83-20-04 McDONNELL DOUGLAS: Amendment 39-4740. Applies to McDonnell Douglas Model DC-6, -6A, -6B, R6D (Navy), and C118 (USAF) series airplanes, certificated in all categories. \n\n\tCompliance required as indicated, unless previously accomplished. \n\n\tTo detect cracks and prevent failure of the horizontal stabilizer rear spar caps accomplish the following: \n\n\tA.\tWithin the next 30 days after the effective date of this AD, unless already accomplished, inspect and repair, if necessary, the horizontal stabilizer upper and lower rear spar cap attach fittings on both sides of station 63 in accordance with the Accomplishment Instructions of McDonnell Douglas Service Rework Drawing J060265 "N/C" dated July 29, 1983, hereinafter referred to as Rework Drawing, or later revisions approved by the Manager, Los Angeles Aircraft Certification Office, FAA, Northwest Mountain Region, as follows: \n\n\t\t1.\tIf no cracks are found in the rear spar attach fittings, apply primer and lacquer top coat(lacquer top coat optional). Apply LPS-3 corrosion inhibiting oil, or equivalent when approved by the Manager, Los Angeles Aircraft Certification Office, FAA, Northwest Mountain Region, throughout the attach fitting (bathtub area) and reinstall the bolt per the Rework Drawing. Conduct repetitive inspections per the Rework Drawing at intervals not to exceed 12 calendar months. \n\n\t\t2.\tIf a crack is found equal to or exceeding 1/2" at location A, 3" at location B, or 6" at location C as defined in figure 2 of the Rework Drawing, accomplish the repair in (a) or (b) below, prior to further flight: \n\n\t\t\t(a)\tIf the crack is inboard of station 63, repair in accordance with the Accomplishment Instructions of the Rework Drawing. \n\n\t\t\t(b)\tIf the crack is outboard of station 63, repair per the McDonnell Douglas DC-6 Structural Repair Manual, Tail Group, Page 138, Figure 134, dated October 15, 1952. \n\n\t\t3.\tIf a crack is found that is less than 1/2" at location A, 3" at location B, or 6" at location C, repetitively inspect per the Rework Drawing at intervals not to exceed: \n\n\t\t\t(a)\tfor location A: 7 calendar days, or prior to further flight, whichever occurs later. \n\n\t\t\t(b)\tfor location B: 14 calendar days, or prior to further flight, whichever occurs later. \n\n\t\t\t(c)\tfor location C: 21 calendar days, or prior to further flight, whichever occurs later. \n\n\tB.\tRepairs per Paragraph 2, above, constitutes terminating action for the repetitive inspections required by this AD only at those locations repaired. \n\n\tC.\tIf more than one crack is found, repair all cracked areas as specified in Paragraphs A. 2(a) and/or 2(b), above. \n\n\tD.\tAlternate means of compliance which provide an equivalent level of safety may be used when approved by the Manager, Los Angeles Aircraft Certification Office, FAA, Northwest Mountain Region. \n\n\tE.\tSpecial flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base to comply with the repair requirements of this AD when approved by the Manager, Los Angeles Aircraft Certification Office, FAA, Northwest Mountain Region. \n\n\tThis Amendment becomes effective October 19, 1983.