54-23-01 DOUGLAS: AD 54-23-01 as amended by amendment 39-3353. Applies to All Models DC-6, DC-6A and DC-6B Series Aircraft including military models. \n\n\tCompliance required as indicated. \n\n\tAs a result of a recent fuselage failure leading to rapid loss of cabin pressure and on the bases of information of other previous structural failures in the same locality, all fuselages in the propeller plane areas must be inspected and/or reworked as follows between stringers 23 to 26 and between Stations 217 and 280 on the left side and Stations 238 and 280 on the right side: \n\n\t1. (a) For aircraft with total service time greater than 10,000 hours the two specified areas shall be subjected to a through external inspections at each scheduled daily inspection but not to exceed 40 hours of operation. This inspection shall consist of close visual check for any evidence of skin cracks of any size or cracks in the toilet service panel pan, together with application of hand pressure at numerous points to detect any evidence of structural softness caused from stringer failures or failures of attachments of stringers to frames. For aircraft in which forward toilet has been removed, the service panel pan inspection door shall be readily openable or removable to permit the inspection of that pan. \n\n\t\t(b) If any skin cracks are evidence of structural softness is found, the airplane shall be flown unpressurized until thorough internal inspection of the area is accomplished and any failures properly repaired. \n\n\t\t(c) In any event, a thorough internal inspection of the specified areas and repair of all failures shall be accomplished within the next 2,000 hours of operations. \n\n\t\t(d) Following the first complete internal inspections and/or repairs as necessary, external inspection per item 1(a) shall be continued at intervals not to exceed 500 hours of operation, and complete internal inspection and/or rework shall be accomplished when any evidence of cracks or structural softness are found but in any event at periods not to exceed each 2,000 hours of operation. \n\n\t2. For aircraft with total time of less than 10,000 hours, the inspections of item 1(a) shall be conducted at periods not to exceed every 200 hours operations time. Action in item 1(b) shall be taken when any evidence of skin cracks or structural softness is found. \n\n\t3. When rework is made in accordance with Douglas Service Bulletin No. 602 revised September 29, 1955, for the Model DC-6, Service Bulletin No. 602 revised September 22, 1955, for the Model DC-6B and Service Bulletin No. 610 dated October 14, 1955, for the Model DC-6A; or equivalent, the inspections of items 1, 2 and 4 may be discontinued. \n\n\t4. (a) Aircraft modified for unpressurized operations by a modification approved by the Chief, Aircraft Engineering Division, FAA Western Region, and in which the initial inspections and rework, if required, have been accomplished in accordance with paragraphs 1 and 2 may:(b) At intervals not to exceed 200 hours' time in service, in lieu of the time intervals of paragraph 1 and 2, inspect the area specified by paragraph 1(a) in accordance with an FAA approved maintenance program. \n\n\t\t(c) If any skin cracks or evidence of structural softness is found, paragraph 1(c) must be accomplished. \n\n\t\t(d) Restoration of the cabin pressurization system to operational status negates the relief provided by paragraphs 4(a) and 4(b). \n\n\t5. Equivalent inspection procedures and repairs may be used when approved by the Chief, Aircraft Engineering Division, FAA Western Region. \n\n\t6. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes without differential pressure, to a base for the accomplishment of inspections required by this AD. \n\n\tThis amendment 39-3353, amending AD 54-23-01, becomes effective December 1, 1978.