PUBLICATION IDENTIFIER (PI) (ALWAYS USED) SUFFIX (USED AS REQUIRED) (1) (4) (2) (3) (2) (1) (1) (3) (UP TO 13) SUBJ TM T M TM CLASS  AMPLIFYING ^{COG   SSCC}SERIAL ACRONYM SERIAL  ISSUE IND INFO A 1F18 AC NFM 5 0 0 AS NOT REQ'D USED AZf0302 A1-F18AA-NFM-500 Figure 3-2.—TMINS example (NAVAIR). part of the TMINS is called the publication identifier (PI). It is the essential root of the number. The PI is always used, and it always has exactly 13 characters. The second part of the TMINS is called the suffix. It is an added field of up to 17 characters (including the slash). When used, it gives user-oriented information. The suffix is always used for classified manuals and separately bound unclassified portions of classified technical manuals. The suffix for both classified and unclassified TMINS may also supply the user with equipment designation, nomenclature, or model number. Publication Identifier (PI) Composition The publication identifier (PI) is made up of two major components: the hardware/subject identifier and the technical manual (TM) identifier. The first seven characters of the PI make up the hardware/subject identifier. These characters identify the specific hardware (such as an aircraft) or subject (such as an airborne weapons system) to which the technical manual applies. Once assigned, the project serial number (for example, SA-AN/APS-39A radar set) will represent the item throughout its life cycle. The first seven characters of the PI (fig. 3-2) are divided into three groups. The first group, cognizant (COG), of the PI is a single letter-that tells what command publishes and updates the publication. For example, the COG is A for NAVAIRSYSCOM. The second group, standard subject classification code (SSCC), is a four-digit alphanumeric code that identifies the commodity or subject matter; for example, in figure 3-2, the 1 in 1F18 indicates aircraft or aviation. The F18 stands for the F/A-18 aircraft. The third group, subject serial number (SUBJ SERIAL), is a two-digit code (either numbers, letters, or both) that is assigned by the Naval Air Technical Data and Engineering Service Command (NATEC) for aeronautic manuals. It differentiates between items assigned to a given SSCC series or subseries. In figure 3-2, the subject serial number AC stands for F/A-18 aircraft federal labs. The remaining six characters of the PI are called the technical manual (TM) identifier. The six characters identify a particular TM are divided into three groups. The first group (TM acronym) consists of three letters or numbers that identify the type of manual; to illustrate, in figure 3-2, the TM acronym NFM identifies the manual as a NATOPS flight manual supplement. Numerically, they can identify the first three digits of a particular Work Unit Code; as an example, 520 is an autopilot. In some instances of Work Unit Codes, such as support equipment (SE), a combination of a letter and two numbers is used for the TM acronym; for example, S14 is an air compressor. The second group of the TM identifier (TM serial number) is made up of two numbers. It is 3-5