Use of AGS
There are few actual descriptions of the use of the AGS, as a landing abort was never needed during the Apollo missions. There were, however, three cases in which the AGS was used.
Its first (and intended) use was during the Apollo 10 mission, following the separation of the Lunar Module descent stage, prior to the ascent stage burn. An incorrect switch setting led to the AGS causing extensive oscillations of the ascent stage.
The next use of the AGS was during the lunar ascent phase of the Apollo 11 mission, when the LM crew performed a sequence of rendezvous maneuvers that resulted in gimbal lock; the AGS was subsequently used to acquire attitude control.
The AGS played an important role in the safe return of Apollo 13 after an oxygen tank explosion left the Service Module crippled and forced the astronauts to use the Lunar Module as a "lifeboat." Supplies of electrical power and water on the LM were limited and the Primary Guidance and Navigation System used too much water for cooling. As a result, after a major LM descent engine burn 2 hours past its closest approach to the moon to shorten the trip home, the AGS was used for most of the return, including two midcourse corrections.pp. III-17,32,35,40
Read more about this topic: Apollo Abort Guidance System