1-7. AUTHORITY FOR SUBSTITUTION

TM 55-1520-240-23-1 1-7. AUTHORITY FOR SUBSTITUTION Substitution or interchange of items or material for maintenance of Department of the Army aircraft shall not be authorized, nor shall orders be issued for shipment. Substitution or interchangeability shall be only by US Army Aviation and Missile Command. 1-8. CALIBRATION Within the scope of this manual there are no helicopter components, accessories, or instruments that require calibration. Special tools and test equipment shall be calibrated as specified in TB 750-25, Army Metrology and Calibration System. 1-9. EXPLANATION OF CHANGE SYMBOLS Changes, except as noted below, to the text and table and including new material on added pages, are indicated by a vertical line in the outer margin extending close to the entire area of the material affected. An exception is that pages with emergency markings, which consists of black diagonal lines around three edges, may have the vertical line or change symbol placed along the inner margins. Symbols show current pages only. A miniature pointing hand symbol is used to denote a change to an illustration. However, a vertical line in the outer margin, rather than miniature pointing hands, is used if the illustration is new, or when there have been extensive changes made. Change symbols are not used to indicate changes in the following: a. Introductory material. b. Indexes and tabular data where the changes cannot be identified. c. Blank space resulting from the deletion of text, an illustration, or a table. d. Correction of minor inaccuracies, such as spelling, punctuation, relocation of material, etc. unless such correction changes the meaning of instructive information and procedures. 1-9.1. AIRCRAFT MODIFICATION (ECP/MWO) RETROFIT INFORMATION Throughout this manual, black squares containing white numerals are used to distinguish information relating to helicopters modified by an MWO or ECP. Refer to Helicopter Configuration Legend on the following pages for specific modifications and effectivities relating to each numeral. A list of delivered helicopters serial numbers is included with the legend. Information pertaining only to unmodified helicopters is identified by the appropriate effectivity symbol preceded by WITHOUT. For example, (WITHOUT 4 ) indicates that the information that follows is applicable only to helicopters not modified by ECP D018. Information pertaining only to helicopters that have been modified by ECP D018 is preceded by (WITH 4 ). All information not preceded by an effectivity symbol is common to all helicopters. The following helicopter Designation Legend pages are solely for user convenience. They have no official status. DELIVERED HELICOPTER SERIAL NUMBERS 81-23382 through 81-23389 82-23762 through 82-23780 83-24102 through 83-24125 84-24152 through 84-24187 85-24322 through 85-24336 1-2