surface will collapse. In areas where this hap-
tion and intensity of solar/air-temperature peak,
pens, it is generally too late to avoid heat buildup
and 6) probability of snowfall based on historical
in the ice. Recovering the areas with fresh snow is
data. Frequent dragging and planning of the run-
the only option at this point, and even that may
way snow cover will ensure a highly reflective
not be enough to prohibit a 3 to 5C jump in ice
surface but will speed evaporative losses. This
temperature.
can be used to advantage to protect the ice from
We found that snow planes and drags do a
melt feature development, while at the same time
good job of keeping the surface roughened and
minimizing the amount of snow to be removed
permeable. These devices essentially stir the very
mechanically once the critical period has passed.
top of the surface and leave it with a reflectance
If it appears that the snow cover present on the
ratio of as much as 85%. This surface processing
runway is only marginally enough to provide the
will slightly increase the rate of loss of snow cover
protection required, one should settle for snow
due to ablation, but this loss rate is much less, and
surface grooming every second or third day, with
is more manageable than, the rate of loss due to
the resulting gradual drop in reflectance during
subsurface melting in the snow that can occur if
these few days. This latter sequence will limit
the surface is not treated. During the peak of solar
snow loss while maintaining a minimal degree of
intensity and air temperature, the Pegasus run-
reflectance. In either case, constant attention to
way snow surface needed treatment at least ev-
the runway is required by experienced runway
ery other day, sometimes daily. Also at this time
maintenance personnel. Data on how tempera-
in the season, grooming works best late in the
tures are fluctuating during the day and cumula-
coolest part of the day (generally after midnight
tive seasonal ice and air temperature, incoming
and before 5:00 a.m.). Snow loss is minimized by
radiation levels, and snow cover density, thick-
working the surface when the sun angle is low
ness, and composition must be compared each
and the air temperature has already reached its
day to make informed decisions about mainte-
daily minimum. In addition to minimizing snow
nance activities.
loss by working at this time of day, damage to the
surface caused by the towing machinery will also
Removal of protective snow cover
be limited.
The protective snow cover may be removed as
Snowfall during the peak temperature/solar in-
soon as conditions allowing the formation of melt
tensity period can occur at some sites. These snows
features have passed. The determination of this
are often made up of large flakes that fall gently
point in time was discussed at the beginning of
onto the surface. Such snow has a very high reflec-
this section. Our experience has been that almost
tance ratio and can provide a great boost in pro-
no snow loss occurs on a maintained cover. If not
tection of the ice runway. This may be an
maintained, snow loss through ablation and melt-
advantage or disadvantage, depending on the
ing will be concentrated in various locations and
amount of snow needed and the amount present
will accelerate rapidly out of control.
on the runway. During the 199293 summer, a light,
If more than 15 cm of snow needs to be removed
fluffy snow fell during very calm weather at the
from the runway, a two-stage process should be
Pegasus site approximately once per week. This
used. In this case, the first layer removed should
slowed the ablation process and the net loss of
be about 10 cm and stripping should start from
material from the runway's protective cover was
the outside edges of the runway and work to-
almost nil. Without great confidence in the ability
ward the centerline. At Pegasus we used the
to predict snowfall during this period at a given
grader to peel off and windrow the top layer of
runway site, we do not rely on summer snowfalls
snow by extending the skids at either end of the
when planning for the protection of the runway.
grader blade so that they could penetrate the pro-
The goal of maintenance activities should be to
tective snow cover and follow the ice surface (Fig.
provide a highly reflective and permeable surface
80). The snowblower was capable of operating on
during the critical period when air temperature
the freshly graded snow surface to remove the
and solar intensity are at their peak. Surface main-
windrow snow to the sides of the runway.
tenance procedures should be governed by 1) re-
The second stage of stripping, or the only stage
flectance ratio readings on the runway, 2) net
necessary if less than 15 cm of snow were present,
thickness of protective snow cover, 3) position
will remove all but 45 cm of snow from the ice
within critical warm period cycle, 4) temperature
surface. This stripping should proceed from the
profile within the runway ice, 5) expected dura-
centerline outward toward the edges of the run-
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