153 2312 1. 32

2326 2341 . 25

Total time for 1965 (hours) 31. 19 52. 15

Number of occurrences 96 186

Maximum duration (hours) 2. 92 3. 10

Mean duration (hours) 0. 32 0. 29

Median duration (hours) 0. 15 0. 08

^Combined periods

Total time for 1965 (hours) 38. 61 65. 80

Number of occurrences 50 48

Maximum duration (hours) 5. 07 8. 32

Mean duration (hours) 0. 77 1. 26

Median duration (hours) 0. 38 0. 76

^Combined periods containing conditions above the RVR level lasting less than 30 minutes

are considered as a single occurrence with the duration of the period extending from the

vfD’gmmng 0f the first period to the end of the last period.
<

T>

c
- 15 -

Table 3, cont’d.

3. b. Periods of RVR below a Reported RVR of 1000 feet at Areata Airport during 1966.

(Based on runway lights operated at brightness step 5). DATE LOCAL TIME NIGHT DAY DATE LOCAL TIME NIGHT DAY

1966 Start Stop Hours Hours 1966 Start Stop Hours Hours

Jan. 6 2056 2107 . 13 May 3 0545 0554 . 15

2114 2123 . 15 0559 0614 . 25

2138 2153 . 25 0615 0634 . 32

0640 0643 . 05

Jan. 7 0039 0054 . 25 0653 0658 . 08

0125 0132 . 12 0702 0712 . 17

Feb. 17 0145 0147 . 03 May 2 5 0557 0727 1. 50

Mar. 6 0659 0703 . 07 May 26 1821 1824 . 05

0706 0721 . 25 1847 1851 . 07

Apr. 1 0106 0108 . 03 July 24 0610 0617 . 12

0621 0624 . 05

Apr. 15 0520 0530 . 17 0626 0640 . 23

0538 0548 . 17 0647 0658 . 18

0550 0552 . 03 0708 0709 . 02

0603 0606 . 05 0754 0802 . 13

0613 0616 . 05 0809 0823 . 23

0632 0644 . 20

0650 0703 . 22 Aug. 5 0609 0712 1. 05

0707 0749 . 70

0808 0811 . 05 Aug. 6 0617 0637 . 33

0818 0822 . 07 0647 0653 . 10

0828 0847 . 32 0656 0817 1. 35

0900 0901 . 02

0904 0907 . 05 Aug. 14 0600 0615 . 25

0934 0939 . 08 0622 0638 . 27

1203 1207 . 07

1228 1230 . 03 Aug. 16 0610 0612 . 03

1240 1242 . 03 0613 0614 . 02

0624 0712 . 80

Apr. 16 0638 0640 . 03

0645 0706 . 35 Aug. 21 0600 0613 . 22

0627 0632 . 08

Apr. 23 0523 0608 . 75 0640 0642 . 03

0609 0629 . 33 0928 0930 . 03

0635 0638 . 05 0932 0935 . 05

0937 0940 . 05
4(
- 16 -

Table 3, cont’d.

3. b. cont’d.

