TM 1-1520-240-101-1-2 1-1-13. Aircraft Designation System.1-1-14. The designation system prescribed by AR 70-50is used in aircraft designation as follows:Example CH-47DC - Mission symbol (cargo)H - Basic mission and type symbol (Helicopter)47 - Design numberD - Series symbol1-1-15. Series and Effectivity Codes.Designator symbols listed below are used to show limitedeffectivity of airframe information material in conjunctionwith text content, paragraph titles, and illustrations. Des-ignators may be used to indicate proper effectivity, un-less the material applies to all models and configurationwithin the manual. Designator symbols precede proce-dural stepsDesignator symbols listed below are used toshow limited effectivity of airframe information material inconjunction with text content, paragraph titles, and il-lustrations. Designators may be used to indicate propereffectivity, unless the material applies to all models andconfiguration within the manual. Designator symbolsprecede procedural stepsin Chapters 5, 8 and 9. If thematerial applies to all series and configurations, no des-ignator symbol will be used.DESIGNATORAPPLICATIONSYMBOL712CH-47D aircraft equipped With T55-L-712 engines.714ACH-47D aircraft equipped with T55-GA-714A engines1-1-16. Use of “Shall, Should, and May”.Within this technical manual, the word “shall” is used toindicate a mandatory requirement. The word “should” isused to indicate a nonmandatory but preferred methodof accomplishment. The word “may” is used to indicatean acceptable method of accomplishment.1-1-17
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