Airworthiness Directives; Boeing Model 747-400, 777-200, and 777-300 Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Supplemental notice of proposed rulemaking; reopening of comment period.

SUMMARY:

This document revises an earlier proposed airworthiness directive (AD), applicable to certain Boeing Model 747-400, 777-200, and 777-300 series airplanes, that would have required, for certain airplanes, replacement of the cell stack of the flight deck humidifier with a supplier-tested cell stack, or replacement with an end plate and subsequent deactivation of the flight deck humidifier. For other airplanes, that proposed AD would have required replacement of the cell stack with a blanking plate or a new cell stack, or replacement of the blanking plate with a supplier-tested cell stack. This new action revises the proposed AD by adding airplanes to the applicability; adding new inspections to determine certain part numbers; requiring replacement of the blanking plate with a supplier-tested cell stack if necessary; and changing certain words to clarify the intent of the proposed AD. The actions specified by this new proposed AD are intended to prevent an increased pressure drop across the humidifier and consequent reduced airflow to the flight deck, which could result in the inability to clear any smoke that might appear in the flight deck. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by January 31, 2005.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-360-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 p.m., Monday through Friday, except Federal holidays. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2000-NM-360-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 or 2000 or ASCII text.

The service information referenced in the proposed rule may be obtained from Boeing Commercial Airplanes, PO Box 3707, Seattle, Washington 98124-2207. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT:

Jeffrey S. Palmer, Aerospace Engineer, Cabin Safety and Environmental Systems Branch, ANM-150S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 917-6481; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Communications shall 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, specified above, will be considered before taking action on the proposed rule. The proposals contained in this action may be changed in light of the comments received.

Submit comments using the following format:

• Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
• For each issue, state what specific change to the proposed AD is being requested.
• Include justification (e.g., reasons or data) for each request.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed 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 summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NM-360-AD.” The postcard will be date stamped and returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-360-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to add an airworthiness directive (AD), applicable to certain Boeing Model 747-400, 777-200, and 777-300 series airplanes, was published as a notice of proposed rulemaking (NPRM) (hereafter referred to as the “original NPRM”) in the Federal Register on September 19, 2003 (68 FR 54874). The original NPRM would have required, for certain airplanes, replacement of the cell stack of the flight deck humidifier with a supplier-tested cell stack, or replacement with an end plate and subsequent deactivation of the flight deck humidifier. The original NPRM also would have required, for other airplanes, replacement of the cell stack with a blanking plate or a new cell stack, or replacement of the blanking plate with a supplier-tested cell stack. The original NPRM was prompted by reports of sagging cell stack membranes of the flight deck humidifiers. That condition, if not corrected, could result in the inability to clear any smoke that might appear in the flight deck.

Comments

Due consideration has been given to the comments received in response to the original NPRM. Some of the comments, as discussed below, have resulted in changes to the original NPRM.

Request To Withdraw the Proposed AD

One commenter, the parts manufacturer, requests that the proposed AD be withdrawn. The commenter contends that all affected humidifiers have been screened for the suspect cell stacks. The commenter also notes that it had no ability to track some of the cell stack serial numbers.

The FAA does not agree to withdraw the proposed AD. We have not received confirmation that all Model 747-400, 777-200, 777-300 series airplanes equipped with Hamilton Sundstrand flight deck humidifiers have been screened for the suspect cell stacks. Even if the airplanes specified in Boeing Alert Service Bulletin 747-21-A2414, Revision 1, dated October 26, 2000, and Boeing Service Bulletin 777-21A0048, Revision 1, dated September 7, 2000 (referenced as the appropriate sources of service information for accomplishing the proposed actions), were verified not to have a defective cell stack, a defective cell stack could have been installed on certain other airplanes with a Hamilton Sundstrand humidifier. If an airplane not listed in the service bulletin was originally delivered with an acceptable cell stack, it is possible that, through maintenance or replacement actions, a defective cell stack could have been installed on any Model 747-400, 777-200, or 777-300 airplane with a Hamilton Sundstrand humidifier having part number (P/N) 821486-1 or P/N 816086-1.

Based on further review, we have determined that there were approximately 100 flight deck humidifiers produced with the defective cell stack and that 114 airplanes could be fitted with the defective cell stack.