DATE LOCAL TIME NIGHT DAY

196(5 Start Stop Hours Hours

Sept. 3 0816 0824 . 13

0827 0829 . 03

0903 0906 . 05

0912 0918 . 10

Sept. 4 0520 0643 1. 38

0715 0723 . 13

0847 0848 . 02

0853 08 54 . 02

Sept. 5 0450 0500 . 17

0544 0609 . 42

0640 0822 1. 70

Sept. 6 1650 1653 . 05

1657 1659 . 03

1710 1714 . 07

1716 1717 . 02

1753 1758 . 08

Sept. 7 0218 0242 . 40

Sept. 18 0502 0532 . 50

Sept. 21 0610 0624 . 23

Sept. 26 0552 0558 . 10

0634 0643 . 15

0645 0654 . 15

0655 0720 . 42

Sept. 30 0746 0747 . 02

0834 0836 . 03

08 52 08 58 . 10

Oct. 6 1002 1004 . 03

Oct. 23 1052 1230 1. 63

1238 1241 . 05

1242 1254 . 20

1303 1304 . 02

1307 1314 . 12

1816 1839 . 38

DATE LOCAL TIME NIGHT DAY

1966 Start Stop Hours Hours

Oct. 24 0740 0742 . 03

0805 0904 . 98

0950 1122 1. 53

1124 1131 . 12

1133 1144 . 18

1147 1150 . 05

1641 1644 . 05

1655 1657 . 03

1659 1700 . 02

1702 1704 . 03

1707 1708 02

1713 1725 20

1727 1810 . 72

2350 2400 . 17

Oct. 25 0000 0004 . 07

0735 0908 1. 55

0920 0923 . 0 5 092 5 0938 . 22

1000 1048 . 80

1105 1134 . 48

1136 1232 . 93

1234 1236 . 03

1238 1243 . 08

1245 1300 . 25

1304 1306 . 03

1307 1310 . 05

Oct. 27 0923 0926 . 0 5

Oct. 28 2035 2040 . 08

2043 2120 . 62

2242 22 52 . 17

Oct. 30 0206 0221 . 25

Nov. 2 0520 0525 . 08

0547 0556 . 15

0637 0645 . 13

0645 0823 1. 63

08 52 0947 . 92

0950 0951 . 02

1015 10 52 . 62

1054 1116 . 37

1120 1129 . 15

- 17 -

Table 3, cont’d

3. b. cont’d.

DATE LOCAL TIME NIGHT DAY

1966 Start Stop Hours Hours

Nov. 4 0700 0705 . 08

0712 0715 . 05

0719 0809 . 83

0914 1040 1. 43

1044 1111 . 45

1115 1119 . 07

1125 1127 . 03

1133 1134 . 02

Dec. 16 0736 0741 . 08

0810 0820 . 17

0842 0937 . 92

Dec. 17 0837 0839 . 03

Total time for 1966 (hours) 4. 49 35. 87

Number of occurrences 22 125

Maximum duration (hours) 0. 62 1. 70

Mean duration (hours) 0. 22 0. 29

Median duration (hours) 0. 16 0. 10

^Combined Periods

Total time for 1966 (hours) 5. 83 47. 59

Number of occurrences 16 41

Maximum duration (hours) 0. 90 5. 58

Mean duration (hours) 0. 39 1. 16

Median duration (hours) 0. 37 0. 70

*Combined periods containing conditions above the RVR level lasting less than 30 minutes

are considered as a single occurrence with the duration of the period extending from the

beginning of the first period to the end of the last period.
f

(l
- 18 -

Tabic 3, cont’d.

3. c. Periods of RVR below a Reported RVR of 1000 feet at Areata Airport during 1967.

(Rased on runway lights operated at brightness step 5). DATE LOCAL TIME NIGHT DAY DATE LOCAL TIME NIGHT DAY

1967 Start Stop Hours Hours 1967 Start Stop Hours Hours

Jan. 14 1555 1655 1. 00 July 4 0637 0716 . 65

1658 1704 . 10

July 9 0708 718 . 17

Jan. 15 0822 0846 . 40 0832 0836 . 07

0850 0856 . 10

0901 0905 . 07 July 18 0708 0726 . 30

0744 0750 . 10

Feb. 5 0725 0759 . 57

0801 0805 . 07 July 19 0725 0730 . 08

0910 0927 . 28

Aug. 12 1805 1810 . 08

Feb. 7 2158 2204 . 10 1816 1819 . 05

2206 2227 . 35 1821 1826 . 08

1827 1829 . 03

Feb. 10 0716 0723 . 12 1830 1832 . 03

0724 0726 . 03 1842 1853 . 18

4* 0820 0825 . 08 1855 1912 . 28

1923 1930 . 12

Feb. 17 1754 1758 . 07 1934 1947 . 22

May 6 0657 0659 . 03 Aug. 13 1834 1835 . 02

0705 0707 . 03 1837 1838 . 02

0712 0731 . 32 1846 1848 . 03

0733 0735 . 03 1911 1915 . 07

0737 0743 . 10

Aug. 15 0723 0807 . 73

June 21 0717 0718 . 02 0819 0822 . 05

0921 0922 . 02

July 1 2324 2328 . 07

2332 2358 . 43 Aug. 17 1920 1921 . 02

1926 1927 . 02

July 2 0005 0010 . 08 1934 1935 . 02

0015 0020 o 00 0655 0728 . 57 Aug. 18 0725 0849 1. 40

0803 0807 . 07

0809 0834 . 42 Aug. 19 1849 1856 . 12

0837 0906 . 48 1906 1908 . 03

1949 1951 . 03 1909 1911 . 03

2007 2008 . 02 1914 1932 . 30
c
- 19 -

Table 3, cont’d.

3. c. cent’ d. DATE LOCAL TIME NIGHT DAY

1 907 Start Stop Hours Hours

Aug. 20 0749 0806 . 28

Aug. 21 0502 0521 . 32

0736 0840 1. 07

Aug. 22 0740 0758 . 30

0800 0817 . 28

0818 0824 . 10

0828 0835 . 12

Aug. 27 0744 0748 . 07

0835 0842 . 12

0843 0845 . 03

0846 0848 . 03

Sept. 3 0758 0804 . 10

0805 0810 . 08

0811 0814 . 05

0828 0834 . 10

0835 0839 . 07

0842 0844 . 03

0845 0846 . 02

2211 2217 . 10

2309 2315 . 10

Sept. 4 0009 0025 . 27

0200 0211 . 18

0220 0229 . 15

Sept. 6 0416 0421 . 08

0424 0435 . 18

0438 0446 . 13

0447 0501 . 23

0511 0515 . 07

0516 0537 . 35

0544

0718

0548

0722

. 07

. 07

0725 0744 . 32

07 55 0827 . 53

0832 0847 . 25

DATE LOCAL TIME NIGHT DAY

1967 Start Stop Hours Hours

Sept. 13 2302 2308 . 10

2332 2400 . 47

Sept. 14 0002 0013 . 18

0051 0056 . 08

0139 0204 . 42

0208 0216 . 13

0222 0314 . 87

07 56 1031 2. 58

1035 1046 . 18

Sept. 19 0640 0646 . 10

0649 07 50 . 02

Sept. 23 0528 0533 . 08

0806 0818 . 20

0833 0852 . 32

0902 0945 . 72

Sept. 26 1929 1931 . 03

2041 2042 . 02

2045 2047 . 03

2050 2051 . 02

2058 2108 . 17

2128 2142 . 23

2148 2218 . 50

2220 2245 . 42

Sept. 27 0028 0035 . 12

0037 0214 1. 62

0219 0220 . 02

0228 0238 . 17

0240 0241 . 02

0245 0247 . 03

0251 0255 . 07

0430 0605 1. 58

0728 0731 . 05

0809 1001 1. 87
4I
- 20 -

Table 3, cont’d.

3. c. comt’d.

DATE LOCAL TIME NIGHT DAY DATE LOCAL TIME NIGHT DAY

1967 Start Stop Hours Hours 1967 Start Stop Hours Hours

Sept. 29 1 553 1634 . 68 Nov. 1 0457 0531 . 57

1736 1750 . 23 0537 0547 . 17

0657 0749 . 87

Sept. 30 0530 0543 . 22 0951 0956 . 08

0957 1001 . 08

Oct. 8 0941 0949 . 13 1003 1015 . 20

0951 1002 . 18 1020 1025 . 08

1004 1006 . 03 2245 2258 . 22

1233 1235 . 03

1241 1246 . 08 Nov. 2 0419 0426 . 12

1250 12 51 . 02 0501 0504 . 05

1252 12 55 . 05 0543 0552 . 15

0557 0616 . 32

Oct. 10 1151 1154 . 05 0808 0902 . 90

1816 1824 . 13

Nov. 21 0648 0705 . 28

Oct. 12 0410 0413 . 05 0734 0736 . 03

0424 0427 . 05

1102 1104 . 03 Dec. 26 2247 2248 . 02

1107 1112 . 08 2325 2332 . 12

1133 1134 . 02 2337 2341 . 07

Oct. 19 2344 2400 . 27 Dec. 27 0145 0151 . 10

0226 0246 . 33

Oct. 20 0000 0005 . 08 02 50 0308 . 30

0052 0057 . 08 0316 0420 1. 07

0226 0353 1. 45 0513 0527 . 23

0415 0427 . 20 0726 07 57 . 52

0440 0448 . 13 0759 0807 . 13

0603 0606 . 05 0820 0825 . 08

0610 0644 . 57 0827 0845 . 30

0801 0950 1 . 82 1030 1032 . 03

0952 1101 1. 15 1035 1037 . 0.8 1221 1223 . 03

Oct. 22 0802 0810 . 13

Oct. 23 0240 0244 . 07

Oct. 2 5 9917 0920 . 05

- 21 -

3. c. cont’d.

