Events Leading to the Issuance of This AD
Has FAA taken any action to this point? An incident where the propeller blade suspension fork failed during flight on a Stemme Model S10-V sailplane caused FAA to issue AD 98-15-24, Amendment 39-10674. This AD was published in the Federal Register on July 23, 1998 (63 FR 39484), and required replacing the propeller blade suspension fork, distance ring, and nut with parts of improved design on Stemme Model S10-V sailplanes.
After issuing AD 98-15-24, the Luftfahrt-Bundesamt (LBA), which is the airworthiness authority for Germany, notified FAA that the improved design propeller blade suspension fork (part number (P/N) A09-10AP-V08) on one of the affected sailplanes failed during flight. Analysis of this propeller blade revealed a fracture located at the end of the threaded fastening pin. This caused FAA to issue a proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include anAD that would apply to all Stemme Models S10-V and S10-VT sailplanes that incorporate a certain propeller blade suspension fork. This proposal was published in the Federal Register as a notice of proposed rulemaking (NPRM) on July 21, 1999 (64 FR 39100).
The NPRM proposed to supersede AD 98-15-24 with a new AD that would require you to repetitively exchange (through the manufacturer) the P/N A09-10AP-V08 (or FAA-approved equivalent part number) propeller blade suspension fork for a fork that has passed X-ray crack testing requirements.
Was the public invited to comment on the NPRM? The FAA invited interested persons to participate in the making of the amendment. We received no comments on the proposed rule or the cost impact upon the public. However, the LBA has informed us that the existing propeller blade suspension forks are currently cracking more rapidly than originally projected.
Is there a propeller blade suspension fork design that is better than the current design? Stemme has worked with the LBA in designing an improved propeller blade suspension fork (P/N 10AP-V88) along with a modification to the propeller gearbox suspension.
Has the manufacturer issued service information? Stemme issued Service Bulletin No. A31-10-051, Amendment-Index 05.a, dated December 6, 1999. This service bulletin specifies procedures for accomplishing the propeller blade suspension fork replacement and propeller gearbox suspension modification, which were described previously.
The FAA's Determination and Follow-up Action
What have we decided? After careful review of all available information related to the subject presented above, including the above-referenced comments, FAA has determined that:
- the propeller blade suspension fork replacement and propeller gearbox suspension modification should be accomplished on all Stemme Models S10-V and S10-VT sailplanes; and
- AD action should be taken to prevent certain propeller blade suspension forks from cracking, which could result in the loss of a propeller blade during flight with possible lateral imbalance and loss of thrust.
What is our next action? Since the improved design propeller blade suspension fork replacement and propeller gearbox suspension modification requirements increase the burden on the owners/operators of the affected sailplanes over what was proposed in the NPRM, we are required to allow the public additional time to comment on the AD.
Because of the low hours TIS on the sailplanes where the cracked propeller blade suspension forks were found, FAA finds that notice and opportunity for public prior comment are impracticable. Therefore, good cause exists for making this amendment effective in less than 30 days.
What does this AD require? This AD requires you to:
- remove the propeller blade suspension forks;
- exchange them with the manufacturer for improved design forks; and
- install the improved design propeller blade suspensionforks.
Accomplishment procedures are specified in Stemme Service Bulletin No. A31-10-051, Amendment- Index 05.a, dated December 6, 1999.
Comments Invited
Can I comment on this AD? This action is in the form of a final rule and the FAA did not precede it with notice and opportunity for public comment. FAA is issuing this final rule without prior notice because an urgent situation concerning safety of flight exists. However, FAA is still inviting comments on this rule. You may submit whatever written data, views, or arguments you choose. You need to include the rule's docket number and submit your comments in triplicate to the address specified under the caption "ADDRESSES." The FAA will consider all comments received on or before the closing date. We may amend this rule in light of comments received.
How can we communicate more clearly with you? The FAA is reviewing the writing style we currently use in regulatory documents, in response to the Presidential memorandum of June 1, 1998. That memorandum requires federal agencies to communicate more clearly with the public. We are interested in your comments on the ease of understanding this document, and any other suggestions you might have to improve the clarity of FAA communications that affect you. You can get more information about the Presidential memorandum and the plain language initiative at http://www.faa.gov/language/.
The FAA specifically invites comments on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. You may examine all comments we receive before and after the closing date of the rule in the Rules Docket. We will file a report in the Rules Docket that summarizes each FAA contact with the public that concerns the substantive parts of this AD.
How can I be sure the FAA receives my comment? If you want us to acknowledge the receipt of your comments, you must include a self-addressed, stamped postcard. On the postcard, write "Comments to Docket No. 99-CE-25-AD." We will date stamp and mail the postcard back to you.
Regulatory Impact
How does this AD impact relations between Federal and State governments? These regulations will not have a substantial direct effect 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. The FAA has determined that this final rule does not have federalism implications under Executive Order 13132.
How does this action involve an emergency situation? 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. We have determined that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If FAA determines that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, we will prepare a final regulatory evaluation. You may obtain a copy of the evaluation (if required) from the Rules Docket.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by Reference, Safety.
Adoption of the Amendment
Accordingly, under 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. FAA amends Section 39.13 by removing Airworthiness Directive (AD) 98-15-24, Amendment 39-10674 (39484, July 23, 1998), and by adding a new AD to read as follows: