A runway can look like an enormous slab of concrete or asphalt, yet its ability to support an aircraft is not determined by appearance alone. Beneath the visible surface are pavement layers and supporting soil that respond to repeated wheel loads. For international reporting, the current ICAO method compares an aircraft’s structural demand with the reported structural capacity of the pavement using two values: Aircraft Classification Rating, or ACR, and Pavement Classification Rating, or PCR. The FAA’s active Advisory Circular 150/5335-5D implements this ICAO ACR-PCR method for reporting the strength of runways, taxiways and aprons in the United States. [1]
The basic comparison is deliberately simple at the operational level: an aircraft with an ACR equal to or below the reported PCR is structurally compatible with that pavement, subject to the tyre-pressure limitation and any other published operating restriction. If the aircraft’s ACR exceeds the pavement PCR, that does not automatically mean physical failure will occur on the next movement; it means the movement falls outside the normal unrestricted ACR-PCR comparison and requires assessment or permission under the responsible aerodrome authority’s procedures. FAA aeronautical-information guidance explicitly states that prior permission is required when an aircraft’s ACR exceeds the published PCR or its tyre pressure exceeds the published limit. [2]
Why pavement strength needs a standard language
An airport pavement is subjected to repeated loading rather than one isolated static weight. The load reaches the pavement through the aircraft’s tyres, landing-gear geometry and individual wheel loads. A heavy aircraft with many wheels can distribute load differently from a lighter aircraft with fewer or differently spaced wheels. Pavement response also depends on whether the structure is flexible or rigid and on the stiffness of the supporting subgrade. A simple maximum-aircraft-weight sign therefore cannot describe the entire structural interaction. The ACR-PCR method standardises that interaction into aircraft and pavement ratings that can be published and compared. [3]
The FAA describes ACR-PCR as the standardised ICAO method for reporting airport pavement strength and provides its FAARFIELD software for calculating ACR and PCR values. The method applies to paved runways, taxiways and aprons. This matters because the load-bearing question does not end after touchdown: an aircraft also has to taxi, turn and park on surfaces whose pavement structures may differ from the runway. [1]
From ACN-PCN to ACR-PCR
For decades, international aerodrome pavement strength was commonly published using Aircraft Classification Number and Pavement Classification Number — ACN and PCN. ICAO adopted the replacement ACR-PCR method in 2020 through Amendment 15 to Annex 14, Volume I. ICAO regional implementation material states that, following a four-year transition, ACR-PCR became applicable globally on 28 November 2024, replacing ACN-PCN as the current international reporting method. [4]
The change was not merely a new set of letters. FAA pavement research material says ACR retains the same broad purpose as ACN but modernises the engineering model. Among the changes, both rigid and flexible pavement structures are treated using layered-elastic analysis; the four standard subgrade categories are retained but defined through elastic modulus; flexible-pavement ACR calculations consider all wheels in the main landing gear; and the standard tyre pressure used in the calculation was increased to 1.5 MPa. [5]
What the Aircraft Classification Rating represents
The ACR represents the relative pavement effect of a particular aircraft at a defined weight and on a defined standard subgrade category. It is aircraft-specific because the calculation has to account for the landing-gear arrangement and loading that transfer force into the pavement. The same aircraft type can therefore have different relevant ACR values when operating at different weights or when considering different pavement/subgrade conditions. The ACR is not simply a repackaged maximum take-off weight. [3]
The FAA’s ICAO-ACR software calculates ACR values for aircraft operating on both flexible and rigid pavement. The FAA notes that the method uses all main-landing-gear wheels when calculating flexible-pavement ACR, one of the technical changes from the former ACN methodology. The objective is to produce a rating that reflects the structural demand generated by the aircraft’s actual wheel configuration within the standardised pavement model. [5]
What the Pavement Classification Rating represents
The PCR is the corresponding rating assigned to the pavement. It represents the structural capacity that the airport is reporting for unrestricted operations under the ACR-PCR system. Determining a PCR is more complex than measuring pavement thickness and converting it through a single table. The evaluation considers the pavement structure, material properties, subgrade and the aircraft traffic mix that the pavement is expected to support. ICAO’s Airport Pavement Strength Rating training specifically describes PCR determination as a calculation for a given pavement structure and aircraft mix in accordance with the Aerodrome Design Manual, Part 3. [6]