Table 3, cont’d.

DATE LOCAL TIME NIGHT DAY

1967 Start Stop Hours Hours ^ Dec. 28 0530 0539 . 15

0541 0545 . 07

0732 0822 . 83

0823 0826 . 05

0832 0835 . 05

0838 0845 . 12

0852 0907 . 25

0954 0956 . 03

1000 1004 . 07

Dec. 29 0117 0122 . 08

0136 0202 . 43

0447 0505 . 30

0506 0510 . 07

0522 0529 . 12

0531 0545 . 23

&^

Total time for 1967 (hours) 19. 71 29. 84

Number of occurrences 83 119

Maximum duration (hours) 1. 62 2. 58

Mean duration (hours) 0. 24 0. 25

Median duration

0. 13 0. 08

* Combined Periods

Total time for 1967 (hours) 24. 59 35. 86

Number of occurrences 39 52

Maximumf duration (hours) 2. 45 3. 00

Mean duration (hours) 0. 61 0. 70

Median duration (hours) 0. 27 0. 57

* Combined periods containing conditions above the RVR level lasting less than 30 minutes

are considered as a single occurrence with the duration of the period extending from the

beginning of the first period to the end of the last period.
\
- 22 -

Table 3, cont’d.

3. d. Recapitulation, Periods of RVR below a Reported RVR of 1000 feet at Areata

Airport during 1965, 1966, and 1967

NIGHT (Hours) DAY (Hours)

1965 1966 1967 Period 1965 1966 1967 Period

Individual Occurrences

Total time (hours) 31. 19 4. 49 19. 71 55. 32 52. 15 35. 87 29. 84 117. 71

Number of occurrences 96 22 83 201 186 125 119 430

Maximum duration (hours) 2. 92 0. 62 1. 62 2. 92 3. 10 1. 70 2. 58 3. 10

Mean duration (hours) 0. 32 0. 22 0. 24 0. 28 0. 29 0. 29 0. 25 0. 27

**Median duration (hours) 0. 15 0. 16 0. 13 0. 15 0. 08 0. 10 0. 08 0. 08

^Combined Periods

Total time (hours) 38. 61 5. 83 24. 59 69. 03 65. 80 47. 59 35. 86 149. 25

Number of occurrences 50 16 39 105 48 41 52 144

Maximum duration (hours) 5. 07 0. 90 2. 45 5. 07 8. 32 5. 58 3. 00 8. 32

Mean duration (hours) 0. 77 0. 39 0. 61 0. 66 1. 26 1. 16 0. 70 1. 04

**Median duration (hours) 0. 38 0. 37 0. 27 0. 33 0. 76 0. 70 0. 57 0. 68

%

^Combined periods containing conditions above the RVR level lasting less than 30 minutes

are considered as a single occurrence with the duration of the period extending from the

beginning of the first period to the end of the last period.

§
I

(I
- 23 -

Table 4

4. a. Periods of RVR below a Reported RVR of 800 feet at Areata Airport during 1965.

(Based on runway lights operated at brightness step 5).

DATE LOCAL TIME NIGHT DAY DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours Hours 1965 Start Stop Hours Hours

