E7-13116. Airworthiness Directives; Boeing Model 737-600, -700, -700C -800, and -900 Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), Department of Transportation (DOT).

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. This proposed AD would require revising the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness by incorporating new limitations for fuel tank systems to satisfy Special Federal Aviation Regulation No. 88 requirements. This proposed AD would also require the initial inspection of a certain repetitive AWL inspection to phase in that inspection, and repair if necessary. This proposed AD results from a design review of the fuel tank systems. We are proposing this AD to prevent the potential for ignition sources inside fuel tanks caused by latent failures, alterations, repairs, or maintenance actions, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.

DATES:

We must receive comments on this proposed AD by August 20, 2007.

ADDRESSES:

Use one of the following addresses to submit comments on this proposed AD.

• DOT Docket Web site: Go to http://dms.dot.gov and follow the instructions for sending your comments electronically.
• Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your comments electronically.
• Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.
• Fax: [phone].
• Hand Delivery: Room W12-140 on the ground floor of the West Building, 1200 New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207, for the service information identified in this proposed AD.

FOR FURTHER INFORMATION CONTACT:

Kathrine Rask, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind Ave SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to submit any relevant written data, views, or arguments regarding this proposed AD. Send your comments to an address listed in the ADDRESSES section. Include the docket number “FAA-2007-28384; Directorate Identifier 2006-NM-165-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments received by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://dms.dot.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed AD. Using the search function of that Web site, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov.

Examining the Docket

You may examine the AD docket on the Internet at http://dms.dot.gov, or in person at the Docket Operations office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Operations office (telephone [phone]) is located on the ground floor of the West Building at the DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the Docket Management System receives them.

Discussion

The FAA has examined the underlying safety issues involved in fuel tank explosions on several large transport airplanes, including the adequacy of existing regulations, the service history of airplanes subject to those regulations, and existing maintenance practices for fuel tank systems. As a result of those findings, we issued a regulation titled “Transport Airplane Fuel Tank System Design Review, Flammability Reduction and Maintenance and Inspection Requirements” (67 FR 23086, May 7, 2001). In addition to new airworthiness standards for transport airplanes and new maintenance requirements, this rule included Special Federal Aviation Regulation No. 88 (“SFAR 88,” Amendment 21-78, and subsequent Amendments 21-82 and 21-83).

Among other actions, SFAR 88 requires certain type design (i.e., type certificate (TC) and supplemental type certificate (STC)) holders to substantiate that their fuel tank systems can prevent ignition sources in the fuel tanks. This requirement applies to type design holders for large turbine-powered transport airplanes and for subsequent modifications to those airplanes. It requires them to perform design reviews and to develop design changes and maintenance procedures if their designs do not meet the new fuel tank safety standards. As explained in the preamble to the rule, we intended to adopt airworthiness directives to mandate any changes found necessary to address unsafe conditions identified as a result of these reviews.

In evaluating these design reviews, we have established four criteria intended to define the unsafe conditions associated with fuel tank systems that require corrective actions. The percentage of operating time during which fuel tanks are exposed to flammable conditions is one of these criteria. The other three criteria address the failure types under evaluation: Single failures, single failures in combination with another latent condition(s), and in-service failure experience. For all four criteria, the evaluations included consideration of previous actions taken that may mitigate the need for further action.

We have determined that the actions identified in this proposed AD are necessary to reduce the potential of ignition sources inside fuel tanks, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.

Relevant Service Information

We have reviewed the following subsections of Boeing 737-600/700/700C/700IGW/800/900 Maintenance Planning Data (MPD) Document, D626A001-CMR, Section 9, Revision March 2006 (hereafter referred to as “Revision March 2006 of the MPD”):

• Subsection D, “AIRWORTHINESS LIMITATIONS—SYSTEMS”
• Subsection E, “PAGE FORMAT: SYSTEM AIRWORTHINESS LIMITATIONS”
• Subsection F, “AIRWORTHINESS LIMITATIONS—FUEL SYSTEM AWLs”

Those subsections of Revision March 2006 of the MPD describe new airworthiness limitations (AWLs) for fuel tank systems. The new AWLs include:

• AWL inspections, which are periodic inspections of certain features for latent failures that could contribute to an ignition source; and
• Critical design configuration control limitations (CDCCLs), which are limitation requirements to preserve a critical ignition source prevention feature of the fuel tank system design that is necessary to prevent the occurrence of an unsafe condition. The purpose of a CDCCL is to provide instruction to retain the critical ignition source prevention feature during configuration change that may be caused by alterations, repairs, or maintenance actions. A CDCCL is not a periodic inspection.

Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition.

FAA's Determination and Requirements of the Proposed AD

We have evaluated all pertinent information and identified an unsafe condition that is likely to exist or develop on other airplanes of this same type design. For this reason, we are proposing this AD, which would require revising the AWLs section of the Instructions for Continued Airworthiness by incorporating the information in Subsections D, E, and F of Revision March 2006 of the MPD. This proposed AD would also require the initial inspection of a certain repetitive AWL inspection to phase in that inspection, and repair if necessary.

Explanation of Compliance Time

In most ADs, we adopt a compliance time allowing a specified amount of time after the AD's effective date. In this case, however, the FAA has already issued regulations that require operators to revise their maintenance/inspection programs to address fuel tank safety issues. The compliance date for these regulations is December 16, 2008. To provide for efficient and coordinated implementation of these regulations and this proposed AD, we are using this same compliance date in this proposed AD, instead of the 18-month compliance time recommended by Boeing.