FAA AC 150/5335-5D provides procedures for calculating and reporting the value and directs users to FAARFIELD for pavement analysis. The FAA also maintains separate pavement-design and evaluation guidance in AC 150/5320-6G. That separation is important: PCR is a reporting value derived from engineering evaluation; it is not itself a substitute for the complete pavement-design process or pavement-management programme. [1] [7]
How to read a PCR code
A published PCR is more than one number. FAA aeronautical-information material describes it as a five-part code. A typical format might be written as PCR 460 R/B/W/T. Each part describes a different aspect of the pavement report: the numerical PCR value, the pavement type, the subgrade-strength category, the maximum authorised tyre-pressure category and the method used to evaluate the pavement. [2]
The first element is the PCR number itself. FAA guidance states that an aircraft with an ACR equal to or less than the published PCR can operate on that pavement subject to the tyre-pressure limitation. This numerical comparison is the central operational rule. However, the letters following the number cannot be ignored because they describe the assumptions and constraints associated with the rating. [2]
R or F: rigid versus flexible pavement
The second part of the code identifies pavement type. R means rigid pavement and F means flexible pavement. In broad structural terms, a rigid pavement relies substantially on slab action — typically a cement-concrete structural layer — to distribute wheel loads, whereas flexible pavement uses multiple bound and unbound layers whose response differs under loading. The ACR-PCR calculation therefore distinguishes the two pavement families rather than assuming an aircraft creates the same structural response in each. [2] [7]
The pavement-type letter is not a visual judgement about whether the top surface appears black or grey. A pavement can contain rehabilitation layers and complex structures, and structural classification must come from the aerodrome’s engineering records and evaluation. The ACR-PCR value is therefore published from an engineering assessment rather than inferred by a flight crew from what the pavement looks like. [3]
A, B, C or D: the subgrade category
The next letter identifies the standard subgrade category: A for high, B for medium, C for low and D for ultra-low subgrade strength. The subgrade is critical because pavement layers ultimately transmit load into the underlying ground. A pavement built over a strong supporting foundation behaves differently from an otherwise similar structure over a weak subgrade. [2]
FAA research material notes an important ACR-PCR change: the four categories remain, but they are defined using elastic modulus rather than the CBR or k-value relationships used in the legacy method. This aligns the classification with the layered-elastic modelling used by the newer system. The letter does not mean the entire airport sits on one uniform soil type; it is the category associated with the structural evaluation for the pavement being reported. [5]
W, X, Y or Z: the tyre-pressure limit
The fourth element reports the permitted tyre-pressure category. FAA guidance identifies W as unlimited; X as high, limited to 254 psi (1.75 MPa); Y as medium, limited to 181 psi (1.25 MPa); and Z as low, limited to 73 psi (0.50 MPa). Tyre pressure matters because wheel load is applied over a finite contact area and high local pressures can affect pavement materials even where the overall structural rating appears adequate. [2]
This is why comparing only ACR and PCR is insufficient. FAA guidance says prior permission is required not only when ACR exceeds PCR but also when aircraft tyre pressure exceeds the published pavement limit. An aircraft could therefore have a numerically acceptable ACR yet still require consideration because its tyre pressure does not comply with the reported pressure category. [2]
T or U: how the pavement was evaluated
The final letter indicates the evaluation method. T means technical evaluation and U means evaluation based on experience of aircraft using the pavement. A technically derived value can use pavement structural information, material properties and analytical tools such as FAARFIELD. An experience-based value reflects demonstrated operations rather than a full technical structural evaluation. The code therefore tells the user not only the reported capacity but how that capacity was established. [2] [1]
Why aircraft weight alone is not enough
Two aircraft at the same gross weight can place different demands on a pavement because landing-gear geometry determines how the load is divided and how stress fields overlap within the structure. Wheel spacing, number of wheels and individual wheel load all matter to pavement response. The ACR method addresses this by calculating the aircraft’s pavement effect rather than assigning the rating from gross weight alone. FAA’s ACR software explicitly models aircraft on rigid and flexible pavements under the ICAO method. [5]
The operating weight also changes from flight to flight. A long-haul aircraft at a high departure mass normally imposes greater wheel loads than the same aircraft after burning a substantial quantity of fuel. A pavement-compatibility assessment therefore uses the relevant aircraft operating condition, not merely the type name printed on the fuselage. This is one reason airport engineering departments and aircraft-performance or operations teams use formal data rather than relying on generic statements such as “this runway handles widebodies”. [3]
Does ACR greater than PCR mean the pavement will break?
