AD 85-21-51

This action publishes in the Federal Register and makes effective as to all persons an amendment adopting a new airworthiness directive (AD) which was previously made effective to all known U.S. owners and operators of certain Boeing Model 767-200 airplanes by individual telegrams. The AD requires inspection and replacement, if necessary, of self-locking nuts located in certain critical areas of the airplanes. This action was prompted by the discovery that two elevator actuator rod end bolt retaining nuts on one recently delivered Model 767 airplane did not have their intended self-locking feature. Such a nut could back off its mating bolt and result in a disconnection of the affected joint. Multiple disconnections of elevator to actuator joints could result in partial or complete loss of airplane control. These nuts have other critical applications on the Model 767 airplane, which are also addressed in the AD.

85-21-51 Boeing; Applies to Boeing Model 767-200 airplanes, certificated in any category. To prevent loss of certain critical airframe self-locking nuts, accomplish the following, unless previously accomplished:\n\n\tA. Within 35 landings or 10 days after the effective date of this AD, whichever occurs first, inspect the horizontal elevator self-locking nuts in accordance with Boeing Alert Service Bulleting 767-27A0064, dated October 25, 1985, or later FAA-approved revision. Self-locking nuts found to be insecure in accordance with the criteria specified in the service bulletin must be replaced before further flight with serviceable self-locking nuts.\n\n\tB. Within 50 landings or 20 days after the effective date of this AD, whichever occurs first, inspect the inboard aft trailing edge flap self-locking nuts and the outboard wing spoiler actuator self-locking nuts in accordance with Boeing Alert Service Bulletin 767-27A0064, dated October 25, 1985, or later FAA-approved revision.Self-locking nuts found to be insecure in accordance with the criteria specified in the service bulletin must be replaced before further flight with serviceable self-locking nuts.\n\n\tC. Alternate means of compliance which provide an acceptable level of safety may be used when approved by the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region.\n\n\tAll persons affected by this directive who have not already received the appropriate service document from the manufacturer may obtain copies upon request to Boeing Commercial Airplane Company, P. O. Box 3707, Seattle, Washington 98124. This document may also be examined at FAA Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington, or the Seattle Aircraft Certification Office, 9010 East Marginal Way South, Seattle, Washington.\n\n\tThis amendment becomes effective February 24, 1986 as to all persons, except those persons to whom it was made immediately effective by telegraphic AD T85-21-51, issued October 25, 1985.

On October 25, 1985, telegraphic AD T85-21-51 was issued and made effective immediately as to all known U.S. owners and operators of Boeing Model 767-200 series airplanes. The AD was prompted by the discovery that two elevator actuator rod end bolt retaining nuts on one Boeing Model 767 airplane, that had just been delivered, did not have their intended self-locking feature.\n\n\tSelf-locking nuts are designed to resist turning off their mating bolt by ways of friction between the nut and bolt. This feature provides additional retention capability in the event that the installation torque (clamp-up) should relax. The additional retention capability is considered essential for safe operation in certain instances. It has been determined that other nuts of the same design as those initially discovered to be discrepant do not have adequate locking friction when installed on bolts.\n\n\tThese nuts are used in the control linkages to attach the elevator hydraulic actuators to the elevator. A nonfunctioning self-locking nut could back off its mating bolt under conceivable conditions and result in a disconnection of the affected joint. Although there is redundancy in the mechanical control linkage for such disconnections, multiple disconnections could occur, or the loose actuator could damage adjacent structure. These effects could result in partial or complete loss of airplane control.\n\n\tThe same type of nut is used in the inboard trailing edge flap drive mechanism and the outboard wing spoiler control system. The consequences of a defective locknut at these locations are as critical as those described above. Therefore, corrective action is considered necessary for these applications as well.\n\n\tBoeing issued Service Bulletin 767-27A0064, dated October 25, 1985, which identifies the location of the critical suspect self-locking nuts and which specifies inspections that can be performed on the nuts to determine if there locking torqueis within an allowable tolerance. This AD makes the inspection of the nuts specified in the service bulletin mandatory, and requires the replacement, before further flight, of self-locking nuts found to be discrepant. Since it was found that immediate corrective action was required, notice and public procedure thereon were impracticable and contrary to public interest, and good cause existed to make the AD effective immediately by individual telegrams issued October 25, 1985, to all known U.S. owners and operators of certain Boeing Model 767-200 airplanes. These conditions still exist and the AD is hereby published in the Federal Register as an amendment to Sec. 39.13 of Part 39 of the Federal Aviation Regulations to make it effective as to all persons.\n\n\tThe FAA has determined that this regulation is an emergency regulation that is not considered to be major under Executive Order 12291. It is impracticable for the agency to follow the procedures of Order 12291 with respect to this rule since the rule must be issued immediately to correct an unsafe condition in aircraft. It has been further determined that this document involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034; February 26, 1979). If this action is subsequently determined to involve a significant/ major regulation, a final regulatory evaluation or analysis, as appropriate, will be prepared and placed in the regulatory docket (otherwise, an evaluation or analysis is not required).\n\nList of Subjects in 14 CFR Part 39\n\n\tAviation safety, Aircraft.\n\nAdoption of Amendment\n\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends Section 39.13 of Part 39 of the Federal Aviation Regulations as follows:\n\nPART 39--(AMENDED)\n\n\t1. The authority citation for Part 39 continues to read as follows:\n\n\tAuthority: 49 U.S.C. 1354(a) 1421 and 1423; 49 U.S.C. 106(g) (Revised Pub. L. 97-449. January 12, 1963); and 14 CFR 11.89.\n\n\t2. By adding the following new airworthiness directive: