Within the United States and in many other countries the PCI procedure is a primary tool to evaluate the surface condition of airport pavements. The majority of the PM systems used at airports include PCI data reflecting the distresses found during visual inspection procedures. A noted short coming of many PCI based systems is that the systems tend to fix PCI values and do not really look at the distress type and it’s cause and then reflect that information in the selection of rehabilitation alternatives. As is well known, it is possible to have two pieces of pavement with the same PCI value, but drastically different distress types. One pavement having all load related distress and another having environmental distress.
With this shortcoming in mind, the AIRPORTS PCI analysis module looks at the distress type and then determines the best rehabilitation for specific distress within or on the pavement. Rehabilitation alternatives include reconstruction, structural and non-structural overlays; surface treatments and crack repair for asphalt pavements, reconstruction, overlay, slab replacement, patching and joint seal repair for PCC pavements. In the case of HKAA the system is able to use the analysis results of the PAVER system to cross check and sometimes override the structural analysis when projects or maintenance activities are recommended.

A pavement having all load related distress would then be fixed with a structural overlay, and a pavement with severe raveling and no load related damage could have a seal coat or minor overlay. This type of decision-making not only makes logical but also engineering and economic sense.

AIRPORTS needed to make maintenance programming decisions that did not conflict with other rehabilitation strategies, and provided input to the overall budgeting of maintenance and rehabilitation at the airport. A decision tree was developed to look at the PCI distress data and determine if the amount and type of distress required rehabilitation or maintenance. Maintenance projects include only those projects that the airport maintenance staff can perform including crack and joint repair and patching. The maintenance function first determines the amount of work and compares that to limits set by the user. If the volume of work falls within the maintenance work limits, then a maintenance project is selected. If not, then the system will default to a rehabilitation alternative. The PAVER trigger points for intervention are not changed.

The results of the PCI distress analysis for both maintenance and rehabilitation are output from their respective analysis modules to the main AIRPORTS module.

Roughness/Profile
Presently most airport PM systems have some idea of roughness based on the PCI distress types such as rutting, depressions, and faulting. New state of the art techniques can determine the roughness and profile information for the pavement. The large difficulty comes in integrating this valuable information into the PM system. Studies have shown that roughness has a large impact not only on the pavement life, but also on the maintenance costs for the aircraft using the pavement. AIRPORTS utilizes the roughness information to help determine the permanent deformation of the pavement. Integration of the roughness data collected at CLK is an ongoing project. Initially the system will use the data as an IRI type input to the system. At the time of writing this paper studies are going on to develop a more useful airport related standard. This new standard will be integrated to AIRPORTS upon completion.

Friction
Most large airports collect friction information to monitor rubber build-up and it’s impact on braking action under wet conditions. Decline in friction levels may also be due to aggregate polishing and loss of texture depth due to depression of the macro texture into the pavement surface as a result of loading. CLK has an on going pavement friction testing program to monitor its pavement condition. AIRPORTS integrates the friction data to the pavement modeling process such that rehabilitation may occur due to low friction values.

Structure
Structural monitoring with the Heavy Falling Weight Deflectometer, allows the engineer to calculate the stiffness of each significant layer within the pavement and its critical stresses and strains. With this knowledge it is possible to determine the mode of failure and roughly when this failure will occur with no intervention.

The Modeling
Standard deterioration models for PCI, Friction, Roughness and Structure are initially installed. These models can be models obtained from material manufactures specifications, in-situ material testing, or National or International models such as the Asphalt Institute. As information is collected and input into the systems, these models can be adjusted to the specific material laid by the contractor. If poor batches of material have been laid, the system will determine different deterioration models for these sections. The more data that is introduce into the system the more accurate are the modeling predictions. Historical data is crucial to the calibration of the system.

The second and third round of information input the system allows the PERS® system torecalibrate the prediction models for each pavement management section.

The final selection of rehabilitation options can then be more accurately determined becauseall data is considered together in deciding which treatment to choose.

User Costs
As the relationship between vertical forces on an aircraft caused by roughness is developed, more effective modeling of user costs will be available within the airport world. Presently the roughness input to AIRPORTS is "turned off". The ability to integrate user costs is built into the system, however the relationships to aircraft are still being evaluated. Future refinement of the AIRPORTS system will occur with the development of better understandings and standards of the user cost relationships for aircraft.

Delay Costs
Airports typically do not model delay costs within PM systems. However, the cost of additional taxi length, due to closure of a runway or taxiway, is significant to airlines. With the cost of jet fuel rising, the ability to model costs for construction time of each alternative and the subsequent delay costs due to the use of an alternative will enable more intelligent decision making by the airport authority. AIRPORTS allows the user the flexibility of turning this function on and off such that the input of delay costs may or may not have an influence on the decision process.

Capital Costs
The asphaltic and concrete materials on the runways, taxiways and aprons within the airport network, are one of the largest assets the airport authority controls. The AIRPORTS system allows the user to:

• Monitor the value asset over time and under different budget scenarios.
• Determine the optimum budget to sustain the asset at its current value, while giving the highest benefit to the user and the authority.

Matrix Analysis
Taking all the rehabilitation alternatives the engineer would consider, combining these with all the pavement condition information and the benefit analysis (user, delay and capital costs), allow the AIRPORTS system to create a matrix of all combination over a particular design period (0-30years). From this the system objectively chooses the most beneficial scenario to fit the user defined budget constrains.

The aim of the AIRPORTS system is not just repair the pavement once failed but time maintenance to occur when possible at a point just before pavement cracking becomes visible.

This will allow a cheaper overlay to be applied, at a time that suites the Authority, and before the integrity of the internal layers of the pavement have been compromised.

Keeping the above items in mind, the AIRPORTS system was developed to bring together all of the pertinent data with budgetary constraints and allow the user to manage his pavement.
The layout shown below reflects this integration of analysis and detail as well as the mapping link added to allow user-friendly presentation of data from the system.

This GIS linkage coupled with flexible graphing and customizable reporting functions enable easy access to all data within the system.

Additionally, keeping the international perspective in mind, the AIRPORTS system operates in any of eight languages including Chinese.