AD 96-03-02

Effective February 16, 1996.

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of February 16, 1996.

Comments for inclusion in the Rules Docket must be received on or before April 1, 1996.

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-103, Attention: Rules Docket No. 96-NM-02-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

The service information referenced in this AD may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

James G. Rehrl, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2783; fax (206) 227-1181.

The FAA recently received a report of the collapse of the right main landing gear (MLG) of a Boeing Model 767-300ER airplane while the airplane was taxiing in a low speed right-hand turn. Investigation revealed that the cause of the collapse of the MLG was attributed to the fracture of the aft trunnion outer cylinder due to stress corrosion cracking. The cracking initiated at the crossbolt hole, which is approximately five inches from the aft trunnion bushing flange. This condition, if not corrected, could result in the collapse of the MLG due to ductile fracture of the aft trunnion of the outer cylinder.

The FAA has reviewed and approved Boeing Alert Service Bulletin 767-32A0151, dated November 30, 1995. The alert service bulletin places affected airplanes into three categories:

Category 1 airplanes have outer cylinders of the MLG that have accumulated 2\1/2\ years or less since the cylinder was new or overhauled.

Category 2 airplanes have outer cylinders of the MLG that have accumulated between 2\1/2\ years and 4 years since new or overhauled.

Category 3 airplanes have outer cylinders of the MLG that have accumulated 4 years or more since new or overhauled.

This categorization reflects the time-related phenomenon of corrosion; i.e., the risk of developing corrosion (or stress corrosion cracking) increases with the length of time that an outer cylinder has been in service. Therefore, Category 3 comprises airplanes that are generally at the greatest risk of experiencing stress corrosion cracking .

The alert service bulletin describes the procedures necessary for performing various visual, eddy current, and ultrasonic inspections; and when appropriate, for performing chemical spot testing of the aft trunnion of the outer cylinder of the MLG (hereinafter referred to as the ``aft trunnion''). It also includes the following actions for all three categories of airplanes:

1. replacement of the outer cylinder, if cracking is found;

2. replacement of the aft trunnion bushing and crossbolt bushings; or repeat the visual, eddy current, and ultrasonic inspections of the immediate area in which corrosion is found in the aft trunnion;

3. application of plating and finish to the outer cylinder, if the finish is found to be damaged or missing;

4. functional testing of the lock link actuator;

5. repetitive visual inspections, or termination of the inspections by repairing the outer cylinder and installing flangeless aft trunnion bushings and new crossbolt bushings;

6. repetitive 360-degree close visual inspection of the aft trunnion, including the crossbolt area;

7. application of corrosion inhibiting compound on the aft trunnion; and

8. eventual repair of the outer cylinder and replacement of the existing aft trunnion and crossbolt bushings with new bushings, which terminates the inspections specified in the alert service bulletin.

The alert service bulletin refers to Boeing Alert Service Bulletin 767-32A0148, dated December 21, 1995, which describes procedures for repair of the outer cylinder and replacement of the existing bushings of the aft trunnion and crossbolt of the MLG with new bushings. The FAA has also reviewed and approved this alert service bulletin.

Since an unsafe condition has been identified that is likely to exist or develop on other Model 767 series airplanes of the same type design, this AD is being issued to prevent the collapse of the MLG due to stress corrosion cracking of the aft trunnion of the outer cylinder. This AD requires various inspections to detect cracking and corrosion of the aft trunnion and various follow-on actions. The actions are required to be accomplished in accordance with Boeing Alert Service Bulletin 767-32A0151, described previously.

The compliance times for accomplishing these inspections are dependent upon the age of the outer cylinders of the MLG. Category 3 airplanes, which have the oldest cylinders, are to be inspected within 30 days (the alert service bulletin recommends inspecting these airplanes within 60 days). Category 2 airplanes are to be inspected within 90 days (the alert service bulletin recommends inspecting these airplanes within 120 days). Category 1 airplanes, which have the youngest cylinders, are to be inspected within 150 days (the alert service bulletin recommends inspecting these airplanes within 180 days).

In developing an appropriate compliance time for this action, the FAA considered not only the degree of urgency associated with addressing the subject unsafe condition, but the manufacturer's recommendation as to an appropriate compliance time, the availability of required parts, and the practical aspects of performing the inspections. The FAA points out that the varying compliance times allow the manufacturer sufficient time to produce all the eddy current probes, ultrasonic transducers, and non-destructive inspection (NDI) reference standards that operators need to accomplish the inspections. Further, the FAA took into account the compliance times recommended by the manufacturer, as well as the number of days required for the rulemaking process; in consideration of these factors, the FAA finds that the compliance times required by this AD will fall approximately at the same time as those recommended by the manufacturer.

Operators should note that, although Boeing Alert Service Bulletin 767-32A0151 specifies eventual repair of the outer cylinder and replacement of the existing bushings with new bushings, this AD does not require such replacement. The FAA is considering further rulemaking action to require eventual replacement of the bushings. However, the planned compliance time for the replacement is sufficiently long so that prior notice and time for public comment will be practicable.

This AD does provide operators with the option of terminating the requirement for the repetitive inspections by replacing the bushings with new bushings in accordance with Boeing Alert Service Bulletin 767-32A0148, dated December 21, 1995. Accomplishment of this bushing replacement also terminates the requirements of the following AD's:

AD 95-19-10, amendment 39-9372 (60 FR 47689, September 14, 1995), and

AD 95-20-51, amendment 39-9398 (60 FR 53109, October 12, 1995). [The comment period for AD 95-20-51 was extended by an AD action that was issued on November 28, 1995 (60 FR 62321, December 6, 1995.)]

Operators should also note that Boeing Alert Service Bulletin 767-32A0148 refers to Component Maintenance Manual (CMM) 32-11-40, which, in turn, provides instructions for plugging the aft trunnion lubrication fitting with a rivet. This AD, however, does not require plugging this lube fitting to terminate the requirements of this AD, AD 95-19-10, or AD 95-20-51.

Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption ADDRESSES. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket Number 96-NM-02-AD.'' The postcard will be date stamped and returned to the commenter.

The regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a ``significant regulatory action'' under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption ADDRESSES.

Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

1. The authority citation for part 39 continues to read as follows:

Authority: 49 USC 106(g), 40113, 44701.