Feedback from a Navy colleague and ILA SME : The Preferred Parts Selection List/Approved Parts Lists is not part of any document; it is actually developed as part of the engineering design and reliability efforts.  It typically documents the parts in the system that are critical or could cause system or mission failures, identified as part of the FMECA or other studies.    The preferred parts list from a sustainment perspective would be factored into selection of spares and spares vendors to ensure substitute parts that are functionally similar but don't meet  reliability requirements are not used.   We typically look at the Preferred parts list (or similar document) during the MS C or FRP ILA to see if there are criteria for the selection of parts/spares (and provisioning efforts) so that there is a level of confidence that the reliability will not degrade with inferior parts.  Having said that, a preferred parts list is not a mandatory or required document, it is a best practice that ensures success.   Lack of a preferred parts list does not mean the program is deficient (it could be if), it just provides a source of information of how parts will be selected.  If this is your first ILA, don't get too caught up in that - focus on if the program is meeting reliability requirements (MTBF/Ao, etc.) and if not, how will it be achieved (e.g., reliability  growth) -  and from a supply support perspective, how are parts selected and spares determined and what criteria goes into that.  The preferred parts list may come up during those discussions but don't necessarily request it up front as one of the documents you need to start the ILA.  Also, remember that the ILA criteria are tailorable, since the Handbook is written for all SYSCOMs, some of the criteria will not apply either in whole or part.  That is part of the tailoring process discussed in the handbook.  Finally,  as stated in the Handbook, the assessment criteria should NOT be used as a checklist - the criteria are top level topics that should trigger the SME to pull the string and assess the Adequacy of sustainment planning for a certain element, not necessarily a yes/no criteria to see that there is "something" in place - often that "something" does not add anything.   Hope that helps