AD 98-24-20

This amendment adopts a new airworthiness directive (AD) that applies to certain Grob Luft-und Raumfahrt (Grob) Models G 109 and G 109B sailplanes. This AD requires inspecting the radius of the landing gear retaining bars, installing additional supportive parts, and replacing the retaining bars if the retaining bars chamfer radius is less than 3.0 millimeters (mm). This AD also requires inspecting the landing gear legs for cracks and proper thickness, and either polishing out the cracks or replacing the landing gear legs with parts of improved design depending on the crack length. This AD is the result of mandatory continuing airworthiness information (MCAI) issued by the airworthiness authority for Germany. The actions specified by this AD are intended to detect and correct fatigue cracking of the landing gear legs, which could result in landing gear failure with consequent loss of control of the sailplane during landing operations.

Final rule

98-24-20 GROB LUFT-UND RAUMFAHRT, GMBH: Amendment 39-10905, Docket No. 96-CE-40-AD.

Applicability: Models G 109 and G 109B sailplanes, all serial numbers, certificated in any category.

NOTE 1: This AD applies to each sailplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For sailplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (d) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated in the body of this AD, unless already accomplished.

To detect and correct fatigue cracking of the landing gear legs, which could result in landing gear failure with consequent loss of control of the sailplane during landing operations, accomplish the following:

(a) For all of the affected sailplanes: Within the next 120 calendar days after the effective date of this AD, inspect the retaining bars chamfer on both landing gear legs for a minimum of 3.0 millimeters (mm) radius in accordance with the "Actions" section, paragraph A3, of Grob Service Bulletin (SB) 817-39, dated January 4, 1994.

(1) If the chamfer radius is 3.0 mm or greater, prior to further flight, glue a reinforcing plastic strip (part number (P/N) 109-5000.07) to the retaining bar in accordance with the "Actions" section, paragraph A4, of Grob SB 817-39, dated January 4, 1994.

(2) If the chamfer radius is less than 3.0 mm, prior to further flight, replace the retaining bar with a new improved design retaining bar, P/N 109-5000.02; and install the plastic strip, P/N 109-5000.07. Accomplish these actions in accordance with the "Actions" section, paragraph A5, of Grob SB 817-39, dated January 1994.

(b) For sailplanes that are not equipped with landing gear legs, P/N 109B-5001.01/1: Upon the accumulation of 1,000 hours TIS on the landing gear leg or within the next 100 hours TIS after the effective date of this AD, whichever occurs later, and thereafter at intervals not to exceed 500 hours TIS, inspect the landing gear legs for cracks (using the magnetic particle or X- ray analysis method) in accordance with the "Actions" section, paragraph B9, of Grob SB 817- 39, dated January 4, 1994.

(1) If any crack(s) is found that does not exceed a maximum depth of 0.5 millimeters (mm) on each side, prior to further flight, polish out the crack(s) in accordance with the "Actions" section, paragraph B10, of Grob SB 817-39, dated January 4, 1994.

(2) If after polishing out any crack, as specified in paragraph (b)(1) of this AD, the undercarriage thickness is not at least 13 mm, prior to further flight, replace the cracked landing gear leg with a P/N 109B-5001.01/1 landing gear leg, in accordance with the "Actions" section, paragraph B10, of Grob SB 817-39, dated January 4, 1994.

(3) If any crack(s) is found that is equal to or exceeds a maximum depth of 0.5 mm on either side, prior to further flight, replace the cracked landing gear leg with a P/N 109B-5001.01/1 landing gear leg, in accordance with the "Actions" section, paragraph B10, of Grob SB 817-39, dated January 4, 1994.

(4) Replacing both landing gear legs with P/N 109B-5001.01/1 may be accomplished at any time as terminating action for the repetitive inspection requirement of this AD, but must be accomplished prior to further flight on any landing gear found cracked as specified in paragraph (b)(2) or (b)(3) of this AD.

(5) If one landing gear leg is replaced prior to further flight when a crack is found, the other landing gear leg must still be repetitively inspected every 500 hours TIS until replacement with the improved design part.

NOTE 2: Landing gear legs (P/N 109B-5001.01/1) have a "0" stamped on the front side of the leg for easy identification.

(c) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the sailplane to a location where the requirements of this AD can be accomplished.

