FD/Chairman, Data Requirement Control PanelSeptember 27, 196868-PA-T-209APA/Chief, Apollo Data Priority CoordinationRequirement for pre-PDI IMU alignment has been deleted
After extensive Mission Techniques Panel review, it has been estab- lished that a PGNCS IMU alignment immediately prior to Powered Descent is not required for any reason. It is, in fact, undesirable at this critical time in the mission when lighting conditions couldn't be worse (local high noon!)
I also refer you to the Apollo Mission Techniques Mission G Lunar Descent Document, dated August 23, 1968 (MSC IN S-PA-8N-021), which omits this procedure – intentionally.
In order to provide documentation compatibility and accuracy, may I request you revise the Spacecraft Operational Data Book, deleting the requirement for an LM IMU alignment immediately prior to Powered Descent Initiation (PDI). For your information an alignment is performed about one hour before PDI in our current timeline.