Airworthiness Directives; Boeing Model 737-600, -700, -700C, -800, and -900 Series Airplanes

Summary:

The FAA is superseding an existing airworthiness directive (AD), which applies to all Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. That AD currently requires either determining exposure to runway deicing fluids containing potassium formate, or performing repetitive inspections of certain electrical connectors in the wheel well of the main landing gear (MLG) for corrosion, and follow-on actions. This new AD adds a new inspection requirement and related corrective actions. This AD is prompted by additional reports indicating that significant corrosion of the electrical connectors in the wheel well of the MLG has also been found on airplanes that land on runways treated with deicing fluids containing potassium acetate. We are issuing this AD to prevent corrosion and subsequent moisture ingress into the electrical connectors, which could result in an electrical short and consequent incorrect functioning of critical airplane systems essential to safe flight and landing of the airplane, including fire warning systems.

Table of Contents

Addresses:

The service information referenced in this AD may be obtained from Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207.

Docket: The AD docket contains the proposed AD, comments, and any final disposition. You can examine the AD docket on the Internet at http://dms.dot.gov, or in person at the Docket Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone (800) 647-5227) is located on the plaza level of the Nassif Building at the U.S. Department of Transportation, 400 Seventh Street, SW., room PL-401, Washington, DC. This docket number is FAA-2004-19750; the directorate identifier for this docket is 2003-NM-192-AD.

For further information contact:

Binh Tran, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 917-6485; fax (425) 917-6590.

Supplementary information:

The FAA proposed to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) with an AD to supersede AD 2002-16-03, amendment 39-12842 (67 FR 52396, August 12, 2002). The existing AD applies to all Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. The proposed AD was published in the Federal Register on December 1, 2004 (69 FR 69832), to require either determining exposure to runway deicing fluids containing potassium formate or performing repetitive inspections of certain electrical connectors in the wheel well of the main landing gear (MLG) for corrosion, and follow-on actions.

Comments

We provided the public the opportunity to participate in the development of this AD. We have considered the comments that have been submitted on the proposed AD.

Requests for Credit/Extension of Compliance Time for Previous Inspections

Three commenters ask that the proposed AD be changed to allow credit for the repetitive inspections being accomplished per the existing AD. The first commenter states that it has been in compliance with the existing AD by performing the repetitive inspections of the electrical connectors, as specified in paragraph (f)(1)(ii) of the proposed AD, every 12 calendar months. The commenter notes that it chose to perform this inspection instead of determining exposure to runway deicing fluids containing potassium formate because it cannot establish whether airplanes that fly into unfamiliar airports have been exposed. The commenter adds that, based on the current language in the proposed AD, all of its airplanes would have to be re-inspected before further flight if exposed to potassium formate. The commenter states that there is no safety-of-flight issue if the airplane is already being repetitively inspected per the existing AD; therefore, operations should be continued as long as the requirements in paragraph (f)(2) of the proposed AD (i.e., repetitive detailed inspections and follow-on actions) are met. The commenter concludes that airplanes on which the inspections have been performed in the last 12 months before issuance of the proposed AD should be exempt from performing another inspection before further flight.

The second commenter states that the proposed AD does not clearly give credit for previous compliance with the existing AD.

The third commenter asks that, if the FAA proceeds with issuance of the proposed AD, all aircraft that have previously complied with the existing AD via detailed inspection of the electrical connectors, or per an approved alternative method of compliance (AMOC), not be required to perform the inspection for at least 12 months after performing the last inspection required by the existing AD.

We agree that the commenters should get credit for the detailed inspections accomplished per the original issue of the service bulletin (which was referenced in the existing AD as the appropriate source of service information for accomplishing the detailed inspections of the electrical connectors). We have added a new paragraph (g) to this final rule to give such credit. Additionally, we have changed the final rule to specify that operators are allowed to do the actions specified in either paragraph (f)(1) or (f)(2) of the final rule at intervals not to exceed 12 months, regardless of airplane exposure. However, we have changed the compliance time for accomplishing the detailed inspection for airplanes that have been exposed to potassium formate or potassium acetate to 90 days after that determination is made (and thereafter at intervals not to exceed 12 months). The proposed AD specified accomplishing the detailed inspection before further flight for airplanes that have been exposed to potassium formate or potassium acetate, but we have added a 90-day grace period before the detailed inspection on those airplanes must be accomplished. We have determined that accomplishing the detailed inspection within 90 days represents an acceptable interval of time wherein affected airplanes may be allowed to operate without jeopardizing safety.

One commenter notes that paragraph (f)(1)(ii) of the proposed AD requires performing the inspection required by paragraph (f)(2) of the proposed AD before further flight, and that this compliance time is troublesome. The commenter states that it would ground some airplanes upon the effective date of the AD until the detailed inspection is accomplished. The commenter adds that operators have not previously been required to determine airplane exposure to potassium acetate, and no time is given to make such a determination in the proposed AD. The commenter states that this is further complicated by the fact that credit should be given for compliance with the existing AD.

A second commenter states that, in order to comply with paragraph (f)(1) of the proposed AD, it would be necessary to have written evidence of the runway cleaning assessment from airport management when deicing fluids are used due to meteorological events. The commenter adds that to perform the inspection required by paragraph (f)(2) before further flight is very restrictive if the flight is made with intermediate legs, which could cause delays. The commenter notes that it would be better to have more time to accomplish this inspection.

A third commenter states that its partner airline must obtain a change or an AMOC to paragraph (f)(1)(ii), described previously. The commenter states that, if its partner airline cannot get the compliance time extended to 6 months or so, it will be required to do the 8-hour inspection on the same day they determine exposure, which will ground those airplanes until the inspection is done.

We partially agree with the commenters. We have already extended the compliance time for accomplishing the initial detailed inspection of airplanes that have been exposed to potassium formate or potassium acetate to 90 days, as specified above. Additionally, operators may incorporate a repetitive inspection program in lieu of determining exposure to runway deicing fluids; therefore, it is not necessary for us to obtain written evidence of the runway cleaning assessment from airport management. We have made no change to the final rule in this regard.

One commenter states that paragraph (f)(2) of the proposed AD requires operators to perform an airplane exposure review every 12 months, per paragraph (f)(1) of the proposed AD. The commenter adds that this yearly review should not be required for operators that choose to inspect their airplanes every 12 months, regardless of airplane exposure. The commenter asks that the last sentence of paragraph (f)(2) be changed to read “Repeat the actions required by paragraph (f)(1) or (f)(2) of this AD thereafter at intervals not to exceed 12 months.”

We agree with the commenter. However, we have removed the repetitive interval specified in paragraph (f)(2) of the proposed AD and added the repetitive interval to paragraph (f) of this final rule. By adding the repetitive interval to the main paragraph, the actions for both paragraphs (f)(1) and (f)(2) of the final rule are covered. Paragraphs (f)(1)(i) and (f)(1)(ii) of the proposed AD identify airplanes that have not, and have, respectively, been exposed to potassium formate or potassium acetate.

Request To Extend Repetitive Inspection Interval

Two commenters ask that the repetitive inspection interval specified in the proposed AD be extended.

One commenter states that it has completed three series of inspections per the existing AD, and at the time of its last inspection, its fleet had accumulated over 691,000 flight hours and 369,000 flight cycles with no findings. The commenter states that the manufacturer provided no technical objection to its request to extend the repetitive inspection interval in the existing AD from 12 to 24 months. The commenter asks that the repetitive inspection interval specified in the proposed AD be extended to 24 months.

The second commenter states that the manufacturer has determined that the amount of corrosion to be expected is dependent on the number of landings on runways where potassium-based deicing fluids are used. The commenter notes that not all operators have thesame quantity of flights to affected runways, yet, as proposed, operators with little exposure are subject to the same restrictive interval as operators in highly exposed regions. The commenter operates the majority of the affected 737NG (next generation) airplanes with flights mostly on eastern, western, and southern routes, and there is little exposure to deicing fluids on these routes; although the possibility of some exposure exists. The commenter asks that the repetitive interval be 12 months for airplanes with high exposure, and extended to 24 months for airplanes with medium exposure, and 36 months for airplanes with limited exposure.

We do not agree with the commenters' requests. We have not received any verification showing that the amount of corrosion on the connectors can last through two winters (24 months) without affecting safety of flight, or that airplanes with limited exposure can resist corrosion for longer periods of time when exposed to deicing fluids containing potassium formate and potassium acetate. In addition, no technical justification was provided that verifies extending the repetitive inspection interval will still maintain an appropriate level of safety. In developing an appropriate compliance time for this proposed AD, we considered safety issues as well as the recommendations of the manufacturer and the practical aspects of accomplishing the required inspections within an interval of time that corresponds to the normal maintenance schedules of most affected operators. We do not find it necessary to change this final rule in this regard.

Request for Information/Clarification for Determining Airplane Exposure

Two commenters ask that the phrase “determine airplane exposure,” as specified in the proposed AD, be further clarified.

One commenter notes that the proposed AD would require either determining exposure to runway deicing fluids containing potassium formate or potassium acetate, or performing repetitive inspections of certain electrical connectors. The commenter states that affected operators have no authority or control over airports, but the FAA has the authority to require airports to provide the information that would be necessary for determination of airplane exposure. The commenter cites Title 14, Aeronautical and Space, Part 139—Certification of Airports—Subpart D—Operations, Federal Aviation Regulation (FAR) 139.310(c), Records, and FAR 139.313(a), Snow and Ice Control, and adds that snow and ice control plans for most U.S. airports are authorized by the FAA. The commenter asks that the data necessary to make this determination be provided to all affected operators by the FAA.

Another commenter states that it would be very helpful if the FAA would provide a written definition of what constitutes airplane exposure. The commenter states that information it received from the FAA in late 2002 defined exposure as “Landing at or taking off from an airport where subject runway deicing fluid or pelletized solid had been applied anytime during the previous 365 days.” The commenter believes, “as most of the airline industry does,” that this is far too broad an exposure window since the applied fluid will wash away, or will dry up and blow away, within a week or so after application. The commenter adds that testing of the pelletized forms of the subject deicers has shown to be less corrosive to airplanes.

We partially agree with the commenters. The Airport Safety and Operations Division (AAS-300) of the FAA issued CertAlerts No. 01-04 and No. 02-02 to instruct airport operators to inform and coordinate the use of such chemicals with air carriers. The CertAlerts state that the airplane operators may contact airport operators to obtain information about deicing materials used on runways. We have made no change to the final rule in this regard.

Request To Include Related Service Information

One commenter states that, since Boeing Service Bulletin 737-24-1149, Revision 2, dated August 14, 2003, also addresses corrosion protection of the electrical connectors in the main wheel well, and those connectors are specified in the service information referenced in the proposed AD, that service bulletin should be required in the final rule. The commenter adds that granular potassium nitrate is a commonly used deicing product on airport ramp and gate areas; when this product dissolves into a solution by the melted ice and snow, it could splatter into the wheel well areas during taxi and takeoff.

We do not agree with the commenter's request. The commenter did not provide supporting data regarding the effects of granular potassium nitrate. We have determined that further delay of this final rule is not appropriate; however, we are planning to review Boeing Service Bulletin 737-24-1149 and may then consider further rulemaking action on the issue of deicing. We have made no change to the final rule in this regard.

Request To Change Costs of Compliance Section

Several commenters ask that the work hours and cost specified in the “Costs of Compliance” section be changed.

The first commenter states that it estimates the time to accomplish the actions at 5 work hours; this adds aircraft out-of-service costs to the labor and materials estimated in the proposed AD. The commenter adds that, for a limited-exposure operator, the added out-of-service costs are not warranted, and additional operational costs to the airlines in this economic environment, based on the most exposed operator condition, adds an undue burden on the industry.

The second commenter states that the estimated cost for the determination of airplane exposure is a poor labor cost estimate. The commenter adds that the estimate in the proposed AD is based on the number of airplanes operated and not on the number of airports being used by affected operators; the location and number of airports utilized by affected operators also need to be considered to more accurately determine the costs. The commenter notes that no estimated costs are specified for the required repetitive detailed inspections and any necessary corrective actions that will be required on a percentage of affected airplanes. The commenter gives an example, based on its experience, of labor costs for the inspection, corrective actions, parts cost for new connectors, cost for corrosion-inhibiting compound, and parts cost for consumables utilized during maintenance.

The third commenter estimates that it takes at least 8 elapsed work hours and 24 work hours per airplane to comply with the actions in both the proposed and existing AD. The commenter adds that the proposed AD is presently costing over $230,000 annually for its 139 affected airplanes, and not the $9,035 annual total specified in the proposed AD.

We partially agree with the commenters.

We agree that the cost for the detailed inspection should be added to the final rule because we have changed the actions in the final rule to give operators the option of performing either the determination of exposure or the detailed inspection of the electrical connectors. The “Costs of Compliance” section has been changed accordingly.

We do not agree to add to the final rule the cost for estimated time or for corrective actions if any discrepancy is found. The actions in this final rule reflect only the direct costs of thespecific required actions based on the best data available from the manufacturer. We recognize that operators may incur incidental costs (such as the time for planning, access and close, and associated administrative actions) in addition to the direct costs. The cost analysis in ADs, however, typically does not include incidental costs or the cost for on-condition corrective actions. The compliance times in this AD should allow ample time for operators to do the required actions at the same time as scheduled major airplane inspection and maintenance activities, which would reduce the additional time and costs associated with special scheduling.

Additionally, we do not agree that the location and number of airports utilized should be considered to more accurately determine the costs. The operational cost of airports utilized may vary significantly from operator to operator; therefore, individual costs for the location and number of airports utilized is almost impossible to calculate.

Request for Credit for AMOCs Approved for Existing AD

Two commenters ask that previously issued AMOCs for the existing AD continue to be approved for the proposed AD.

The first commenter asks that two specific approved AMOCs be acceptable for compliance with the proposed AD. One AMOC extended the compliance time to 90 days for accomplishing the procedures described in paragraphs (a)(1)(i) and (b) of the existing AD (which are not restated in the proposed AD). The other AMOC defined an acceptable corrosion area as 10% of the total area of the backshell of the connectors. The commenter adds that the second AMOC also allows connector replacement when the total amount of corrosion is between 10% and 30%. The commenter recommends that these AMOCs remain valid.

The second commenter notes that it is already in compliance with the proposed AD and requires no change in its current method of compliance. The commenter adds that it was granted six AMOC approvals by the Seattle Aircraft Certification Office for accomplishing the existing AD's annual repetitive inspections (which currently are required on 139 airplanes). The commenter states that there should be no technical or operational reason that existing AMOCs cannot be applied to the proposed AD, because Revision 1 of the service bulletin, which was referenced in the proposed AD as the appropriate source of service information for accomplishing the actions, contains the same actions as the original issue. The commenter concludes that, if necessary, it will re-submit the original and approved AMOC request letters to the FAA requesting the same or parallel AMOCs for the proposed AD.

We do not agree with the commenters' requests. As specified in the proposed AD, AMOCs approved previously in accordance with AD 2002-16-03, amendment 39-12842, are not approved as AMOCs with this AD because of the addition of a new requirement to determine airplane exposure to potassium acetate. Additionally, although certain AMOCs extended the compliance time for corrective actions, the corrective actions are normally performed before further flight, so that the extension was an exception to normal procedures. The actions in this final rule have been changed, as stated previously, to allow 12 months for repeating either the determination of airplane exposure or the detailed inspection of the electrical connectors, as well as to allow 90 days to perform the detailed inspection for airplanes that have been exposed to potassium formate and/or potassium acetate. However, any additional corrective actions must be performed before further flight. The approval for replacement of the connectors if the area of corrosion is greater than ten percent of the total backshell surface area has been incorporated into the revised service information referenced in this final rule. We have made no change to the final rule in this regard.

Request To Change Certain Requirements

One commenter reiterates the requirements in paragraph (f)(2) of the proposed AD and states that this paragraph would require all affected airplanes that were not inspected per Part 1, but were inspected per Part 2, of the original issue of Boeing Service Bulletin 737-24A1148 (referenced in the existing AD for accomplishing certain actions), to be re-inspected per Part 1 of Revision 1 of the service bulletin, because of the wording “by doing all the actions.” The commenter adds that, since airplanes that were inspected per Part 2 of the original issue meet the full intent of the existing AD, the requirement to accomplish Part 1 of Revision 1 should not be mandated.

We agree with the commenter. The intent of this final rule is essentially the same as that of the existing AD, but the proposed AD adds an inspection for potassium acetate. The requirements in this AD are based on the latest information provided by the manufacturer; therefore, the Accomplishment Instructions of Revision 1 of the service bulletin should be followed. As stated previously, we have added a credit paragraph for inspections already done per the existing AD using the original issue of the service bulletin, and that when the inspections are repeated, Revision 1 of the service bulletin must be used.

Request To Provide Terminating Action

Several commenters ask that a terminating action for the repetitive inspections specified in the proposed AD be developed.

One commenter states that operators need the manufacturer and the FAA to aggressively address the development of a terminating action for the repetitive inspections. The commenter adds that, because there have been no electrical connector problems, as well as limited and declining corrosion findings fleet-wide during two annual inspections, it formally requested from the manufacturer that it extend the repetitive inspection interval from 12 to 18 or 24 months, during the time they are developing a terminating action for the proposed AD. The commenter is awaiting new information from the manufacturer regarding newly designed thrust reverser (TR) cascades and electrical connectors made of improved stainless steel and anodized aluminum, which would be installed in all ten positions. The commenter suggests that the combination of installing improved TR cascades, replacing the existing connectors with new connectors, and applying corrosion inhibiting compound, by following the new service information to be issued by the manufacturer (depending on FAA analysis and acceptance) be designated as a terminating action for the repetitive inspections. The commenter adds that the cost for the terminating action could be considerable, but if this action terminates the repetitive inspections, it would save the commenter over $230,000 annually, as the present cost for the inspection is about $3.3 million.

The second commenter states that the manufacturer is collecting data from operators to propose a more convenient maintenance interval for the mandated inspections. The commenter asks that the FAA consider both a maintenance interval based on operations on affected runways, and possible terminating action, prior to publishing the final rule.

We agree that a terminating action for the repetitive inspections would benefit operators. The airplane manufacturer is currently developing a terminating action. Once the proposed terminating action has been submitted to us forreview, and we have approved the proposed action as terminating action for the requirements of the AD, anyone may apply for approval to use that terminating action as an AMOC under the provisions of paragraph (h)(1) of this final rule.

The third commenter states that terminating action is possible and requests that the FAA implement all of the following solutions. The FAA's response follows each comment.

• Withdraw the proposed AD.

We do not agree that we should withdraw the proposed AD until a terminating action is developed. We do not consider it appropriate to delay the issuance of this final rule in light of the identified unsafe condition. Additionally, we do not have any technical justification to withdraw the proposed AD, and the repetitive inspections are required for continued safe flight of the airplane. Therefore, we have made no change to the final rule in this regard.

• Determine changes that need to be made to the specifications for deicing materials used at airports under FAA authority and control to eliminate the subject corrosion. Ensure adequate improvements are made to the deicing material specifications, and then mandate to airports under FAA authority and control that only these improved deicing materials be used as part of FAA-authorized snow and ice removal plans under FAA regulations.

The specifications for deicing fluids are determined by the Society of Automotive Engineers (SAE) G-12 Aircraft Ground Deicing Fluids Subcommittee, and the FAA enforces those deicing specifications under FAA regulations. We are working with the SAE subcommittee (we participate in this committee) to ensure that adequate improvements are made to the deicing material specifications.

• Direct Boeing to determine which design changes need to be made to the 737NG airplanes in order to eliminate unique susceptibility to the corrosive effects of runway deicing materials. Promulgate an AD requiring incorporation of the design changes determined to be necessary for the 737NG airplanes, in order to eliminate the subject corrosion problem within its MLG wheel wells.

We have determined that the repetitive inspections required by this final rule will maintain an adequate level of safety for all affected airplanes until a terminating action is developed. As specified previously, the manufacturer is currently developing a terminating action for the repetitive inspections. After terminating action is developed, approved, and available, we may consider further rulemaking action. The terminating action should provide a solution to both the corrosive effects of runway deicing materials and corrosion in the MLG wheel wells.

Request To Address Technical Objection

One commenter states that it has previously objected to the manufacturer and the FAA * * * * and still stands by this objection in principle * * * regarding the unwarranted detailed inspection of the electrical connectors. The commenter notes that the subject inspection is an imprudent practice, since routinely opening cannon-plug connectors on so many airplanes without any indication of problems could create a risk of pushing back or bending connector pins. This would leave a less secure seal that could allow the ingress of moisture in the future.

We infer that the commenter wants the requirement for repetitive detailed inspections removed from the final rule. As explained in the preamble of the proposed AD, we have received reports of significant corrosion of the electrical connectors located in the wheel well of the MLG on Model 737 series airplanes that land on runways treated with deicing fluids containing potassium acetate. We have determined that the detailed inspections required by the existing AD do not account for exposure to deicing fluids containing potassium acetate. Therefore, we find that repetitive detailed inspections are necessary to prevent corrosion and subsequent moisture ingress into the electrical connectors, which could result in an electrical short and consequent incorrect functioning of critical airplane systems essential to safe flight and landing of the airplane, including fire warning systems. We have made no change to the final rule in this regard.

