83-15-51 McDONNELL DOUGLAS: Amendment 39-4789. Applies to McDonnell Douglas Model DC-9-10, -30, -40, and Military C-9 series airplanes, fuselage numbers 20 through 264, with ventral aft pressure bulkhead not in compliance with McDonnell Douglas DC-9 Alert Service Bulletin A53-144, certificated in all categories, unless already accomplished: \n\n\tA.\tFor airplanes with 30,000 or more cycles, accomplish the following within the next 100 additional cycles after the effective date of this AD: \n\n\t\t1.\tRoll back or remove and retain insulation material from aft side of bulkhead web for approximately 15 inches outboard of RH/LH edge of ventral door cutout. \n\n\t\t2.\tClean as necessary and perform close detail visual check for cracks running along AD4 rivet rows, for attaching RH/LH horizontal stiffeners, P/N 9915558, at Z=14.00, 24.00, 34.00, 48.00 and 63.50. (Reference McDonnell Douglas Service Sketch SK 3110A, Figure 1, Sheet 6.) Check for cracks for a distance of 15 inches outboard ofRH/LH edge of ventral door cutout. Removal of existing finger doublers along edges of door cutout is not required. Primary areas of interest are the outboard edges of finger doublers. \n\n\t\t3.\tIn addition to above, on Group 1 aircraft identified in McDonnell Douglas DC-9 Alert Service Bulletin A53-144, perform a visual check for cracks in the web at the upper and lower ends of the firex support stiffeners. (Refer to McDonnell Douglas Service Sketch 3109.) \n\n\tB.\tRework any cracked bulkhead panels, per McDonnell Douglas Service Sketches SK 3525 (temporary), dated July 19, 1983, or SK 3524A (permanent), dated July 18, 1983. \n\n\tC.\tSpecial flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes unpressurized to a base in order to comply with the requirements of this AD. \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, NorthwestMountain Region. \n\n\tAll persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to McDonnell Douglas Corporation, 3855 Lakewood Boulevard, Long Beach, California 90846, Attention: Director, Publications and Training, C1-750 (54-60). These documents also may be examined at the FAA, Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington, or the Los Angeles Aircraft Certification Office, 4344 Donald Douglas Drive, Long Beach, California. \n\n\tThis Amendment becomes effective January 9, 1984, and was effective earlier to those recipients of telegraphic AD T83-15-51, dated July 22, 1983.