## 1 Introduction
However, the combination of sophisticated modern airport pavement design methods, with the simpler methods embedded in ACN-PCN for pavement strength rating, has resulted in anomalies. The most common example is where a pavement is appropriately designed for a fleet of aircraft, but when the design is complete and the strength rating is assigned, the simpler mathematics associated with ACN-PCN results in a strength rating that does not allow all the aircraft in that fleet to operate in an unrestricted manner. For example, a B777-300 ER has an ACN of 121 on a flexible pavement with a subgrade category D. When a pavement is designed using the layered elastic software FAAFRIELD [8] but is rated by the software COMFAA [13] according to the FAA method, it is possible that a PCN of 118 is assigned, and an unintended operational restriction is triggered. In theory, that requires a pavement concession for the B777-300 ER, even though it was appropriately provided for in the pavement thickness design. The most concerning example of these potential anomalies occurred in new airport developments in India, where private entities were contracted to construct new airports to cater to certain numbers and types of aircraft, with all pavements designed and constructed according to the requirements of the FAA. When the construction was complete and the pavement strength rating was performed for the airport authority, the anomalies had the potential to cause some runways to need to provide a pavement concession for the most damaging aircraft in the design aircraft fleet [14]. This could have been interpreted to mean that the private contractor had failed to deliver on the project requirements, and this could have resulted in contractual disagreement. In reality, the contractor would have designed and constructed the pavements as required, but differences between pavement design and pavement strength rating potentially resulted in some runways being rated slightly below that required to allow all the aircraft in the design traffic fleet to operate in an unrestricted manner. [PERSON] and [PERSON] [14] subsequently recommended that future pavement strength ratings be performed in FAARFIELD, taking advantage of the more sophisticated mathematics already being used for pavement thickness design. In response to these anomalies between pavement thickness design and pavement strength rating, ICAO developed a new strength rating system that uses more sophisticated mathematics aligned to those used in modern pavement thickness determination software [15]. The new system, known as Aircraft Classification Rating-Pavement Classification Rating, or ACR-PCR [16], operates in a similar manner to ACN-PCN [17]. However, every aircraft has a new ACR value that cannot be uniquely scaled from the equivalent ACN. As a result, each airport must determine and publish a new PCR to replace the current PCN for each of their runways, and this is due to be implemented by November 2024 [18]. The aim of this research was to review the new international airport pavement strength rating system, known as ACR-PCR. Potential improvements to the system are then explored to address any issues or missed opportunities. It is hoped that the identified issues and potential improvements will increase the usefulness of the new system and reduce the burden associated with the transition from the existing system to the new one.