Evaluation of measurement uncertainties is essential to assess measurement reliability and to be able to compare results to each other or to reference values. STAC has had two devices, of IMAG conception, for several years to measure runway friction. These devices have already demonstrated their repeatability and reproducibility. To improve the quality of STAC work, it was necessary to study and to quantify uncertainties in the field of friction measurements.
The evaluation of measurement uncertainty was conducted in accordance with the recommendations of the GUM (Guide to the expression of uncertainty in measurement). The methodology is divided into four steps:
- Analysis of measurement system
- Evaluation of standard uncertainties
- Determination of the combined uncertainty
- Calculation of the expanded uncertainty.
As no physical model is currently available, an experimental approach has been adopted for this study.
Three values of the expanded uncertainty have been obtained, corresponding to each of the test speeds. The relative weight of each factor of influence in the overall uncertainty was studied to determine the best choices and ways to improve reliability of friction results.