allowable standards for military aircraft. A snowblower was used to remove graded
ice from the runway. Grading and clearing were completed at the end of October.
Protection during peak solar period
During December and the first half of January, relatively high temperatures (near
melting) and intense (24-hour/day) sunshine predominate in McMurdo. Under such
conditions, exposed ice absorbs radiation and often reaches the melting point. Melt-
ing may take place either on the surface or at a level slightly below the top of the ice.
Melting can often become widespread and can create very large meltpools that could
destroy the possibility of using a runway before complete refreezing in March or
later.
To protect against melting, the graded ice surface is covered with a 10-in. (25-cm)
layer of snow. Material from along the sides of the runway or overwinter snow present
on the runway provides the source for this cover. This protective snow cover must
be in place by the end of November, just prior to the peak of the austral summer.
Throughout December and the first week of January, the snow cover requires
some compaction, accomplished with heavy, rubber-tired rollers. Planing and drag-
ging is also done to assist in preserving the snow and to provide a highly reflective,
porous surface. Measurement of air, snow, and subsurface ice temperatures, together
with the intensity of the incoming solar radiation, is done to monitor snow cover
performance. Processing activities on the snow cover are governed by these mea-
surements to ensure that melting of the shelf ice does not occur.
Sometime between 7 and 15 January, the air temperature usually begins its down-
ward trend. Within several days of the onset of cooling the average daily air tem-
perature drops below the highest measured runway ice temperature. With the annual
cooling trend thus established, the protective snow cover can be stripped from the
runway.
Certification of runway strength
In preparation for wheeled Hercules operations at the end of the 1992-93 season,
the integrity of the runway was tested with a proof roller. The cart replicated the
main landing gear of a C-130 and was ballasted to a level more than 30% greater
than the maximum allowable load for each tire. The runway was tracked with the
proof roller with more extensive coverage along the central 100 ft (30.5 m). Total
coverage of the runway by the proof roller tires amounted to close to 50% of the
surface.
Approximately 30 weak spots were found by the proof roller. In these locations,
the ice failed by crumbling, leaving a slight depression in the surface. Excavation of
failed points revealed that they had an average size of 30 ft2 (2.8 m2) and were 618 in.
(1546 cm) deep. In nearly every case, failure points were associated with a thin
(0.25- to 0.5-in., 0.6- to 1.2-cm) gap. This gap was most likely caused during refreez-
ing of meltpools that were known to have been present at this site during the 1991
92 summer season.
Each failure point was excavated and all of the fractured ice around the edges was
dislodged. The ice chunks were broken into fist-sized pieces and packed into the
cavity. Cold water was then used to flood the cavity, making an ice bath that froze
completely within 48 hours. Numerous patched spots were re-proof-tested and all
were found to be sound. The runway was therefore certified for operation of wheeled
Hercules aircraft.
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