TM 5-826-6/AFR 93-5
Figure A-65. High severity swell.
(3) Measuring procedure. The surface area of the swell is measured in square feet. The severity rating should
consider the type of pavement section (i.e., runway, taxiway, or apron). For example, a swell of sufficient magnitude to
cause considerable roughness on a runway at high speeds would be rated as more severe than the same swell located on
an apron or taxiway where the normal aircraft operating speeds are much lower. The following guidance is approved for
runways:
Severity
Height Differential
L
< 3/4 inch
M
3/4 - 1/2 inch
H
> 1-1/2 inch
q. Blowup, distress 61.
(1) Description. Blowups occur in hot weather, usually at a transverse crack or joint that is not wide enough to
permit expansion of the concrete slabs. The insufficient width is usually caused by infiltration of incompressible materials
into the joint space. When expansion cannot relieve enough pressure, a localized upward movement of the slab edges
(buckling) or shattering will occur in the vicinity of the joint. Blowups can also occur at utility cuts and drainage inlets. This
type of distress is almost always repaired immediately because of severe damage potential to aircraft. The main reason
blowups are included here is for reference when closed sections are being evaluated for reopening.
(2) Severity levels.
(a) Low severity level (L). Buckling or shattering has not rendered the pavement inoperative, and only a
slight amount of roughness exists (fig. A-66). Note that this would only be considered low severity if the shattering in the
foreground was the only part existing and the foreign material removed.
A-38
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