Pavements Survey

The bearing capacity of an airport pavement is not something you measure once. It changes over time under load cycles, weather and the evolution of traffic. Knowing it accurately is first of all a matter of operational safety, but it is also the basis on which maintenance decisions are made: planned intervention based on reliable data costs a fraction of an unplanned closure of a runway or apron.

Since 28 November 2024 the reference is ACR/PCR

Through Amendment 15 to Annex 14, Volume I, ICAO replaced the ACN/PCN method with the ACR/PCR method — Aircraft Classification Rating and Pavement Classification Rating. Adopted in 2020 and effective from July of that year, it became mandatory on 28 November 2024 after a four-year transition period. The ACN/PCN method, in use since 1981, is no longer the reference standard for publishing pavement strength in the AIP.

The change is not merely one of terminology. The new method is based on layered elastic analysis, adopts standard subgrade categories for both flexible and rigid pavements, and eliminates the alpha factor and the layer equivalency factors that had made ACN/PCN increasingly inconsistent with modern pavement design methods.

Two practical consequences deserve attention. First, ACR and PCR values are approximately one order of magnitude higher than the corresponding ACN and PCN values. There is no direct conversion between the two systems, and comparing a legacy PCN with a new ACR produces meaningless results. Second, ICAO does not prescribe a single calculation procedure for the PCR, but requires the determination to be based on the Cumulative Damage Factor (CDF) concept. The reporting format remains standardised, with the numerical value followed by four coded letters.

The ACR calculation procedure is described in ICAO Doc 9157, Aerodrome Design Manual — Part 3 “Pavements”, third edition. In the United States the FAA adopted the new method through Advisory Circular AC 150/5335-5D and the FAARFIELD 2.0 software.

More than a year after it came into force, the transition remains incomplete: several States have not published PCR values in their AIPs and are not compliant with ICAO Standards. For many airport operators the update is still an outstanding obligation, and postponing it means continuing to publish a figure that no longer reflects the reference standard. We support operators through this transition, from survey planning to a value ready for publication.

When a bearing capacity evaluation is required

Determining bearing capacity is required in four main circumstances:

• on a newly constructed pavement, to establish the value to be published in the AIP;
• periodically, to keep the published figure up to date;
• after major maintenance works, to reclassify the pavement;
• when signs of deterioration appear, to assess residual capacity and remaining service life.

How the survey is carried out

The evaluation is based on a combination of non-destructive tests, calibrated to the quantity and quality of data already available.

Ground penetrating radar and coring

Where the composition and thickness of existing layers are not known with certainty — a common situation on infrastructure built in successive phases — the investigation begins with a ground penetrating radar (GPR) survey, normally combined with sample coring for point validation and laboratory testing of materials.

HWD dynamic load testing

Once materials and thicknesses are known, Heavy Weight Deflectometer testing reproduces load cycles comparable to actual aircraft loading. The measured deflections yield the elastic moduli of the layers, the data required to determine bearing capacity and residual service life. Tests are run along multiple alignments, so the result is representative rather than localised.

Subgrade characterisation

DCP testing allows in-situ CBR evaluation, while LWD testing verifies granular base layers. Laboratory analysis completes the picture with water content, plasticity and other physical properties of the soil.

Surface surveys

Longitudinal profiling documents roughness and surface irregularities, while topographic survey and high-throughput video inspection map the crack pattern and georeference it in a GIS environment.

From survey to published value

Test results, generally numerous, are processed to determine the representative value to be adopted as reference. Under the ACR/PCR method the processing is based on the accumulated damage produced by actual and expected traffic, and returns a PCR in the coded format prescribed by ICAO, ready for publication in the AIP.

The same calculation framework allows pavement and fleet compatibility to be verified: comparing the aircraft ACR at operating weight with the pavement PCR establishes whether operations can proceed without restriction, or what weight or frequency limitations apply.

Pavement Management System

By the time cracking and deformation appear, it is usually too late for effective maintenance: only local, temporary fixes remain possible. An Airport Pavement Management System is designed to reverse this logic, planning maintenance before deterioration sets in.

The framework works in three stages: systematic collection and recording of pavement condition data; analysis and definition of a maintenance plan for each homogeneous section; periodic monitoring at a frequency proportional to traffic. The result is a predictive approach that prevents service disruption rather than reacting to it.

Our service

Air Alliance supports airport operators and authorities across the full cycle: survey campaign planning, supervision of site testing, data processing, determination of the bearing capacity classification and set-up of the Pavement Management System. Non-destructive testing is carried out with specialist partners.