William Murray Mack Jr., 52, chief mechanical engineer with System Planning Corp. who worked on design and installation of military radar systems, died of renal failure Aug. 11 at a hospital in Wilmington, N.C., while on vacation. He lived in Alexandria.

Dr. Mack was a former vice president for advanced projects at System Planning. He worked there on systems for the F-117 Stealth and the SR-71 Blackbird aircraft and the design of secure perimeter systems and access control for nuclear facilities and other military installations.

Dr. Mack was born in Dallas into an Air Force family. He attended Hammond High School while living in the Washington area as a teenager and graduated from the Air Force Academy High School in Colorado Springs. The family also lived in Japan.

He was a graduate of the Massachusetts Institute of Technology, where he also received a master's degree and doctorate, both in mechanical engineering. He also taught courses there that included mechanical and design engineering and heat transfer.

He worked for engineering companies in Massachusetts and Florida earlier in his career and also worked for a division of General Kinetics in Herndon. He held patents for a computerized handwriting duplication system and a device for movable walls. He taught computer courses in the Fairfax County adult education program.

Dr. Mack piloted small planes and taught flying at airports in Boston and in Florida. He was president of the Golf Course View Cluster Association in Reston and a member of three scientific or math honorary societies: Tau Beta Pi, Pi Tau Sigma and Sigma Xi. He was a volunteer usher at the Wolf Trap, Warner, Arena and Signature theaters and was honored by Warner as usher of the year in the 1997-98 season.

His marriage to Victoria Robinson ended in divorce.

Survivors include his wife, Mary Armistead Mack, and two stepdaughters, Elizabeth Anne Stief and Caroline Armistead Stief, all of Alexandria; a brother; two sisters; and a granddaughter.