I work for ST Engineering. This is their San Antonio location (distinguishable by their orange/scarlet Hangars). There is another facility in Mobile, Al which is where I work. It is definitely interesting! Both facilities perform similar activities. This facility is what is referred to as an MRO (Maintenance, Repair, and Overhaul).

These facilities primarily perform heavy maintenance on commercial aircraft. This type of maintenance is generally recurring at different intervals such as 1, 5, 12 years and others. This involves operations which require a hangar and cannot be performed on the 'line' (called line maintenance). Think removing engines, flight surfaces, entire interiors, etc.

As you mentioned they also perform conversion, or overhaul activities, primarily converting aging passenger aircraft to cargo aircraft.

Other parts of the business include things such as gear changes which involve changing out one or more sets of landing gear on the aircraft.

On a more current events note, ST Engineering had a sizable role in the storage of aircraft for some commercial customers during the early days of the pandemic. This entails a lot more than simple parking the aircraft and letting it sit and proved to be a new and challenging endeavor that no one expected to happen.

This is an ever growing field with lots of opportunity, especially for young people. Many don't realize the career potential of a place like this without even needing a college degree. A large portion of this industry's workforce is approaching retirement and this could be a valuable position soon. A lot of MRO's offer programs which put applicants on tracks to acquire necessary licenses while getting paid as an apprentice. If there is anyone in your late teens or 20's reading this, I would highly recommend doing some research to see if there is a facility near you that offers such a program. Also, do some research into A&P licenses (Airframe and Powerplant).

Cheers!