What is the ruling of the Sharia on a girl joining an aviation school that stipulates the removal of the khimar and the wearing of a cap that covers the hair, along with the modest official uniform?

A hat is not considered a legitimate Islamic head covering (hijab) because it does not achieve the required concealment, and it does not cover the chest. The uniform for studying this field often does not meet Islamic legal conditions, so it is not permissible for a woman to enroll in it. Furthermore, studying and working in this profession entails other Islamic legal prohibitions, such as mixing with men, traveling without a mahram, and being in seclusion.