Why were pure turbojets ruled out for the C-101?

When defining the C-101's powerplant, the pure turbojets offered by General Electric and Rolls-Royce were soon dropped, for two reasons: cost and fuel consumption. In favor of the turbofan was an argument well known throughout the industry at the time, its efficiency and fuel savings. In CASA's trainer, the TFE731 was the favorite from an early stage of development.

The final choice fell on the Garrett engine. What weighed in its favor were the assurances the manufacturer offered regarding the fitting of its powerplant to the Aviojet, along with other factors. One of these was the company's prior experience: CASA knew the good results of Garrett engines, because the TPE-331 powered the C-212 Aviocar.

The Garrett TFE-731-2 turbofan has a high bypass ratio, 2.82:1, and a carefully designed modular construction that eases maintenance. It was originally a commercial engine that had been redeveloped for military use. Among engines in its category it offered relatively favorable performance and a high level of fuel economy.