Jan. 14 1123 1124 . 02 Feb. 18 0647 0652 . 08

0854 0934 . 67

Jan. 15 0743 0745 . 03 0936 0942 . 10

0746 07 52 . 10 0945 0952 . 12

0806 0807 . 02 1027 1028 . 02

0808 0816 . 13 1032 1033 . 02

0855 0940 . 75 1625 1626 . 02

1105 1108 . 03 1630 1632 . 03

1113 1119 . 10 1633 1636 . 05

1135 1145 . 17 1643 1700 . 30

1146 1152 . 10 1704 1735 . 52

1156 1201 . 08

1203 1210 . 12 Feb. 20 0658 0701 . 05

1211 1215 . 07 0754 0808 . 23

1223 1227 . 07 08 53 0906 . 22

1322 1327 . 08

July 28 0518 0519 . 02

Jan. 17 0148 0158 . 17 0526 0530 . 07

0536 0549 . 22

Jan. 30 1040 1114 . 57

Aug. 9 1826 1827 . 02

1227 1317 . 83

Aug. 11 0528 0538 . 17

Feb. 1 0658 0713 . 25 0540 0542 . 03

0733 0801 . 47 0548 0602 . 23

Feb. 2 1027 1044 . 28 Aug. 13 0533 0632 . 98

Sept. 21 0606 0801 1. 92

Sept. 23 0612 0613 . 02

0622 0623 . 02

0628 0753 1. 42

0802 0813 . 18

i

i
I

«ll
- 24 -

Tabid 4, cont’cl.

4. a. cont’d.

DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours Hours

Oct. 28 0755 0802 . 12

Oct. 29 0847 0934 . 77

0955 0957 . 03

Oct. 30 0908 0950 . 70

1023 1031 . 13

1739 1742 . 05

1743 1748 . 08

Total time for 1965 (hours) 0. 17 13. 88

Number of occurrences 1 54

Maximum duration (hours) - 1. 92

Mean duration (hours) - 0. 26

Median duration (hours) - 0. 12

^Combined Periods

Total time for 1965 (hours) 0. 17 17. 54

Number of occurrences 1 27

Maximum duration (hours) - 2. 37

Mean duration (hours) - 0. 67

Median duration (hours) -

0. 31

^Combined periods containing conditions above the RVR level lasting less than 30

minutes are considered as a single occurrence with the duration of the period extending

from the beginning of the first period to the end of the last period.

I

- 25 -

Table 4, cont’d.

4. b. Periods of RVR below a Reported RVR of 800 feet at Areata Airport during I960.

(Based on runway lights operated at brightness step 5).

DATE LOCAL TIME NIGHT DAY DATE LOCAL TIME NIGHT DAY

1966 Start Stop Hours Hours 1966 Start Stop Hours Hours

Apr. 15 0712 0734 . 37 Oct. 25 1735 0904 1. 48

0841 0844 . 05 1006 1012 . 10

1140 1155 . 25

Apr. 23 0547 0557 . 17 1215 1220 . 08

May 3 0547 0552 . 08 Nov. 2 0645 0756 1. 18

0801 0805 . 08

May 25 0624 0628 . 07 0810 0821 . 18

0630 0652 . 37 08 59 0903 . 07

0905 0907 . 03

Aug. 6 0622 0629 . 12 0915 0924 . 15

0702 0704 . 03 0927 0931 . 07

0708 0715 . 12 1037 1040 . 05

0725 0800 . 58 1106 1110 . 07

Aug. 16 062 5 0630 . 08

0653 0657 . 07

0702 0708 . 10

Sept. 4 0520 0643 1. 38

Sept. 5 0640 0821 1. 68

Sept. 21 0611 0624 . 22

Sept. 26 0554 0556 . 03

0658 0706 . 13

0708 0718 . 17

Oct. 23 1151 1157 . 10

Oct. 24 1034 1038 . 07

1049 1057 . 13
t*
- 26 -

Table 4, cont’d.

4. b. cont’d.

DATE LOCAL TIME NIGHT DAY

1966 Start Stop Hours Hours

Nov. 4 0720 0753 . 55

0801 0806 . 08

0916 0926 . 17

0930 1000 . 50

1002 1006 . 07

1007 1008 . 02

1011 1014 . 05

1017 1019 . 03

1046 1048 . 03

1049 1053 . 07

1054 1057 . 05

1058 1102 . 07

1106 1107 . 02

Total time for 1966 (hours) 0 12. 02

Number of occurrences 0 48

Maximum duration (hours) - 1. 68

Mean duration (hours) - 0. 24

Median duration (hours) - 0. 08

Combined Periods

Total time for 1966 (hours) 0 14. 62

Number of occurrences 0 23

Maximum duration (hours) - 1. 85

Mean duration (hours) - 0. 70

Median duration (hours) 0. 47

Combined periods containing conditions above the RVR level lasting less than 30

minutes are considered as a single occurrence with the duration of the period extending

from the beginning of the first period to the end of the last period.

