Superconducting electrical machines using hightemperature superconductors (HTS) are currently designed without considering losses in the non-superconducting (non-SC) substrate, silver, and copper layers of the HTS. However, alternating magnetic fields induce eddy current losses in these layers, which cannot be overlooked for certain operating temperatures and frequencies. This paper addresses these losses for a full-scale 2.5 MW aviation motor with an HTS armature winding. Using a multilayer H-A-formulated model, the magnitude of the eddy current losses are estimated and compared to the total HTS losses for frequencies between 50 and 500 Hz and temperatures between 25 and 60 K. The results show that eddy current losses are negligible for high HTS temperatures and low frequencies. However, at high frequencies and low temperatures these losses were found to represent a significant share of the total, meaning that while they can be neglected for low-speed machinery, they must be considered for power-dense machinery, particularly if the planned cooling method involves liquid hydrogen (LH2) temperatures. Finally, the work illustrates how to analyze these losses and can give designers insights related to the influence of several design variables, such as the external field, tape height, and copper purity.