Due to the possibility that a defective cell stack could have been installed on any Model 747-400, 777-200, or 777-300 series airplane equipped with a Hamilton Sundstrand humidifier having P/N 821486-1 or P/N 816086-1, we have added an inspection of Model 747-400, 777-200, and 777-300 series airplanes equipped with Hamilton Sundstrand flight deck humidifiers to determine if P/N 821486-1 or P/N 816086-1 is installed, and as applicable, an inspection to determine if the cell stack has P/N 821482-1 or P/N 822976-2. We have added inspections or records reviews to paragraphs (a) and (d) of the supplemental NPRM and revised the other paragraphs accordingly.

The applicability of the supplemental NPRM has also been revised to “Model 747-400, 777-200, 777-300 series airplanes, equipped with Hamilton Sundstrand flight deck humidifiers.” In addition, the cost table has been revised to include the cost of the additional inspections and we have revised the number of affected airplanes to 114 worldwide and 29 of U.S. registry.

Request To Revise Number of Affected Airplanes of U.S. Registry

One commenter, the airplane manufacturer, requests that the number of airplanes of U.S. registry be revised from 12 to none. The commenter notes that the original NPRM specifies there are “35 airplanes of the affected design in the worldwide fleet. The FAA estimates that 12 airplanes of U.S. registry would be affected by this AD.” The commenter states that it has delivered 103 airplanes in production that could be fitted with the cell stack with excessive pressure drop (although only 23 may have been delivered in that configuration). The commenter notes that only one domestic operator has airplanes equipped with Hamilton Sundstrand humidifiers and that this operator cannot have any Model 777 series airplanes having cell stacks with excessive pressure drop. The commenter states the first Model 777 series airplane equipped with a Hamilton Sundstrand humidifier for this operator was the airplane on which the pressure drop discrepancy was discovered, and it was outfitted with a humidifier with an acceptable pressure drop. The commenter goes on to state that this operator's flight deck humidifier stock is known, and it can be shown that no affected cell stacks exist within that operator's fleet. Consequently, the commenter believes no airplanes of U.S. registry would be affected by this proposed AD.

We do not agree with the commenter's request to revise the number of airplanes of U.S. registry from 12 to none. As stated in the previous paragraph “Request to Withdraw the Proposed AD,” there is a possibility that a defective cell stack could have been installed on any Model 747-400, 777-200, or 777-300 series airplane equipped with a Hamilton Sundstrand humidifier having P/N 821486-1 or P/N 816086-1. Because we have not received confirmation that all Model 747-400, 777-200, 777-300 series airplanes equipped with Hamilton Sundstrand flight deck humidifiers have been screened for the suspect cell stacks, the applicability of the supplemental NPRM has been revised and the number of airplanes of U.S. registry has been revised to 29.

Request To Remove “Replacement of the Blanking Plate With a Supplier Tested Cell Stack” Text From Summary and Cost Table

One commenter, the airplane manufacturer, requests that in the Summary of the original NPRM, the text “or replacement of the blanking plate with a supplier tested cell stack” be removed and the final row of the cost table in the Cost Impact section be removed. The commenter notes that to mitigate the risk of reduced flight deck airflow the original NPRM requires “For other airplanes, replacement of the cell stack with a blanking plate or a new cell stack, or replacement of the blanking plate with a supplier-tested cell stack.” The commenter states that a risk of reduced airflow to the flight deck does not exist when a blanking plate is installed.

We agree that if a blanking plate is installed, reduced airflow to the flight deck will not occur. However, the text “or replacement of the blanking plate with a supplier-tested cell stack” is intended to prevent a discrepant part from being installed on an airplane on which an installed blanking plate is removed and a cell stack is installed. Therefore, in the summary of the supplemental NPRM, for the reasons we are revising the proposed AD, we have added the text “requiring replacement of the blanking plate with a supplier-tested cell stack if necessary” in order to clarify the intent of the proposed AD. We have not changed the cost table.

Request To Clarify Referenced Requirements

The same commenter states that it is unclear which four requirements of paragraph (a)(1) of the original NPRM are being referenced in paragraph (a)(2) of the original NPRM that states “Replacement of the cell stack with a supplier-tested cell stack in accordance with the 4 requirements of paragraph (a)(1) of this AD * * *”

We agree that paragraph (b)(2) (specified as paragraph (a)(2) of the original NPRM) should be clarified. The “4” in the “Replacement of the cell stack * * *” sentence was a typographical error. The sentence also should have specified that it was a replacement of the “end plate” and not the “cell stack.” The intent of the sentence was to indicate that the humidifier could be reactivated if the end plate was replaced with a supplier-tested cell stack. In addition, the sentence references Part 1 of Boeing Alert Service Bulletin 747-21A2414, Revision 1, dated October 26, 2000, as the relevant source of service information for the replacement. However, Part 1 of the service bulletin does not include procedures for the replacement of the end plate. The replacement of the end plate must be done in a method approved by the FAA. We have revised paragraphs (b) and (b)(2) of the supplemental NPRM and added paragraph (b)(3) of the supplemental NPRM to clarify that there is an option to replace the end plate with a supplier-tested cell stack.

Request To Remove Paragraph (c)(3) of the Original NPRM

The same commenter also requests removing paragraph (c)(3) of the original NPRM. The commenter states that paragraph (c)(3) concerns replacing a blanking plate with a cell stack. However, the commenter believes this is not necessary, as a humidifier with a blanking plate does not restrict flight deck airflow. The commenter states that this action is not necessary since the risk of reduced airflow to the flight deck does not exist when a blanking plate is installed.

We agree with the commenter that reduced airflow to the flight deck does not exist when a blanking plate is installed. However, the purpose of paragraph (e)(3) (specified as paragraph (c)(3) of the original NPRM) of the supplemental NPRM is to prevent a discrepant part from being installed on an airplane if the operator chooses to remove a blanking plate and install a cell stack in its place. Thus, while we do not agree to remove paragraph (e)(3) (specified as paragraph (c)(3) of the original NPRM) of the supplemental NPRM, we have revised the wording in paragraph (e)(3) of the supplemental NPRM to, “If a blanking plate is removed, and a cell stack installed, the cell stack installation must be done in accordance with Part 3 of the service bulletin.”

Request to Revise “Dehumidifier” to “Humidifier”

The same commenter requests the word “dehumidifier” be revised to “humidifier.” The commenter notes that paragraph (e) of the original NPRM specifies “flight deck dehumidifier cell stack.” The subject of the original NPRM is a humidifier cell stack.

We agree with the commenter. Paragraph (g) (specified as paragraph (e) of the original NPRM) of the supplemental NPRM has been revised to specify “flight deck humidifier cell stack.”

Request To Revise Reason Given for Sagging Cell Problem

The same commenter requests that the cause of the sagging cell problem be changed to “insufficient rigidity in the cell frame.” The commenter notes that the “Discussion” section of the original NPRM states, “The sagging has been attributed to difficulties encountered during the membrane welding process.” The commenter states that the sagging is actually a result of the cell frame material not being rigid. The action taken to correct the sagging cell problem is to change the cell frame material in order to make it more rigid.

We agree with the commenter that the sagging is actually a result of the cell frame material not being rigid. However, since the wording from the original NPRM “the sagging has been attributed to difficulties encountered during the membrane welding process” is not restated in the supplemental NPRM, no change is made.

Request To Clarify Reason for Increased Pressure

The same commenter requests that we clarify when there is an increased pressure drop across the humidifier. The commenter notes that the Discussion section of the original NPRM states “The result of the sagging membrane is an increased pressure drop across the humidifier (if it is activated).” The commenter states that the increased pressure drop would exist regardless of whether the humidifier is activated or not.

We agree that the increased pressure drop would exist regardless of whether the humidifier is activated or not. Boeing Alert Service Bulletins 747-21A2412 and 777-21A0048 do not state that the pressure drop occurs only when the humidifier is activated. However, since the Discussion section of the original NPRM is not restated in the supplemental NPRM, no change is made.

Conclusion

Since these changes expand the scope of the originally proposed rule, we have determined that it is necessary to reopen the comment period to provide additional opportunity for public comment.

Changes to Delegation Authority

Boeing has received a Delegation Option Authorization (DOA). We have revised this supplemental NPRM to delegate the authority to approve an alternative method of compliance for any repair required by this AD to the Authorized Representative for the Boeing DOA Organization rather than the Designated Engineering Representative (DER).

Cost Impact

There are approximately 114 airplanes of the affected design in the worldwide fleet. The FAA estimates that 29 airplanes of U.S. registry would be affected by this proposed AD. The following cost estimates would vary depending on the actions chosen by the operator.

The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this proposed AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

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 Impact

The regulations proposed herein would 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. Therefore, it is determined that this proposal would not have federalism implications under Executive Order 13132.

For the reasons discussed above, I certify that this proposed regulation (1) is not a “significant regulatory action” under Executive Order 12866; (2) is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated, 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 draft regulatory 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
• Safety

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend 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.