- 27 -

Table 4, cont’d.

4. c. Periods of RVR below a Reported RVR of 800 feet at Areata Airport during 19(37.

(Based on runway lights operated at brightness step 5). DATE LOCAL TIME NIGHT DAY

1967 Start Stop Hours Hours

Feb. 5 0725 0757 . 53

Feb. 10 0719 0720 . 02

July 2 0719 0724 . 08

0812 0819 . 12

0837 0839 . 03

0848 0849 . 02

0853 08 54 . 02

July 4 0637 0642 . 08

Aug. 12 1816 1818 . 03

1822 1824 . 03

1828 1829 . 02

1847 18 50 . 05

1906 1908 . 03

Aug. 15 0738 0741 . 05

Aug. 18 0729 0730 . 02

0745 0751 . 10

0809 0815 . 10

0818 0819 . 02

0824 0826 . 03

Aug. 19 1915 1916 . 02

1920 192 5 . 08

Aug. 20 0749 07 53 . 07

Aug. 21 0728 0747 . 32

0748 0817 . 48

0818 082 5 . 12

0833 0834 . 02

DATE LOCAL TIME NIGHT DAY

1967 Start Stop Hours Hours

Sept. 6 0416 0420 . 07

0426 0432 . 10

0439 0445 . 10

0447 0449 . 03

0451 0456 . 08

0719 0721 . 03

0730 0744 . 23

0755 0757 . 03

0758 0825 . 45

0840 0841 . 02

Sept. 13 2348 2357 . 15

Sept. 14 0756 0800 . 07

0811 0915 1. 07

0919 0925 . 10

0931 0936 . 07

0948 1022 . 57

Sept. 23 0910 0933 . 38

Sept. 27 0049 0053 . 07

0055 0100 . 08

0116 0120 . 07

0435 0440 . 08

0457 0528 . 52

0809 0816 . 12

0830 0936 1. 10

Sept. 29 1608 1616 . 13

1617 1625 . 13

Sept. 30 0532 0542 . 17

Oct. 8 0946 0948 . 03

0956 1002 . 10

1242 1245 . 05

12 52 1254 . 03
I

/

' SB
- 28 -

Table 4, cont’d

# 4.c.. cont’d.

DATE LOCAL TIME NIGIIT DAY DATE LOCAL TIME NIGHT DAY

1907 Start Stop Hou rs Hours 1967 Sta rt Stop Hours Hour:

Oct. 10 1817 1820 . 05 Nov. 21 0650 0651 . 02

Oct. 20 0227 0235 . 13 Dec. 27 0345 0400 . 25

0240 0148 . 13 9726 0747 . 35

0249 02 54 . 08 0750 0753 . 05

0336 0353 . 28 0801 0803 . 03

0610 0620 . 17 0828 0844 . 27

0801 0842 . 68

0845 08 50 . 08 Dec. 28 0741 0742 . 02

0854 0856 . 03 0747 0749 . 03

0912 0913 . 02 0755 0759 . 07

0915 0916 . 02

0926 0931 . 08 Dec. 29 0151 0200 . 15

0932 0940 . 13 0449 0504 . 25

1016 1018 . 03 0507 0510 . 05

Nov. 1 0502 0503 . 02

0657 0747 . 83

22 52 2256 . 07

Nov. 2 0421 0423 . 03

0549 0551 . 03

0606 0608 . 03

0612 0615 . 05

0809 0837 . 47

0839 08 53 . 23

Total time for 1967 (hours) 3. 26 10. 67

Number of occurrences 25 64

Maximum duration (hours) 0. 52 1. 10

Mean duration (hours) 0. 12 0. 17

Median duration (hours) 0. 08 0. 07

Combined Periods

Total time for 1967 (hours) 4. 61 15. 80

Number of occurrences 16 25

Maximum duration (hours) 0. 38 2. 47

Mean duration (hours) 0. 29 0. 63

Median duration (hours) 0. 21 0. 38

*Combined periods containing conditions above the RVR level lasting less than 30

minutes are considered as a single occurrence with the duration of the period extending

from the beginning of the first period to the end of the last period.
<
- 29 - #

Table 4, cont’d

4.d. Recapitulation, Periods of RVR below a Reported RVR of 800 feet at Areata

Airport during 1965, 1966, and 1967

NIGHT (Hours) DAY (Hours)

1965 1966 1967 Period 1965 1 966 1967 Period

Individual Occurrences

Total time (hours) 0. 17 0 3. 26 3. 43 13. 88 12. 02 10. 67 36. 57

Number of occurrences 1 0 . 25 29 54 48 64 166

Maximum duration (hours) - - 0. 52 0. 52 1. 92 1. 68 1. 10 1. 92

Mean duration (hours) - - 0. 12 0. 12 0. 26 0. 24 . 17 ID. 22

Median duration (hours) - - 0. 08 0. 08 0. 12 0. 08 0. 07 0. 08

*Combined Periods

Total time (hours) 0. 17 0 4. 61 4. 78 17. 54 14. 62 15. 80 47. 96

Number of occurrences 1 0 16 17 27 23 25 74

Maximum duration (hours) - - 0. 88 0. 88 2. 37 1. 85 2. 47 2. 47

Mean duration (hours) - - 0. 29 0. 28 0. 67 0. 70 0. 63 0. 65

Median duration (hours) - - 0. 21 0. 17 0. 31 0. 47 0. 38 0. 52

Combined periods containing conditions abc’ve the RVR level lasting less than 30

minutes are considered as a single occurrence with the duration of the period extending from

the beginning of the first period to the end of the last period.
ii>
- 30 -

Table 5

Periods of RVR below a Reported RVR of 600 feet at the Areata Airport during

1965, 1966, and 1967

5. a. For 1965 5. b. For 1966 5. c. For 1967

DATE LOCAL TIME DAY DATE LOCAL TIME DAY DATE LOCAL TIME NIGHT DAY

1965 Start Stop Hours 1966 Start Stop Hours 1967 Start Stop Hours Hours

Jan. 30 1242 1243 . 02 Sept. 4 0523 0643 1. 33 Feb. 5 0730 0756 . 43

Feb. 18 1714 1717 . 05 Sept 26 0650 0700 0. 17 Sept. 6 0444 0445 . 02

July 28 0518 0520 . 0.3 Oct. 2 5 0654 0712 0. 30 Nov. 1 0659 0745 . 77

0715 0717 0. 03

Aug. 13 0539 0 541 . 03 0724 0758 0. 57 Dec. 27 0728 0731 . 05

1048 1049 0. 02

Sept. 21 0625 0627 . 03

0731 0735 . 07 Nov. 2 0645 0722 0. 62

0740 0745 0. 08

Sept. 23 0635 0636 . 02 0748 0749 0. 02

0642 0644 . 03

0659 0707 . 13 Nov. 4 0732 0738 0. 10

0709 0713 . 06

Oct. 30 0610 0628 . 30

(1965) (1966) (1967)

5. d. Recapitulation, Periods of RVR below a Reported RVR of 600 feet at Areata

Airport during 1965, 1966, and 1967.

NIGHT (Hours) DAY (Hours)

1965 1966 1967 Total 1965 1966 1967 Total

Total time (hours) - 0. 02 0. 02 0. 77 3. 24 1. 25 5. 26

Number of occurrences - 1 1 11 10 3 24

Maximum duration (hours) - - - 0. 30 1. 33 0. 77 1. 33

Mean duration (hours) - - - 0. 07 0. 32 0. 42 0. 22

Median duration (hours) - - - 0. 03 0. 13 0. 43 0. 07

* Combined Periods

Total time (hours) - 0. 02 0. 02 1

-L. 15 3. 76 1. 25 6. 16

Number of occurrences - 1 1 8 6 3 17

Maximum duration - - 0. 02 0. 63 1. 33 0. 77 1. 33

Mean duration (hours) - - 0. 02 0. 14 0. 63 0. 42 0. 36

Median duration (hours) - - 0. 02 0. 04 0. 62** 0. 43 0. 10

^Combined periods containing conditions above the RVR level lasting less than 30 minutes

are considered as a single occurrence with the duration of the period extending from the

beginning of the first period to the end of the last period.

