That is the current smoothness acceptance criterion as stated in the FAA’s Advisory Circular FAA AC 150/5370-G for initial pavement smoothness. It may tell you a good deal about construction quality, but what can it tell you about aircraft ride quality?
To get to the truth of a pavement’s ride quality, APR uses a variety of straightedge lengths. Initially, APR will use a short straightedge to compare the profile to standardized specifications such as the FAA’s Advisory Circular 150/5370-G or ICAO’s Annex 14. Typical in-use pavements exceed these relatively small deviations fairly frequently. These shorter straightedge evaluations are effective for evaluating pavement for smoothness, but not necessarily roughness – roughness that produces unwanted aircraft responses.
To find roughness that produce excessive aircraft response, APR uses longer straightedge lengths with large deviations. APR will use straightedge lengths that are more representative of a commercial aircraft’s wheel base (as measured from nose gear to main gear). This process will identify those deviations that actually create poor aircraft response and produce pilot and passenger complaints.
To the right are two straightedge plots of an in-service runway with a known roughness area. The first plot shows the results of a 12-foot straightedge analysis as called for by the FAA AC 150/5370-10G. The second plot is the same runway being evaluated using a longer straightedge length and a 1-inch (2.54cm) allowable deviation.