90-24-07 MCDONNELL DOUGLAS HELICOPTER COMPANY (MDHC): Amendment 39-6784. Docket Number 90-ASW-10. Applicability: All MDHC Model 369D, 369E, and 369F/FF series helicopters certificated in any category. \n\n\tCompliance: Required as indicated, unless previously accomplished. \n\n\tTo prevent possible failure of the main rotor transmission drive assembly, which could result in loss of control of the helicopter, accomplish the following: \n\n\t(a)\tWithin the next 300 hours' time in service after the effective date of the AD or at the next annual inspection or the next time the transmission is removed, whichever occurs first, after the main rotor transmission is removed inspect the MS21250-04036 bolts which retain the debris cover, P/N 369D25174. Remove any bolts with the head inscription shown as unacceptable in Figure 1, and replace with MS21250-04038 bolts, which have a length of 2.887 plus/minus 0.010 inch. \n\n\tNOTE: MDHC Service Information Notice (SIN) DN-166.1, EN-57.1, and SINFN-45.1, dated March 14, 1990, or later revisions pertain to this subject. \n\n\t(b)\tInspect the thread protrusion of all bolts. Remove any bolt which does not protrude through the H14-4 nut for a length equivalent to two full threads (0.071 inch minimum), including the chamfer. Replace removed bolts with MS21250-04038 bolts. Torque the bolts to 50-70 inch pounds. Verify that the bolts protrude through the nut for a length equivalent to two full threads (0.071 inch minimum), including the chamfer. If more than four threads protrude through the nut, add AN960C416L or AN960C416 washers under the nut as required. Remove and reinstall parts in accordance with the manufacturer's instructions. \n\n\t(c)\tApply a white dot to the main transmission data plate to indicate that the transmission has been inspected and reworked in accordance with the manufacturer's instructions, and record compliance with this AD in the rotorcraft log book. \n\n\t(d)\tIn accordance with FAR Sections 21.197 and21.199, flight is permitted to a base where the requirements of this AD may be accomplished. \n\n\t(e)\tAn alternate method of compliance or adjustment of the compliance time which provides an equivalent level of safety, may be used when approved by the Manager, Los Angeles Aircraft Certification Office, ANM-100L, FAA, Northwest Mountain Region, 3229 East Spring Street, Long Beach, California 90806-2425. \n\n\tThis amendment (39-6784, AD 90-24-07) becomes effective on December 10, 1990. \n\n\n\n\t\t\tFigure 1. Inspection/Definition of Bolt Heads.