mounted, or at least equipped with sledge-like
pilots who use the runway in order to obtain an
bottoms.
accurate picture of the range of tolerance and
Runway markers and flag lines also provide a
desires. The surface features that we found to be
collection site for snow. Markers should be kept
of most concern to aircraft personnel include the
to an absolute minimum. Snow that does collect
very short wavelength smoothness (frequency on
around flag lines and markers should be removed
the order of 110 cm), coefficient of surface fric-
or spread so that these obstacles do not become
tion, and the ability to visually distinguish the
surrounded by an "island of snow." This will
runway surface (surface definition).
lead to accelerated snow drifting in the future.
The process of grading will leave the ice with a
We used drags and planes to keep the snow along
rough surface when viewed on a small scale (Fig.
the flanks of the runway shaped to limit drifting,
38, 47). Tires traveling over this surface at high
including close attention to the area around mark-
speed will produced a vibration and noise that
ers and flags. Operators could only get within a
we found was undesirable to some of the (L)C-
few meters of these obstacles using heavy equip-
130 flight crews. A thin cover of snow, even if it is
ment, so we cleaned around the flags and mark-
uncompacted, will alleviate this problem. A thin
ers with hand shovels before using large devices.
cover of snow is also useful as a "wearing sur-
If snow accumulation is not desired, scarps or
face" for the runway. Dirt, exhaust soot, tire wear
sharp elevations changes should be avoided be-
dust (from takeoffs and landings on paved run-
tween snow and ice or anywhere on the snow
ways), and any other spilled or dropped contami-
surface in the immediate vicinity of the runway.
nants can be easily removed when deposited on
These will fill with snow and a drift may extend
the wearing surface and fresh snow added. How-
for as much a 10 times the height of the scarp.
ever, the thin snow cover should never exceed a
depth of 6 cm to avoid overstressing landing gear.
It is best to drag or plane this wearing surface
once a day or after every aircraft operation to
RUNWAY SMOOTHNESS,
remove any tire tracks.
SURFACE DEFINITION, AND
At natural blue-ice sites, the completely ex-
FRICTION COEFFICIENT
posed glacial ice often has a cuspate surface as the
Feedback from flight crews will provide the
result of ablation (Fig. 74). This type of surface
most useful information on the integrity of the
will generate noise and high frequency vibration
runway surface. Maintenance personnel should
in fast-moving aircraft but this is nearly unavoid-
establish frequent communication with all of the
able. Moving snow to the runway to fill the cusps
Figure 74. Exposed ice (blue ice) at inland locations.
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