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are poor (Chapter 10, 10.2.6); and
d) determine the fiction of paved runways that become
slippery under unusual conditions (Chapter 2, 2.9.8).
7.2 Runways should be evaluated when first constructed
or after resurfacing to determine the wet runway surface
fiction characteristics. Although it is recognized that fiction
reduces with use, this value will represent the fiction of the
relatively long central portion of the runway that is uncontaminated
by rubber deposits from aircraft operations and is therefore
of operational value. Evaluation tests should be made on
clean surfaces. If it is not possible to clean a surface before
testing, then for purposes of preparing an initial report a test
could be made on- a portion of clean surface in the central part
of the runway.
7.3 Friction tests of existing surface conditions should be
taken periodically in order to identify runways with low
friction when wet. A State should define what minimum
friction level it considers acceptable before a runway is
classified as slippery when wet and publish this value in the
State's aeronautical information publication (AIP). When the
fiction of a runway is found to be below this reported value,
then such information should be promulgated by NOTAM.
The State should also establish a maintenance planning level,
below which, appropriate corrective maintenance action
should be initiated to improve the friction. However, when the
friction characteristics for either the entire runway or a portion
thereof are below the minimum friction level, corrective
maintenance action must be taken without delay. Friction
measurements should be taken at intervals that will ensure
identification of runways in need of maintenance or special
surface treatment before the condition becomes serious. The
time interval between measurements will depend on factors
such as: aircraft type and frequency of usage, climatic conditions,
pavement type, and pavement service and maintenance
requirements.
7.4 For uniformity and to permit comparison with other
runways, fiction tests of existing, new or resurfaced runways
should be made with a continuous fiction measuring device
provided with a smooth tread tire. The device should have a
capability of using self-wetting features to enable measurements
of the fiction characteristics of the surface to be made
at a water depth of at least 1 mm.
7.5 When it is suspected that the friction characteristics of
a runway may be reduced because of poor drainage, owing to
inadequate slopes or depressions, then an additional test
should be made, but this time under natural conditions representative
of a local rain. This test differs from the previous
one in that water depths in the poorly cleared areas are
normally greater in a local rain condition. The test results are
thus more apt to identify problem areas having low fiction
values that could induce aquaplaning than the previous test. If
circumstances do not permit tests to be conducted during
natural conditions representative of a rain, then this condition
may be simulated.
25/11/04 ATT A-6
Attachment A Annex 14 -Aerodromes
7.6 Even when the fiction has been found to be above
the level set by the State to define a slippery runway, it may
be known that under unusual conditions, such as after a long
dry period, the runway may have become slippery. When such
a condition is known to exist, then a friction measurement
should be made as soon as it is suspected that the runway may
have become slippery.
7.7 When the results of any of the measurements
identified in 7.3 through 7.6 indicate that only a particular
portion of a runway surface is slippery, then action to
promulgate this information and, if appropriate, take corrective
action is equally important.
7.8 When conducting fiction tests on wet runways, it is
important to note that, unlike compacted snow and ice conditions,
in which there is very limited variation of the fiction
coefficient with speed, a wet runway produces a drop in fiction
with an increase in speed. However, as the speed increases, the
rate at which the fiction is reduced becomes less. Among the
factors affecting the friction coefficient between the tire and the
nmway surface, texture is particularly important. If the runway
has a good macro-texture allowing the water to escape beneath
the tire, then the fiction value will be less affected by speed.
Conversely, a low macro-texture surface will produce a larger
drop in friction with increase in speed. Accordingly, when
testing runways to determine their friction characteristics and
　
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