Aircraft low observables' features are crucial in the long-wave infrared (LW-IR) band, due to imaging sensors used in IR search and track and in the latest generation of IR-guided missiles. Earthshine irradiance on the aircraft bottom surface is an important source; hence, it is derived using data for atmospheric transmission. Emission due to skin-friction heating (important at high εbot) and earthshine reflection (important at low εbot) are compared by a dimensionless ratio for different bottom surface emissivities (εbot). The infrared cross section of aircraft in direct view from below is obtained in the LW-IR band, which shows that aircraft is seen also due to negative contrast.