As a young specialist on duty during the final descent stage on 20 July 1969 he dealt with a series of computer alarms which could have caused the mission to be aborted.

Guidance officer Steve Bales responded to the simulated error by calling an abort, which was found to be a needless reaction for that particular code.

Garman made a handwritten list of every computer alarm code that could occur along with the correct reaction to each of them and put it under the plexiglass on his desk.

[6] Bales, who as guidance officer had to quickly decide whether to abort the mission over these alarms, trusted Garman's judgment and informed flight director Kranz.

There were several additional alarms of the same type (both 1202 and also 1201, which indicated a vector accumulator area exhaustion), and then the crew was able to stop them from recurring by changing the landing procedure slightly to reduce the computer's tasks.

Bales later recalled, "Quite frankly, Jack, who had these things memorized said, 'that's okay', before I could even remember which group it was in.”[7] Garman’s quick reactions and in-depth knowledge led others on his team to give him the nickname "Gar-Flash".

[9] From 1986 through 1988 he worked at NASA Headquarters in Washington, D.C. as director of information systems services in the Space Station Program Office.