Discussion
The Luftfahrt-Bundesamt (LBA), which is the airworthiness authority for Germany, recently notified the FAA that an unsafe condition may exist on certain Stemme Models S10, S10-V, and S10-VT sailplanes. The LBA reports that cracks were found on the flight control longitudinal coupling during a static load test on the elevator control system.
The cracks were such that the flight control system would have most likely failed in a short period of operating time with reduced or loss of control of the sailplane.
Other parts in the flight control system have the same type of force intersection design and cracks could exist or develop in these areas also. These areas are the wing flap coupling, part number (P/N) 10SW-RVW; the airbrake control coupling, P/N 10SB-RVW; the flap drive rocker, P/N 10SW-RMW; and the flap/aileron interference shaft, P/N 10SQ-RMW.
Cracks in any of these areas, if not detected and corrected in a timely manner, could result in flight control system failure with consequent reduced or loss of control of the sailplane.
Relevant Service Information
Stemme has issued Service Bulletin A31-10-032, Amendment-Index 02.a, dated July 10, 1998, which specifies procedures for inspecting the following parts for cracks:
- The flight control longitudinal coupling, part number (P/N) 10SH-RVH;
- The wing flap coupling, P/N 10SW-RVW;
- The airbrake control coupling, P/N 10SB-RVW;
- The flap drive rocker, P/N 10SW-RMW; and
- The flap/aileron interference shaft, P/N 10SQ-RMW.
This service bulletin also references Stemme Installation Instructions A34-10-032-E, Amendment-Index 01.a, dated August 10, 1998, which includes procedures for replacing the flight control longitudinal coupling, with modified P/N 10SH-RVH coupling.
The LBA classified this service information as mandatory and issued German AD 1998-323, dated July 1, 1998, in order to assure the continued airworthiness of these sailplanesin Germany.
The FAA's Determination
These sailplane models are manufactured in Germany and are type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the LBA has kept the FAA informed of the situation described above.
The FAA has examined the findings of the LBA; reviewed all available information, including the service information referenced above; and determined that AD action is necessary for products of this type design that are certificated for operation in the United States.
Explanation of the Provisions of This AD
Since an unsafe condition has been identified that is likely to exist or develop in other Stemme Models S10, S10-V, and S10-VT sailplanes of the same type design registered for operation in the United States, the FAA is taking AD action. This AD requires inspecting the areas of the flight control system previously referenced for cracks; immediately replacing any cracked parts; and eventually replacing all longitudinal coupling with modified coupling regardless if found cracked.
Accomplishment of the inspection will be required in accordance with Stemme Service Bulletin A31-10-032, Amendment-Index 02.a, dated July 10, 1998.
Accomplishment of the longitudinal coupling replacement will be required in accordance with Stemme Installation Instructions A34-10-032-E, Amendment-Index 01.a, dated August 10, 1998.
Accomplishment of the replacement of any other cracked part in the flight control system will be required in accordance with procedures obtained from the manufacturer through the FAA, Small Airplane Directorate.
Possible Follow-up Action
Stemme has modified the longitudinal coupling, but has not modified the wing flap coupling, the airbrake control coupling, the flap drive rocker, and the flap/aileron interference shaft. If cracks are found on parts other than the longitudinal coupling, then Stemme will develop modified parts upon demand as quickly as possible. Operation of the sailplane while the parts are being developed will not be allowed. The FAA has determined that this alternative is better than operating the sailplane with cracked parts in the flight control system.
The FAA will continue to monitor this situation, and may issue additional AD action to require mandatory replacement of modified flight control system parts other than the longitudinal coupling, as these parts become available.
Compliance Time of This AD
The replacement compliance of this AD is presented in calendar time and hours time-in-service (TIS). Cracks in the flight control system occur because of sailplane operation; however, there is a potential for corrosion in this area, which could enhance crack growth. For this reason, the FAA has determined that requiring the replacement at 6 calendar months will assure the safety of the low-usage sailplanes; and requiring the replacement at 100 hours TIS will assure the safety of the high-usage sailplanes. The prevalent compliance time will be that which occurs first.
Differences Between this AD, the Service Information, and the German AD
Stemme Service Bulletin A31-10-032, Amendment-Index 02.a, dated July 10, 1998, specifies inspecting certain areas of the flight control system coupling prior to further flight on sailplanes with over 100 hours TIS. The German AD requires this on all sailplanes registered for operation in Germany.
The FAA does not have the justification to require the initial inspection prior to further flight on all sailplanes with over 100 hours TIS. The FAA is giving a grace period of 5 hours TIS for those sailplanes that have more than 100 hours TIS on the flight control system.
Determination of the Effective Date of the AD
Since a situation exists (possible flight control system failure) that requires the immediate adoption of this regulation, it is found that notice and opportunity for public prior comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.
Comments Invited
Although this action is in the form of a final rule that involves requirements affecting immediate flight safety and, thus, was not preceded by notice and opportunity to 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 should identify the Rules Docket number and be submitted in triplicate to the address specified above. 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 No. 98-CE-106-AD." The postcard will be date stamped and returned to the commenter.
Regulatory Impact
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 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 (otherwise, an evaluation is not required). A copy of it, if filed, may be obtained from the Rules Docket.
List of Subjects in 14 CFRPart 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
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:
PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
39.13 [Amended]
2. Section 39.13 is amended by adding a new airworthiness directive (AD) to read as follows: