AD 99-17-12

This amendment adopts a new airworthiness directive (AD), applicable to certain British Aerospace Model BAe 146 and Model Avro 146-RJ series airplanes, that requires a one-time measurement to determine the thickness of the outer links of the side stays of the main landing gear (MLG), and corrective actions, if necessary. This amendment also provides for replacement of a thin outer link with a new or serviceable part in lieu of certain follow-on inspections. This amendment is prompted by issuance of mandatory continuing airworthiness information by a foreign civil airworthiness authority. The actions specified by this AD are intended to prevent cracking of the outer links of the side stays of the MLG, which could result in failure of a side stay, and consequent collapse of the landing gear.

Final rule

99-17-12 BRITISH AEROSPACE REGIONAL AIRCRAFT (Formerly British Aerospace Regional Aircraft Limited, Avro International Aerospace Division; British Aerospace, PLC; British Aerospace Commercial Aircraft Limited): Amendment 39-11260. Docket 97-NM-129-AD. Issued August 10, 1999.
Applicability: Model BAe 146 and Model Avro 146-RJ series airplanes, equipped with side stays of the main landing gear (MLG) having part numbers (P/N) listed in Messier-Dowty Service Bulletin 146-32-128, dated December 6, 1996; certificated in any category.

NOTE 1: This AD applies to each airplane 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 airplanes 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 (c) 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, unless accomplished previously.

To prevent cracking of the outer links of the side stays of the main landing gear (MLG), which could result in failure of a side stay, and consequent collapse of the landing gear; accomplish the following:

(a) Within 500 landings or 60 days after the effective date of this AD, whichever occurs later, perform a one-time measurement to determine the thickness of the outer links of the side stays of the MLG, in accordance with British Aerospace Service Bulletin SB.32-144, dated December 11, 1996.

NOTE 2: The British Aerospace service bulletin references Messier-Dowty Service Bulletin 146-32-128, dated December 6, 1996, as an additional source of service information for accomplishment of the measurement.

(1) If the profile gauge does not slip over the top edge of the outer link profile, no further action is required by this AD.

(2) If the profile gauge slips over the top edge of the outer link profile, prior to further flight, accomplish either paragraph (a)(2)(i) or (a)(2)(ii) of this AD.

(i) Replace the outer link with a new or serviceable part in accordance with the service bulletin. After replacement of the outer link, no further action is required by this AD.

NOTE 3: For purposes of this AD, a "serviceable" outer link is defined as an outer link that is not cracked and on which a profile gauge does not slip over the top edge of the profile, as described in the service bulletin.

(ii) Perform a detailed visual inspection to detect cracking of the outer links of the side stays of the MLG, in accordance with the service bulletin.

NOTE 4: For the purposes of this AD, a detailed visual inspection is defined as: "As intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required."

(A) If no cracking is detected, repeat the detailed visual inspection thereafter at intervals not to exceed 4,000 landings.

(B) If any cracking of only one flange of an outer link is detected, and the cracking is within the limits specified by the service bulletin: Repeat the detailed visual inspection at intervals not to exceed 70 landings, and replace the cracked outer link with a new or serviceable part in accordance with the service bulletin within 500 landings after the cracking is detected. After replacement of the outer link, no further action is required by this AD.

(C) If any cracking of more than one flange of an outer link is detected, or if any cracking is detected that is outside the limits specified by the service bulletin: Prior to further flight, replace the cracked outer link with a new or serviceable part in accordance with the service bulletin. After replacement of the outer link, no further action is required by this AD.

(b) As of the effective date of this AD, no person shall install on any airplane a side stay of the MLG having a part number listed in paragraph 1.A. of Messier-Dowty Service Bulletin 146-32-128, dated December 6, 1996; unless the profile gauge does not slip over the profile of the outer links of the side stay, as described in British Aerospace Service Bulletin SB.32-144, dated December 11, 1996.

Alternative Methods of Compliance
(c) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, International Branch, ANM-116, FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, International Branch, ANM-116.

NOTE 5: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the International Branch, ANM-116.

