Problem of Coplanarity of Energy Flows in EAS Cores

The effect of the trend that, according to observations in high-altitude and stratospheric experiments with x-ray emulsion chambers, the most energetic particles and/or groups of particles in gamma–hadron families show toward coplanar arrival is discussed. Experimental data are compared with the results of calculations performed within various versions of the FANSY 2.0 model, which include a version that reproduces coplanar generation of the most energetic particles in hadron interactions at ultrahigh energies. The whole body of experimental data on azimuthal characteristics of gamma–hadron families observed at the levels of 25, 75, and 600 g/cm $${}^{2}$$ in the atmosphere is not explained even within the FANSY 2.0/2D model, which employs the hypothesis of connection between coplanarity and a local 3D $${\leftrightarrow}$$ 2D evolution of the signature of metric at ultrahigh energies.