Prepare and execute control system FAT, SAT, and commissioning plans; perform loop checks, instrument calibration verification, interlock functional testing, and regulatory control loop tuning; maintain engineering documentation including functional specifications, control narratives, I/O lists, cause-and-effect matrices, tag lists, and as-built records. Own instrument engineering scope including sizing and specification of field devices (transmitters, control valves, flow elements), instrument index and hook-up drawing development, and hazardous area classification for new and modified installations; review instrument specifications prepared by junior engineers and contractors.