Air Force Instruction (AFI) 11-290 requires that all operating units use proficiency data to measure the effectiveness of their cockpit/crew resource management (CRM) training programs. In response, the 512th Airlift Wing, Dover AFB and the Air Force Research Laboratory (AFRL) developed an approach whereby the Wing supplied qualified data collectors while AFRL developed process and performance instruments, "calibrated" Wing observers in the use of the instruments, and analyzed the data. Data were collected from 16 C-5 aircrews during a challenging, simulated nighttime airlift mission involving poor weather, post-takeoff landing gear malfunctions, and eventual engine failure. Building on AFRL's established methodology with the MC-130P, two expert observers independently rated CRM proficiency and mission performance using behaviorally anchored, C-5 specific scale elements. A significant correlation (r=.58) was obtained between rated overall CRM proficiency and mission performance, extending the validity of AFRL's approach to another weapon system and mission. The study also yielded a wealth of qualitative data capturing the specific CRM behaviors of successful aircrews (e.g., pilots and flight engineers directly interact to mission plan and solve in-flight problems). Data from the study were briefed to wing leaders who have already implemented the study's major recommendations as a set of training initiatives to improve the mission performance of all aircrews. The study demonstrates that, with nominal outside research support, an operational Wing can establish a valid CRM proficiency measurement program. Lessons learned from this research can be applied across major commands to ensure that all units are able to comply with the CRM proficiency data requirements of the AFI 11-290.