GPS Ambiguity Resolution On-the-Fly (AROF) procedures process DGPS code and carrier phase mea-surements to deliver in real-time a position estimate with a centimeter accuracy in optimal conditions. They are very attractive to the civil aviation community, but ques-tions still remain unanswered about their reliability. Fol-lowing a series of papers concerning the principles of a new procedure called MAPAS, its comparison with the standard LSAST, its theoretical performances and its evaluation among three other procedures using sim-ulated data, this paper reports a preliminary evaluation of MAPAS on real measurements. The aim of this arti-cle is to estimate the performances of MAPAS from real measurements, and to emphasize problems encountered when processing real measurements with AROF proce-dures. The major data pre-processing operations applied to the raw data, such as time-matching of reference sam-ples with respect to user samples, atmospheric delays compensation and quality control of measurements, are reviewed. The main findings about MAPAS are recalled. Some results of the application of MAPAS to real mea-surements collected using a NOIWEL GPS signal gen-erator and from real life field measurements are pre-sented. The influence of the data pre-processing meth-ods is stressed. A preliminary evaluation of the integrity and of the availability of the precise position delivered by the procedure is presented.