## 2 Related Papers
The typical positioning accuracy of the aircraft from the PPP method was up to \(\pm\)0.7 m for all ENU components. On the other hand, the paper [14] presented the results of the positioning accuracy of the aircraft from the CSRS-PPP and GraftNav solutions concerning the DD differential solution. The average positioning accuracy from the PPP method was \(\pm\)0.2 \(\div\) 0.4 m; however, numerous anomalies can be observed from the GraftNav solution when the accuracy decreases to the level of \(\pm\)1.5 m. Interesting solutions for applying the PPP method for single-frequency GPS receivers were presented in papers [15; 16]. The papers described the application of the method of smoothing code measurements with GPS phase measurements using IGS (International GNSS Service) products in air navigation. The typical GPS positioning accuracy for the PPP method in works [15; 16] was about \(\pm\)1 m for all ENU and BLh frame components. Another very interesting solution for the needs of aerial photogrammetry was the application of the PPP method in the process of digital aerotriangulation in the works [17; 18]. The PPP method was used to determine the UAV position during the photogrammetric flight. The obtained PPP positioning accuracy was higher than \(\pm\)0.3 m in [17] and higher than \(\pm\)1.2 m in [19] in the ENU coordinate frame. The use of the PPP method in air navigation allowed for combining navigation solutions using different sensors, e.g., a GNSS receiver and an INS (Inertial Navigation System) system. The works [19; 20; 21; 22] presented a combined solution of aircraft positioning using the PPP/INS method in relation to the differential GPS RTK solution. The obtained PPP/INS positioning accuracy was: higher than \(\pm\)0.2 m in [19], higher than \(\pm\)0.4 m in work [20] and higher than \(\pm\)0.1 m in [21; 22]. In paper [23], the IGS and CNES (Centre National d'Etudes Spatiales) Analysis Center products were applied in aerial triangulation and, also, to determine the coordinates of an airplane. During in-flight tests in Poland, the PPP measurement technique has not been widely used as an aircraft flight reference position so far. An example of testing the vertical plane's actual flight trajectory was described in the paper [24]. In the previous flight experiments in Poland, the differential RTK technique in the OTF mode was used as the aircraft reference position. Such a solution was proposed, and in-flight tests described, among others, in research papers [25; 26; 27]. Therefore, in Polish scientific research, there is a lack of confirmation and verification of the PPP measurement method as an alternative measurement technique to determine the aircraft's real trajectory. The use of the PPP method in flight tests in Poland has been limited only to testing the precision of determining aircraft coordinates [3; 28; 29]. Moreover, in works [30; 31], the PPP method was used to determine the aircraft's precise trajectory to test the accuracy of SPP (Single-Point Positioning) code positioning in air navigation in Polish aviation. It is worth mentioning that the PPP method was used in air navigation in Poland for positioning using the GLONASS navigation system. Thus, paper [32] presented a model for determining the position of a Cessna-172 aircraft using GLONASS observations in the CSRS-PPP program. In turn, paper [33] presented the results of GLONASS positioning in the PPP method in relation to the joint GPS/GLONASS solution in the RTKLIB program. Furthermore, paper [34] presented the results of PPP positioning in GLONASS from RTKLIB and CSRS-PPP solution. The research problem of using the PPP method in air navigation, discussed in this paper, concerns both real-time positioning and post-processing mode. The presented publications [6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33] presented research works both in real-time and post-processing mode.