75-20-02 BOEING: Amendment 39-2369 as amended by Amendment 39-2501. Applies to Model 737 series airplanes, Line Nos. 1 through 299 inclusive, certificated in all categories. Compliance required as indicated unless already accomplished. \n\tTo prevent unwanted trailing edge flaps retraction and leading edge flap extension, accomplish the following: \n\tA.\tAirplane Line Nos. 1 through 269 with flap power unit assemblies not modified in accordance with Boeing Service Bulletin 737-27-1041, Revision 4, Part II, or later FAA approved revisions, within the next 750 landings, unless accomplished within the last 250 landings, and at times thereafter not to exceed 1,000 landings, inspect the flap power unit in accordance with paragraph C. \n\tB.\tAirplane Line Nos. 270 through 299, or those earlier aircraft with flap power unit assemblies modified per Boeing Service Bulletin 737-27-1041, Revision 4, Part II, or later FAA approved revisions, within the next 750 landings, unless inspected within the last 750 landings, inspect in accordance with paragraph D.\n \tC.\tInspect the worm teeth in the flap power unit for wear in accordance with Boeing Service Bulletin 737-27-1041, Revision 4, or later FAA approved revisions, or in a manner approved by the Chief, Engineering and Manufacturing Branch, FAA Northwest Region. Flap power unit assemblies with worm teeth worn beyond the limits prescribed in the service bulletin, must be modified prior to further flight in accordance with Boeing Service Bulletin 737-27-1041, Revision 4, Part II, or later FAA approved revisions, or in a manner approved by the Chief, Engineering and Manufacturing Branch, FAA Northwest Region. Repetitive inspections for modified units are to be made in accordance with paragraph E. \n\tD.\t1. Inspect the worm gear for wear in accordance with either inspection procedure in Boeing Service Bulletin 737-27-1076, Revision I, Part III, or later FAA approved revisions, or in a manner approved by the Chief, Engineering and Manufacturing Branch, FAA Northwest Region. Repetitive inspections are to be accomplished at intervals specified in either Method I or Method II of paragraph B, Part III, of the service bulletin, but not to exceed 5,000 landings for Method I or 3,000 landings for Method II. \n\t\t2.\tFlap power unit assemblies with worm gears worn beyond the limits specified in the service bulletin are to be replaced with new parts prior to further flight. \n\tE.\tFlap power units repaired in accordance with paragraph C or D2 must be inspected during 1400-1600 landings after new parts are installed, in accordance with paragraph D1 above, and thereafter comply with paragraph D. \n\tF.\tThe inspections required by this directive may be terminated when the mechanical trailing edge flap asymmetry system has been replaced with the electrical system in accordance with Boeing Service Bulletin No. 737-27-1079 and; \n\t\t1.\tA new worm gear has been installed in the trailing edge flap drive power unit in accordance withBoeing Service Bulletin No. 737-27-1076, or the existing worm gear has been inspected in accordance with Service Bulletin No. 737-27-1076 and no perceptible wear groove can be identified on the side of any tooth, or other modifications approved by the Chief, Engineering and Manufacturing Branch, FAA Northwest Region are made and, \n\t\t2.\ta new worm has been installed in the trailing edge flap power drive unit in accordance with Boeing Service Bulletin No. 737-27-1041 Revision 4, or the existing worm has been inspected in accordance with Service Bulletin No. 737-27-1041 Revision 4 and no perceptible wear groove can be identified in the side of any tooth, or other modifications approved by Chief, Engineering and Manufacturing Branch, FAA Northwest Region are made. \n\tG.\tUpon request by an operator, through an appropriate FAA maintenance inspector, subject to approval by the Chief, Engineering and Manufacturing Branch, FAA Northwest Region, the repetitive inspection period herein may be adjusted for that operator if the request contains adequate substantiating data to justify the increase. \n\tH.\tFor the purposes of complying with this AD, subject to acceptance by the assigned FAA maintenance inspector, the number of landings on the flap power unit worm gear may be determined by actual count or by dividing each airplane's hours time in service since the flap power drive unit was installed, by the operator's fleet average time from takeoff to landing for the airplane type. \n\tThe manufacturer's specifications and procedures identified and described in this directive are incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1).\n \tAll persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to Boeing Commercial Airplane Company, P.O. Box 3707, Seattle, Washington 98124. The documents may also be examined at FAA Northwest Region, 9010 East Marginal Way South, Seattle, Washington.Amendment 39-2369 became effective October 27, 1975. \n\tThis Amendment 39-2501 becomes effective February 9, 1976.