No. The ACR-PCR method is a pavement-strength reporting and operating-compatibility framework, not a prediction that one excessive movement will cause immediate structural collapse. Airport pavements are fatigue structures subjected to repeated load applications. An operation above the published normal rating can consume pavement life differently from the design traffic and may require an engineering assessment. That is why the operational response is controlled permission or evaluation rather than a simplistic declaration that the aircraft physically cannot touch the pavement. [3]
Conversely, an ACR below PCR does not mean pavement condition can be ignored. Structural bearing capacity is only one dimension of pavement serviceability. Surface condition, friction, foreign-object debris, cracking, drainage, rubber contamination, snow or standing contaminants are separate operational considerations governed by other inspection, maintenance and runway-condition requirements. ACR-PCR answers the structural-strength question; it is not a complete statement of runway usability. [7]
How airports calculate and maintain the rating
FAA AC 150/5335-5D provides instructions for using FAARFIELD to calculate ACR and PCR and for reporting the resulting airport data. A technical pavement evaluation can use construction records, layer thicknesses and material properties together with pavement-condition and structural information. FAA’s separate pavement-design guidance and research programmes include methods for structural evaluation, reflecting the fact that pavement capacity changes over a long service life as traffic and condition evolve. [1] [7]
The rating therefore should not be treated as an eternal property of a runway. Pavements are maintained, rehabilitated and reconstructed; traffic mixes change; engineering data improve; and the published PCR can be updated. In the United States, the FAA AC also links PCR reporting with Airport Master Record data, and FAA implementation material required specified Part 139 public-use paved runways providing air-carrier service to have gross-weight and PCR data reported by the implementation deadline. [3]
Why the 2024 change matters to pilots and operators
The transition from ACN-PCN to ACR-PCR means older operational material can contain terminology that is no longer the current ICAO standard. ICAO’s 2026 regional implementation paper states that ACR-PCR became mandatory under the Annex 14 transition on 28 November 2024. Operators, dispatchers and aerodrome staff therefore need to recognise the newer rating and avoid treating an ACR value as numerically interchangeable with a former ACN merely because both describe aircraft pavement demand. [4]
FAA material explains one obvious numerical difference: the PCR number is one order of magnitude higher than the old PCN scale even though the five-part reporting structure remains recognisable. That makes context essential when reading historic charts or screenshots. A pavement value labelled PCN cannot simply be relabelled PCR without proper conversion or re-evaluation under the current method. Published aeronautical information and current airport data should be used. [2]
The engineering logic in one comparison
At its simplest, ACR-PCR asks whether the aircraft’s calculated pavement demand is within the pavement’s reported structural capacity for the applicable conditions. The aircraft contributes its ACR, determined from its loading and landing-gear characteristics within the ICAO model. The airport contributes its PCR, established from pavement evaluation and reported with pavement type, subgrade category, tyre-pressure category and evaluation method. If ACR is no greater than PCR and the tyre-pressure limit is respected, the published rating indicates normal structural compatibility. [2]
That simple comparison sits on top of substantial pavement engineering. It incorporates aircraft gear configuration, repeated-load effects, pavement layer behaviour and supporting ground conditions into a standardised reporting system that can be understood internationally. The value of ACR-PCR is therefore not that it replaces engineering judgement; it packages the outcome of that engineering into a common operational language. [1] [6]
Verified Sources / References
- FAA — AC 150/5335-5D, Standardized Method of Reporting Airport Pavement Strength – PCR.
- FAA — aeronautical information guidance on pavement classification codes.
- FAA — AC 150/5335-5D consolidated with January 2025 errata.
- ICAO — 2026 ACR-PCR implementation/publication status paper.
- FAA Airport Technology R&D — ICAO-ACR method and principal technical changes.
- ICAO — Airport Pavement Strength Rating training description, based on ADM Part 3.
- FAA — current airport pavement design, evaluation and maintenance advisory circulars.
Editorial Notice: This article was prepared using information considered reliable and publicly available at the time of publication. Every reasonable effort has been made to ensure accuracy; however, aviation requirements, technical standards and operational guidance may change as further information or revised regulation becomes available. This article is for general aviation education and reporting and is not a substitute for approved aircraft manuals, operator procedures, regulatory material or professional training. Cockpit King does not allege fault or responsibility against any person or organisation unless confirmed by an authoritative source. If you believe any material is inaccurate, misleading, improperly attributed or should be reviewed for amendment or removal, please contact us with the article title, the specific passage concerned and supporting evidence. We will assess legitimate requests promptly and, where appropriate, correct, clarify, update or remove the material.