High power applications at high speed create contact problems, increase heat sink values and transmission error (TE) during gear meshing. Hence, analyzing the gear mesh including helix angle effect, the optimization in terms of contact pressure and the transmission error reduction are all crucial for high-speed applications. In this study, meshing characteristics including helix angle based on different approaches, optimization of spur gears pairs in terms of the transmission error and contact stresses obtained from improved analytical method besides transmission design tools are all investigated for high-speed aerospace applications. Results reveal that significant transmission error reduction could be achieved by applying tip relief starting from the highest-point of single tooth contact for spur gears in aerospace applications. Hence, the need for higher contact ratio by helix angle inclusion for smoother transmission could be compensated by using tip-relief modified spur gears in gearbox since the heat sink values also need to be minimized by using relatively lower contact ratio. Results obtained from the improved analytical method by directly considering gear geometry including gear foundation effects based on direct deformation-summation approach are found in between AGMA (American Gear Manufacturers Association) standard and ISO (International Organization for Standardization) standard results.