(d) An alternative method of compliance or adjustment of the initial or repetitive compliance times that provides an equivalent level of safety may be approved by the Manager, Small Airplane Directorate, 1201 Walnut, suite 900, Kansas City, Missouri 64106. The request shall be forwarded through an appropriate FAA Maintenance Inspector, who may add comments and then send it to the Manager, Small Airplane Directorate.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Small Airplane Directorate.

(e) Questions or technical information related to Grob Service Bulletin TM 817-39, dated January 4, 1994, should be directed to Grob-Werke GmbH & Co. KG, Unternehmensbereich, Burkhart Grob Flugzeugbau, Flugplatz Mattsies, 86874 Tussenhausen, Germany. This service information may be examined at the FAA, Central Region, Office of the Regional Counsel, Room 1558, 601 E. 12th Street, Kansas City, Missouri 64106.

(f) The inspections, installation, polishing, and replacements required by this AD shall be done in accordance to Grob Service Bulletin TM 817-39, dated January 4, 1994. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Grob-Werke GmbH & Co. KG, Unternehmensbereich, Burkhart Grob Flugzeugbau, Flugplatz Mattsies, 86874 Tussenhausen, Germany. Copies may be inspected at the FAA, Central Region, Office of the Regional Counsel, Room 1558, 601 E. 12th Street, Kansas City, Missouri, or at the Office of the Federal Register, 800 North Capitol Street, NW, suite 700, Washington, DC.

(g) This amendment becomes effective on January 9, 1999.

Events Leading to the Issuance of This AD
A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that would apply to certain Grob G 109 and G 109B sailplanes was published in the Federal Register as a notice of proposed rulemaking (NPRM) on February 19, 1997 (62 FR 7373). The NPRM proposed to require inspecting the radius of the landing gear retaining bars, installing additional supportive parts, and replacing the retaining bars if the retaining bars chamfer radius is less than 3.0 mm. The NPRM also proposed to require inspecting the landing gear legs for cracks and proper thickness, and either polishing out the cracks or replacing the landing gear legs with parts of improved design depending on the crack length.

Accomplishment of the proposed action as specified in the NPRM would be required in accordance with Grob Service Bulletin TM 817-39, dated January 4, 1994.

The NPRM wasthe result of mandatory continuing airworthiness information (MCAI) issued by the airworthiness authority for Germany.

Interested persons have been afforded an opportunity to participate in the making of this amendment. No comments were received on the proposed rule or the FAA's determination of the cost to the public.

The FAA's Determination
After careful review of all available information related to the subject presented above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed except for minor editorial corrections. The FAA has determined that these minor corrections will not change the meaning of the AD and will not add any additional burden upon the public than was already proposed.

Cost Impact
The FAA estimates that 63 sailplanes in the U.S. registry will be affected by this AD.

The required inspection and modification of the retaining bars will take approximately 4 workhours per sailplane (2 workhours per landing gear leg) to accomplish, at an average labor rate of approximately $60 an hour. Parts to accomplish the required modifications cost $90. Based on these figures, the total cost impact of this inspection and modification on U.S. operators is estimated to be $20,790, or $330 per sailplane.

The initial inspection will take approximately 18 workhours per sailplane (9 workhours per landing gear leg) to accomplish, at an average labor rate of $60 per hour. Based on these figures, the total cost impact of the initial inspection on U.S. operators is estimated to be $68,040, or $1,080 per sailplane.

The above figures only take into account the costs of the initial inspection of the landing gear leg and do not take into account costs associated with repetitive inspections or any required crack polishing or landing gear leg replacement. The FAA has no way of determining the number of repetitive inspections each owner/operator of the affected sailplanes would incur, or the number of landing gear legs that will be found cracked and either need polishing or replacement.

Compliance Time
The compliance time of this AD is presented in calendar time instead of hours time-in-service (TIS). The FAA has determined that a calendar time compliance is the most desirable method because the unsafe condition of the landing gear legs described by this AD is caused by corrosion. Corrosion initiates as a result of sailplane operation, but can continue to develop regardless of whether the sailplane is in service. In order to assure that the above-referenced condition is detected and corrected on all sailplanes within a reasonable period of time without inadvertently grounding any sailplanes, the FAA is requiring a compliance schedule based upon calendar time instead of hours TIS.

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.

For the reasons discussed above, I certify that this action (1) is not a " significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A copy of the final evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption "ADDRESSES".

List of Subjects in 14 CFR Part 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: