INTRODUCTION

This Data Item is the first of a series of examples of the application of a method for representing – and, if necessary, relating – the braking performances of aircraft and ground-test machines in wet conditions. The method, which is given in Reference 4, is essentially statistical and implies that there is a clearly-defined level of probability that can be deduced from test runs of an aircraft (or ground-test machine) in a given set of wetness conditions on a particular runway. If the runway macro-texture depth is known, then the parameter that defines the variation of effective coefficient of braking friction in the given conditions can be readily calculated from a pre-determined Friction Data Base. The concept of a Friction Data Base is explained in Reference 4.

Test data, taken from Reference 1 for a Boeing 727-100QC aircraft, are used to illustrate, by example, the process of establishing a Friction Data Base for that aircraft. The background to those tests is described in Section 3. The method of analysis is summarised and results are presented in Section 4.

A second example, for an aircraft where only a limited data set is available, is given in Reference 5. An example of the application of the method to ground-test machine data is given in Reference 6. Many other examples are considered in Reference 3.

If the method of Reference 4 is to be used to relate the braking performances of a given combination of aircraft and ground-test machine, the procedure is comprised of two distinct phases. The first is the establishment of separate Friction Data Bases for the aircraft and for the ground-test machine. The second is the prediction of operational braking performance of the aircraft using day-to-day measurements from the ground-test machine.