Special Flight Permits
(d) 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 airplane to a location where the requirements of this AD can be accomplished.

Incorporation by Reference
(e) The actions shall be done in accordance with British Aerospace Service Bulletin SB.32-144, dated December 11, 1996. 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 AI(R) American Support , Inc., 13850 Mclearen Road, Herndon, Virginia 20171. Copies may be inspected 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.

NOTE 6: The subject of this AD is addressed in British airworthiness directive 005-12-96.

(f) This amendment becomes effective on September 27, 1999.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain British Aerospace Model BAe 146 and Model Avro 146-RG series airplanes was published in the Federal Register on September 8, 1998 (63 FR 47445). That action proposed to require a one-time measurement to determine the thickness of the outer links of the side stays of the main landing gear (MLG), and corrective actions, if necessary. That action also proposed to provide for replacement of a thin outer link with a new or serviceable part in lieu of certain follow-on inspections.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Request to Allow Flight with Cracks
One commenter, the manufacturer, requests that the proposal be revised to allow flight with certain specified crackinglimits. The commenter points out that, although the inspection for cracking is easily accomplished, the replacement of a cracked part is difficult (necessitates acquisition of the replacement part and takes about 12 hours of elapsed time for the installation). The commenter states that a side stay with a 1 millimeter (mm) crack in the outer links of the side stays of the MLG was returned to the commenter, and was then subjected to fatigue testing by applying 20,000 cycles of the test spectra, where 1 cycle of test spectra was equivalent to 1 flight. The crack grew to 30 mm in length. The side stay was then tested to 130 percent and finally to 165 percent of limit load without failure (i.e., in excess of ultimate load). The commenter notes that, based on those fatigue testing results, the United Kingdom Civil Aviation Authority (CAA) granted approval for continued revenue service with cracking detected up to 19.05 mm, and required inspections to detect cracking at intervals of 70 landings, up to a maximum of 500 landings.

The FAA concurs with the commenter s request in this case. Since the outer link of the main landing gear side stay is readily inspectable for cracking during the normal operation of the airplane, the FAA has determined that cracking could be discovered at a remote site, but that acquiring parts and accomplishing the repair would be difficult. In addition, the FAA has determined that the commenter has provided a conservative demonstration that the airplane can retain FAA-certificated strength requirements for a limited period of time until the cracked part is replaced. Therefore, continued flight of the airplane may be permitted when cracking exists that is within the limits described in the service bulletin, provided that visual inspections for cracking and eventual replacement of the cracked part are performed at the times specified in the final rule. The FAA has revised paragraph (a)(2)(ii)(B) of the final rule and added a new paragraph (a)(2)(ii)(C) to the final rule that reflect these changes.

Request to Revise the Unsafe Condition
This same commenter notes that while the proposal states that cracking of the outer links of the side stays of the MLG could "result in increased braking distance during landing and consequent runway overrun," the actual unsafe condition is that the cracking could result in failure of the side stay, which would result in collapse of the main landing gear.

The FAA infers that the commenter is requesting that the unsafe condition be revised. The FAA acknowledges that, although the proposal describes one possible unsafe outcome of a main landing gear collapse, other unsafe outcomes are possible. The FAA concurs that, in this case, the commenter s suggested revision is preferable to the proposal s description in that it is a more precise statement of the actual consequence of cracking of the outer links of the side stays of the MLG. The FAA has revised the final rule toreflect the commenter s suggestion.

In addition, the FAA has added a new "NOTE 4" to the final rule to add a definition of the term "detailed visual inspection."

Conclusion
After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes described previously. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

Cost Impact
The FAA estimates that 37 Model BAe 146 and Model Avro 146-RJ series airplanes of U.S. registry will be affected by this AD. It will take approximately 1 work hour per airplane to accomplish the required measurement, at an average labor rate of $60 per work hour. Required parts will be supplied by the manufacturer at no cost to operators. Based on this figure, the cost impact of the measurement required by this AD on U.S. operators is estimated to be $2,220, or $60 per airplane.

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.

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 final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from 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 the following new airworthiness directive: