ESDU 99016 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 ESDU 99015@ 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 ESDU 99015. Test data for a Boeing 727-100QC aircraft are used to illustrate@ by example@ the process of establishing a Friction Data Base. The background to the tests is described@ the method of analysis is summarised and the results are presented in tabular and graphical form. A second example@ for an aircraft where only a limited set of data is available@ is given in ESDU 99017. An example of the application of the method to ground-test machine data is given in ESDU 00018. If the method of ESDU 99015 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 to predict operational braking performance of the aircraft from day-to-day measurements from the ground-test machine.