The surface area of the swell is measured in square feet (square meters). The severity rating should consider the type of pavement section (that is, 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.
For short wavelengths, locate the highest point of the swell. Rest a 10-ft (3-m) straightedge on that point so that both ends are equal distance above pavement. Measure this distance to establish severity rating.
The following guidance is provided for runways:
|
Severity |
Height Differential |
|
L |
< 3/4 in. (<20 mm) |
|
M |
3/4 to 1 ½ in. (>20 to 40 mm) |
|
H |
>1 ½ in. (>40 mm) |
Rate severity on high-speed taxiways using measurement criteria provided above. Double the height differential criteria for other taxiways and aprons.