engineering

ACN-PCN method

ACN-PCN method is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand ACN-PCN method rather than just read about it. In short: The Aircraft Classification Number (ACN) – Pavement Classification Number (PCN) method is a standardized international airport pavement rating system promulgated by the ICAO in 1981. The method has been the official ICAO pavement rating system for pavements intended for aircraft of apron (ramp) mass greater than 5700 kg from 1981 to 2020.

Key takeaways

ACN-PCN method belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect ACN-PCN method to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of ACN-PCN method from memory before moving on to harder problems.

Reference excerpt

The Aircraft Classification Number (ACN) – Pavement Classification Number (PCN) method is a standardized international airport pavement rating system promulgated by the ICAO in 1981. The method has been the official ICAO pavement rating system for pavements intended for aircraft of apron (ramp) mass greater than 5700 kg from 1981 to 2020. The method is scheduled to be replaced by the ACR-PCR method by November 28, 2024. For the safe and efficient use of pavements, the method has been designed to:

enable aircraft operators to determine the permissible operating weights for their aircraft; assist aircraft manufacturers to ensure compatibility between airfield pavements and the aircraft under development; permit airport authorities to report on the aircraft they can accept and allow them to use any evaluation procedure of their choice to ascertain the loading the pavements can accept. The method relies on the plain comparison of two numbers:

The ACN, a number that expresses the relative effect on an airplane of a given weight on a pavement structure for a specified standard subgrade strength; The PCN, a number (and series of letters) representing the pavement bearing strength (on the same scale as ACN) of a given pavement section (runway, taxiway, apron) for unrestricted operations.

Aircraft Classification Number (ACN) The ACN calculation process is fully described in ICAO Doc 9157 Aerodrome Design Manual – Part 3 "Pavements" (2nd ed.). The procedure to calculate the ACN is as such:

Design a theoretical pavement according to a defined criterion: For flexible pavements, design the pavement for 10,000 load applications of the aircraft according to the CBR design procedure combined with Boussinesq's solution for deflection in the elastic half-space For rigid pavements, design the pavement to reach a standard flexural stress of 2.75 MPa at the bottom of the cement concrete layer according to Westergaard theory Calculate the single wheel load, inflated at 1.25 MPa, that would require the same pavement – this is the Derived Single Wheel Load (DSWL) The ACN is defined as twice the DSWL, expressed in thousands of kilograms

The ACN are calculated for four standard subgrade strengths, for flexible and rigid pavements, thus leading to 8 different values. ACNs depend on the landing gear geometry (number of wheels and wheel spacing), the landing gear load (that is dependent upon the aircraft weight and center of gravity) and the tire pressure. Normally, the aftmost center of gravity for the Maximum Ramp Weight (MRW) lead to the critical ACN. Aircraft manufacturers publish the ACNs of their aircraft in their respective Aircraft Characteristics manuals. The ICAO Aerodrome Design Manual contains the source code of computer programs for the calculation of ACNs. The FAA also developed COMFAA, a software enabling the calculation of ACNs for different aircraft depending on the input parameters.

Pavement Classification Number (PCN) Contrary to the ACN, the ICAO does not prescribe a standardized calculation procedure for the PCN. Different PCN calculation procedures may therefore be found around the world. However, the ICAO defines a standardized reporting format for the PCN that comprises the PCN numerical value and a series of 4 letters. PCN may also be known as Load Classification Number or LCN.

PCNs depend on both the pavement structure and the aircraft traffic operated on the pavement. The PCNs are determined by airports for their runways, taxiways and aprons and published in the Aeronautical Information Publication (AIP).

Application by aerodrome authorities and aircraft operators An aircraft having an ACN (at a given weight) equal to or less than the PCN can operate without restriction on the pavement, provided that its tire pressure does not exceed the PCN limitation. If the ACN exceeds the PCN, some restrictions (for example on weight of frequency of operation) may apply depending on the national or local regulations for overload operations. With the exception of massive overloading, pavements in their structural behaviour are not subject to particular limiting load above which they suddenly or catastrophically fail. As a result, minor or medium overload operations may be allowed by the airport authority depending on the corresponding loss in pavement life expectancy.

Evolutions and limitations The ACN-PCN method underwent 2 major changes since its introduction in 1981:

In 2007, the ICAO adopted a new set of alpha-factors for the calculation of ACNs on flexible pavements based on findings from full-scale pavement tests. This led to a reduction of the flexible ACNs for all landing gears with four wheels or more. In 2013, the ICAO adopted new limits for the tire pressure categories, again based on findings from full-scale pavement tests. Despite these changes, the ACN-PCN method gradually became inconsistent with recent pavement design methods, mostly based on Linear Elastic Analysis (LEA) or Finite Element Method (FEM). The method is also failing to consider accurately the effect of modern landing gear configurations (with multi-wheels arrangements) and the improved characteristics of new-generation pavement materials. As a result, the ICAO triggered the development of a new pavement rating method aimed at overcoming these deficiencies. This new system, the ACR-PCR method, became effective in July 2020.

Aircraft ACN list

References

Worked examples

Example 1 — a first encounter with ACN-PCN method

Start with the simplest possible case. Write down what ACN-PCN method claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to ACN-PCN method before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about ACN-PCN method ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of ACN-PCN method

In research: ACN-PCN method appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses ACN-PCN method in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: ACN-PCN method is common in secondary-school and first-year university syllabi. It links to neighbouring topics Airport infrastructure, Pavement engineering, so understanding it makes those chapters shorter.
In everyday life: Look for ACN-PCN method outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study ACN-PCN method in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what ACN-PCN method means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain ACN-PCN method out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is ACN-PCN method in simple terms?

Why does ACN-PCN method matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study ACN-PCN method?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on ACN-PCN method.