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The International Runway Friction Index (IRFI)-Ready for the Real World?
by Angelo Boccanfuso, Senior Development Officer (R&D), Transportation Development Centre, Transport Canada

This article was originally published in International Airport Review (IAR), Volume 9, Issue 1/2005, reprinted with permission.

The development of an IRFI is a testament to international cooperation within the aviation industry. With most technical milestones passed, Angelo Boccanfuso reports from the latest International Meeting on Aircraft Performance on Contaminated Runways (IMAPCR) that further consensus on practical implementation and funding are now needed...

Not only is there no common indicator of contaminated runway conditions in use worldwide, but winter procedures vary from airport to airport, and from country to country. After winter testing spanning a period of eight years, the Joint Winter Runway Friction Measurement Program (JWRFMP), a cooperative international initiative coordinated by Transport Canada, has reached a major turning point in the decades-old search for a way to measure runway friction and present the data to pilots in a useful way.

IMAPCR 2004

This article presents the results of the third IMAPCR, held in Montreal in November 2004. What emerged from this meeting, which is held every four years, was general agreement that the science behind the concept of an IRFI is workable. However, further work may be needed to turn the results of the research into a practical and useful tool for all of the stakeholders.

Organized by Transport Canada, in partnership with the National Aeronautics and Space Administration (NASA) and the Federal Aviation Administration (FAA), and held at the International Civil Aviation Organization (ICAO) headquarters, IMAPCR drew a wide variety of participants with a professional interest in aircraft operations in severe winter conditions, and focussed on the JWRFMP's findings. JWRFMP has assembled a database with the results of over 10 000 ground runs with more than 12 different types of friction testers and 8 different aircraft. It has produced what it believes are the necessary building blocks for an IRFI.

That success is a tribute to the extraordinary level of international cooperation that assembled a group of professionals and organizations-pooling facilities and resources to enable a major research program at a relatively low cost.

At the moment, airport operators and pilots rely on a system that lacks a common standard and utilizes varying devices and differing terminology. The JWRFMP has greatly improved the safety of the system simply through disseminating information and increasing operator awareness. The meeting heard repeated calls for an international measuring and reporting system. It is not enough for each country to adopt its own measuring and reporting system and assume the job has been completed.

Working with an index

For an IRFI to work though, it requires, first of all, a common reference for the various ground vehicles used at various airports-an international reference vehicle (IRV). The IRV used in the research program was a French-designed instrument de mesure automatique de glissance (IMAG). Friction values of other devices were harmonized with those of the reference vehicle through linear regressions.


IRV used in the research program was this French-designed instrument de mesure automatique de glissance (IMAG)

Although the IRFI concept is simple, the logistics of implementing it are more complex. Any system needs to take into account the responsibility of the airport against that of the airline or pilot, and the balance between commercial pressures and safety. Any additional cost incurred by IRFI might be offset in the long run if airports or airlines could reduce conservative safety margins resulting from unreliable equipment or subjective procedures.

A key question raised during IMAPCR was whether it is necessary, or even possible, to regulate an IRFI. It is difficult to regulate a concept, but once the concept is embraced, there are aspects that can be regulated or better controlled. For example, performance criteria for friction measuring vehicles, the winter conditions in which they operate, the manner in which measurements are reported, the expiry times for condition reports and the legal implications. These are manageable in the short term and can offer immediate safety benefits.

Information for airport operators, which enables them to make best decisions about their runway friction measuring equipment requirements, for the accuracy, quality, and reproducibility they should expect, is currently unavailable. There are few local, and no international, mechanisms or bodies that monitor friction equipment and performance. Some friction testers have been on the market for years without development and there is no process for acceptance. The issue of an approval process will need to be addressed if the aviation community adopts the IRFI concept.