**Three periods had a duration of 0. 17 or less and three periods had durations of 1. 07 or more.

-31 -

Table 6

Minimum Value of RVR’ s during Periods of RVR below a Reported RVR of 600 feet

at Areata Airport during 1965, 1966, and 1967

Time for Period Time of Minimum Minimum Minimum

Below 600 Feet RVR Condition Transmittances RVR

DATE START STOP START STOP T

500

FEET

1965

Jan. 30 1242 1243 1242 1243 <. 001 <505

Feb. 18 1714 1717 1714 1717 0. 0001 ( 2) 410

July 28 0 518 0520 0519 0520 . 0004 * 2) 460

Aug. 13 0539 0541 0539 0540 . 0005^ 470

Sept. 21 0625 0627 0625 0627 (1)

. 0006 J

'

. 0004 (1)

480

0632 0635 0632 0635 460

Sept. 23 0635 0636 0635 0636 . 0004

. 0006

. 0008

(1)

460

0642 0644 0642 0644 480

0659 0707 0700 0707 480

0709 0713 0711 0713 490

Oct. 30 0610 0628 0613 0617 . 0003

^

450

1966

9006

(2)

. 0006 (2)

Sept. 4 0523 0643 0600 0605 480

0630 0640 480

Sept. 26 0650 0700 0651 0658 . 0003 (5) 450

Oct. 25 0654 0712 0656 0700 . 0004 5®}

• 0007 t! .0003

4 >

. 0006

460

0715 0717 0716 0717 490

0724 0758 0727 0730 450

1048 1049 1048 1049 480

Nov. 2 0645 0722 0700 0705 . 000036 (5) 370

0740 0745 0740 0743 • 0005 (5)

(4)

. 0003 v ' 470

0748 0749 0748 0749 450

Nov. 4 0732 0738 0732 0738 (1)

. 0004 v ' 460
{
- 32 -

Table 6, cont’d.

Time for Period Time of Minimum Minimum Minimum

Below 600 Feet RVR Condition Transmittances RVR

DATE START STOP START STOP T

500

FEET

19G7

Feb. 5 0730 0756 0749 07 51

(4)

. 00006 v ' 390

Sept. 6 0440 0445 0444 0445 . oooooi 480 (Night-

(4)

. 000006

time)

Nov. 1 0659 0745 0711 0727 325

Dec. 27 0728 0731 0728 0731 . 000008 330

( 1 ) Pulse count from records of 500-foot baseline transmissometer, fair accuracy.

( 2 ) Pulse count from 500-foot baseline transmissometer estimated from records of

poor quality.

(3) Below minimum useful range of 500-foot baseline transmissometer.

(4) Pulse count and readings from records of 250 -foot baseline transmissometer, good

accuracy.

(5) Readings and pulse counts from records of 250-foot baseline transmissometer, fair

accuracy.
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- 33 - #

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- 39 -

4. SUMMARY OF FAA OBSERVATIONS

The FAA Flight Service Station (FSS) WBAN-10 observations for the period from

1962 through 19G7 for the Areata Airport are summarized in table 7. Both ceilings

and visibilities are included in this summary. The total hours during which

visibility was below 1/4, 1/2, 1, 2, and 3 miles and during which the ceiling was

below 100, 200, 300, 50Q, and 800 feet are reported here. The number of days of

each year during which these conditions occurred are indicated. The observations

were made by the FSS communicators on duty as part of the hourly and special

weather observations. The reported condition may have been determined from

personal observation, instrument reading, or pilot report. Observations are reported regularly each hour and special observations are required for changes at specified levels. Other specials may be made when significant changes in conditions occur even though these observations are not specifically required. Often the times

of change from one interval to the next cannot be determined accurately. In these

instances the time for the change was estimated to the nearest quarter hour.

Conditions lasting for less than 15 minutes were unlikely to be reported. As is

evident from the data there is a fairly close relationship between ceiling and

visibility at Areata.

5. DISCUSSION

The several summaries presented in this report are based on different criteria

and are not suitable for direct comparison with each other. From the different

summaries, information on the occurrence of fog conditions at Areata ranging

from three miles visibility down to 600 feet RVR can be obtained. The amounts

by year, month, and day or night may be especially helpful in scheduling projects or for determining of conditions suitable for given tests are likely to occur. Data

similar to that given in these summaries will continue to be reported at intervals

in the Quarterly Progress Reports.

USCOMM-DC—NHS
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