Conclusion

We have carefully reviewed the available data, including the comments that have been submitted, and determined that air safety and the public interest require adopting the AD with the changes described previously. We have determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

Costs of Compliance

This AD affects about 587 airplanes of U.S. registry.

The new determination of airplane exposure takes about 1work hour per airplane, at an average labor rate of $65 per work hour. Based on these figures, the estimated cost of the determination of airplane exposure specified in this AD for U.S. operators is $38,155, or $65 per airplane, per cycle.

The detailed inspection takes about 1work hour per airplane, at an average labor rate of $65 per work hour. Based on these figures, the estimated cost of the detailed inspection specified in this AD for U.S. operators is $65 per airplane, per inspection cycle.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in subtitle VII, part A, subpart III, section 44701, “General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

Regulatory Findings

We have determined that this AD will not have federalism implications under Executive Order 13132. This AD 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.

For the reasons discussed above, I certify that this AD:

(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.

We prepared a regulatory evaluation of the estimated costs to comply with this AD. See the ADDRESSES section for a location to examine the regulatory evaluation.

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 FAA amends 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 2. The FAA amends § 39.13 by removing amendment 39-12842 (67 FR 52396, August 12, 2002), and by adding the following new airworthiness directive (AD):

2005-18-23Boeing: Amendment 39-14264. Docket No. FAA-2004-19750; Directorate Identifier 2003-NM-192-AD.

Effective Date

(a) This AD becomes effective October 19, 2005.

Affected ADs

(b) This AD supersedes AD 2002-16-03, amendment 39-12842.

Applicability:(c) This AD applies to all Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes; certificated in any category.

Unsafe Condition

(d) This AD was prompted by additional reports indicating that significant corrosion of the electrical connectors in the wheel well of the MLG has also been found on airplanes that land on runways treated with deicing fluids containing potassium acetate. We are issuing this AD to prevent corrosion and subsequent moisture ingress into the electrical connectors, which could result in an electrical short and consequent incorrect functioning of critical airplane systems essential to safe flight and landing of the airplane, including fire warning systems.

Compliance:(e) You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.

Determine Airplane Exposure/Significant Corrective Actions

(f) Within 12 months after the effective date of this AD: Perform the actions required by either paragraph (f)(1) or (f)(2) of this AD.

(1) Determine airplane exposure to runway deicing fluids containing potassium formate or potassium acetate by reviewing airport data on the type of components in the deicing fluid used at airports that support airplane operations.

(i) If the airplane has not been exposed, repeat the requirements specified in paragraph (f)(1) of this AD thereafter at intervals not to exceed 12 months.

(ii) If the airplane has been exposed, within 90 days after that determination is made, do the inspection required by paragraph (f)(2) of this AD; and repeat the inspection thereafter at intervals not to exceed 12 months.

(2) Do a detailed inspection of the electrical connectors, including the contacts and backshells, of the line replaceable unit (LRU) in the wheel well of the MLG for corrosion by doing all the actions in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-24A1148, Revision 1, dated July 10, 2003. Do any significant/corrective actions before further flight in accordance with the service bulletin.

Note 1:

For the purposes of this AD, a detailed inspection is defined as: “An 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.”

Inspections Accomplished Previously

(g) Inspections accomplished before the effective date of this AD in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-24A1148, dated December 6, 2001, are acceptable for compliance with the inspections required by paragraph (f)(2) of this AD.

Alternative Methods of Compliance (AMOCs)

(h)(1) The Manager, Seattle Aircraft Certification Office, FAA, has the authority to approve AMOCs for this AD, if requested in accordance with the procedures found in 14 CFR 39.19.

(2) AMOCs approved previously in accordance with AD 2002-16-03, amendment 39-12842, are not approved as AMOCs with this AD.

Material Incorporated by Reference

(i) You must use Boeing Alert Service Bulletin 737-24A1148, Revision 1, dated July 10, 2003, to perform the actions that are required by this AD, unless the AD specifies otherwise. The Director of the Federal Register approves the incorporation by reference of this document in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. To get copies of the service information, contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207. To view the AD docket, go to the Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street SW, room PL-401, Nassif Building, Washington, DC. To review copies of the service information, go to the National Archives and Records Administration (NARA). For information on the availability of this material at the NARA, call (202) 741-6030, or go to http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.

Issued in Renton, Washington, on September 2, 2005. Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.

References

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