Various outstanding items were identified for further work:

  • JWRFMP's extensive research data should be summarized, including the results and conclusions of more than 40 research reports and the proceedings of IMAPCR 2004.
  • The harmonization and calibration of devices (master and local) need to be further refined against the IRFI standard device.
  • A final decision is needed on the IRFI reference vehicle-IMAG, electronic recording decelerometer (ERD), or some other device. This will allow discrepancies between devices to be addressed and will also be beneficial for runway maintenance. Selecting the IRV means taking into account the congested airport environment typically found in Europe. It should also be able to take accurate readings on wet runways.
  • The bulk of the data demonstrates that the ERD has the best correlation to aircraft braking coefficient (mu) on ice and compacted snow surfaces. Tests should be reviewed so that if IRFI is used as an international standard, procedures can be developed to establish a better correlation between an aircraft mu and IRFI.

Correlation with aircraft braking performance

The key objective of the research has been to demonstrate that a correlation between ground friction measurements and aircraft braking performance exists. This was clearly shown at IMAPCR-not only in theory but in practical application as well. Although some aircraft manufacturers have maintained that an aircraft's braking coefficient cannot be related to ground friction measurements, the results presented at IMAPCR seemed to demonstrate otherwise. As a result, the European Aviation Safety Agency (EASA) is considering amendments to their certification specifications for large aeroplane operation on contaminated runways to reflect these findings.

One of the most concrete developments to come out of the JWRFMP work is the Canadian Runway Friction Index (CRFI), which shows good correlation between friction values measured by the ERD and aircraft braking performance. This is due to the consistency between surface friction, as defined by surface condition and the deceleration of both the aircraft and the ERD.

But while the research has shown that IRFI can be used to predict aircraft braking performance, data analysis suggests that converting CRFI to IRFI using harmonization constants may not be the solution, because the correlation to aircraft mu may be less reliable on certain winter surfaces.

Work is ongoing to determine whether IRFI readings can be used in the CRFI tables. If readings for similar surface contamination are not equivalent, IRFI landing tables could result in serious underestimation of aircraft landing distances under certain conditions.

As participants at IMAPCR 2004 pointed out, any system such as CRFI can have limitations. For example, it is dependent on the accuracy and timeliness of runway friction reporting. The CRFI is not aircraft-specific, which means that built-in safety margins may be too conservative for some aircraft. However, CRFI is built on actual flight test data, and currently provides advisory material where no other information may exist. For this reason, Transport Canada intends to propose the CRFI to ICAO as a recommended practice.

The need for the IRFI

The financial consequences of closing a runway can be significant to both the airport and the air operator. The question of legal liability for the consequences of any decision is a major one. Faced with a poor friction report, should the airport be obliged to take action, or should they simply be required to relay friction data, leaving the final decision whether to land in the hands of the pilot?

Some European airports, such as Munich International Airport have seen an increase in runway closures since deciding to impose their own operational limitations. However, Henning Pfisterer, Manager of Airport Safety at Munich, told IMAPCR that pilots would not have opted to land in 90 percent of closures, so the actual loss of runway time was insignificant. Mr. Pfisterer said the airport considers that taking the risk for the remaining 10 percent of cases to be a good business decision.

Airports globally are looking to ICAO to establish clearly-defined operational limitations on contaminated runways. Individual policies, such as those at the Munich airport, can only be considered an interim solution. Airport operators at IMAPCR clearly stated that international standards would not only make a contribution to flight safety, but also provide a reliable legal framework for the industry. They were also of the opinion that the most important goal is to get the best information possible to pilots.

What's missing?

For airlines, there are procedural questions. Air Canada, for example, believes that fundamental problems with measurement timeliness and weather forecasting limit the relevance of runway condition measures at the time of flight dispatch. However, the airline considers near real-time friction reporting to be an achievable, significant safety improvement, and encourages further development. In relation to this, by utilizing the results from the JWRFMP, and synchronizing friction data with observations of contaminant type, Finnair has developed a decision-making tool that enables a pilot to perform calculations using the latest reported information.

There was a consensus at the meeting that friction reporting and measuring may be most useful for integrating into tactical decision-making tools and the provision of expiry times to ensure that obsolete data is not passed on to pilots. Airlines, such as Finnair, have demonstrated that a system can be implemented that results in improved safety and a decision-making tool, without imposing an additional regulatory burden. The question of legal liability in overriding manufacturer data was also raised as an issue. It was discussed that the CRFI sometimes permits landing when aircraft manufacturer guidelines recommend against it. Most are opposed to overriding manufacturer-provided landing information.

Furthermore, pilots present at the meeting stated that the most important consideration in using the work done by JWRFMP is ease of use. Captain Dennis Landry of Northwest Airlines, who is also Chairman of Special Projects for the Air Line Pilots Association (ALPA), told IMAPCR that those who develop the system must recognize that pilots need a simple solution. He stated that the CRFI system, although not officially adopted by the airline, is provided to the pilots and forms part of their general pilot education.

Kevin Hollands, Chief Pilot at Canada's WestJet Airlines, said the key consideration is how to apply techniques to strategic and tactical decision making regarding the safety of a runway. He said CRFI works because it has been accepted by pilots, uses standard techniques, and acts as a component of a system that can be used with standard aircraft movement surface condition reports.

Overall, the pilots agreed that a procedure is needed to link strategic and tactical decision-making tools regarding the suitability of a runway for landing. Manufacturers' data may be based on conservative estimates for surfaces such as ice, and therefore may not be used consistently.

The impact on aircraft manufacturers

While aircraft manufacturers provide operators with data to address contaminated runways, they do not provide any correlation of aircraft braking coefficients with runway friction. Since there is no common friction index for all devices, it is up to individual operators or authorities to relate the aircraft braking coefficients or wheel braking coefficients with a generic or airport-specific friction device.

Representatives from one major manufacturer told IMAPCR that while an IRFI appears capable of providing a more consistent way to assess runway friction for runway condition reporting, more work needs to be done to establish the correlation between the IRFI and aircraft braking. In particular, Boeing is concerned that the conservative assessments of braking required when using ground vehicle data may result in weight penalties that may not be necessary. It will be important to find a balance between the safety margin required and what an operator can accept.

Improving devices

It became evident at IMAPCR that manufacturers also need regulations and rules with some kind of independent review. There are currently no performance criteria that a manufacturer must meet. At the same time, some noted that introducing regulation into an unregulated industry will mean confronting issues such as competition between firms, vested interests, balancing commercial interests with client needs, standards that may raise costs, and even the possibility that some equipment may not meet regulations at all.

Frank Holt, Vice-President of Friction and Pavements at Dynatest International A/S, pointed out that the IRFI offers the advantages of acceptance; conformity of equipment, data and calculations; improved safety; and the elimination of substandard equipment and procedures. He said that an IRFI is possible, but authorities must take the lead and mandate it.

Participants generally agreed that adopting and putting into practice an international runway friction reporting system on an international scale requires the support and commitment of the international aviation community.

Conclusion

The interest and discussion generated at IMAPCR 2004 showed that measuring and reporting friction and relating it to aircraft landing distance remains an active concern. It was encouraging to see how different operators use data generated by the research program and apply it to their own operations.

A standard to calculate the IRFI has been developed by the American Society for Testing and Materials (ASTM) that accommodates all major measurement techniques and equipment currently used around the world. ASTM standards are in development for specifications for an IRV for IRFI, for the design and construction of an IRV, for a standard practice guide for friction measurements of aerodrome runways (WK5710), and for a standard practice guide for calculating an aircraft friction index (WK5711).

While development of a standard is an important step, it must be followed by implementation. Calibration of local measuring devices, for example, is critical. Once the final selection of the IRV has been made, a process for calibrating individual devices needs to be put in place. While the establishment of testing centres may offer a solution, it remains to be determined whether harmonization constants remain stable or whether individual devices would have to be retested or calibrated every year. There is some research that suggests that every three years would be sufficient. Manufacturers at IMAPCR raised concerns about who would bear the costs of calibration.

Many at IMAPCR 2004 agreed that an important next step is an independent assessment of whether in fact an international methodology can be developed. Several countries, including Canada, have proceeded to implement their own systems, which, while improving domestic safety, do not address the issue on an international level. Many participants suggested that ICAO should establish a working group to deal with the questions of standardization and new industry practices.

The general consensus at IMAPCR 2004 was that the aviation community needs to act on the current research findings. What is not clear is who will bear the cost.

Proceedings from IMAPCR 2004 were published on CD in the spring of 2005. For information on ordering, visit the Transportation Development Centre Web site at www.tc.gc.ca/tdc/menu.htm.

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