Rework Required When Implementing AWLs Into an Existing Fleet

The AWLs revision for the fuel tank systems specified in paragraph (g) of this proposed AD, which involves incorporating the information specified in Revision March 2006 of the MPD, would affect how operators maintain their airplanes. After doing that AWLs revision, operators would need to do any maintenance on the fuel tank system as specified in the CDCCLs. Maintenance done before the AWLs revision specified in paragraph (g) would not need to be redone in order to comply with paragraph (g). For example, the AWL that requires fuel pumps to be repaired and overhauled per an FAA-approved component maintenance manual (CMM) applies to fuel pumps repaired after the AWLs are revised; spare or on-wing fuel pumps do not need to be reworked. For AWLs that require repetitive inspections, the initial inspection interval (threshold) starts from the date the AWL revision specified in paragraph (g) is done, except as provided by paragraph (h) of this proposed AD. This proposed AD would require only the AWLs revision specified in paragraph (g), and initial inspections specified in paragraph (h). No other fleet-wide inspections need to be done.

Changes to Fuel Tank System AWLs

Paragraph (g) of this proposed AD would require revising the AWLs section of the Instructions for Continued Airworthiness by incorporating certain information specified in Revision March 2006 of the MPD into the MPD. Paragraph (g) allows accomplishing the AWL revision in accordance with later revisions of the MPD as an acceptable method of compliance if they are approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA. Paragraph (h) allows accomplishing the initial inspections and repair in accordance with later revisions of the MPD as an acceptable method of compliance if they are approved by the Manager, Seattle ACO. In addition, Subsection D of Revision March 2006 of the MPD specifies that any deviations from the published AWL instructions, including AWL intervals, in that MPD must be approved by the Manager, Seattle ACO. Therefore, after the AWLs revision, any further revision to an AWL or AWL interval should be done as an AWL change, not as an alternative method of compliance (AMOC). For U.S.-registered airplanes, operators must make requests through an appropriate FAA Principal Maintenance Inspector (PMI) or Principal Avionics Inspector (PAI) for approval by the Manager, Seattle ACO. A non-U.S. operator should coordinate changes with its governing regulatory agency.

Exceptional Short-Term Extensions

Subsection D of Revision March 2006 of the MPD has provisions for an exceptional short-term extension of 30 days. An exceptional short-term extension is an increase in an AWL interval that may be needed to cover an uncontrollable or unexpected situation. For U.S.-registered airplanes, the FAA PMI or PAI must concur with any exceptional short-term extension before it is used, unless the operator has identified another appropriate procedure with the local regulatory authority. The FAA PMI or PAI may grant the exceptional short-term extensions described in Subsection D without consultation with the Manager, Seattle ACO. A non-U.S. operator should coordinate changes with its governing regulatory agency. As explained in Revision March 2006 of the MPD, exceptional short-term extensions must not be used for fleet AWL extensions. An exceptional short-term extension should not be confused with an operator's short-term escalation authorization approved in accordance with the Operations Specifications or the operator's reliability program.

Ensuring Compliance With Fuel Tank System AWLs

Boeing has revised applicable maintenance manuals and task cards to address AWLs and to include notes about CDCCLs. Operators that do not use Boeing's revision service should revise their maintenance manuals and task cards to highlight actions tied to CDCCLs to ensure that maintenance personnel are complying with the CDCCLs. Appendix 1 of this proposed AD contains a list of Air Transport Association (ATA) sections for the revised maintenance manuals. Operators might wish to use the appendix as an aid to implement the AWLs.

Recording Compliance With Fuel Tank System AWLs

The applicable operating rules of the Federal Aviation Regulations (14 CFR parts 91, 121, 125, and 129) require operators to maintain records with the identification of the current inspection status of an airplane. Some of the AWLs contained in Subsection F of Revision March 2006 of the MPD are inspections for which the applicable sections of the operating rules apply. Other AWLs are CDCCLs, which are tied to conditional maintenance actions. An entry into an operator's existing maintenance record system for corrective action is sufficient for recording compliance with CDCCLs, as long as the applicable maintenance manual and task cards identify actions that are CDCCLs.

Changes to CMMs Cited in Fuel Tank System AWLs

Some of the AWLs in Subsection F of Revision March 2006 of the MPD refer to specific revision levels of the CMMs as additional sources of service information for doing the AWLs. Boeing is referring to the CMMs by revision level in the applicable AWL for certain components rather than including information directly in the MPD because of the volume of that information. As a result, the Manager, Seattle ACO, must approve the CMMs. Any later revision of those CMMs will be handled like a change to the AWL itself. Any use of parts (including the use of parts manufacturer approval (PMA) approved parts), methods, techniques, and practices not contained in the CMMs need to be approved by the Manager, Seattle ACO, or governing regulatory authority. For example, certain pump repair/overhaul manuals must be approved by the Manager, Seattle ACO.

Changes to AMMs Referenced in Fuel Tank System AWLs

In other AWLs in Subsection F of Revision March 2006 of the MPD, the AWLs contain all the necessary data. The applicable section of the maintenance manual is usually included in the AWLs. Boeing intended this information to assist operators in maintaining the maintenance manuals. A maintenance manual change to these tasks may be made without approval by the Manager, Seattle ACO, through an appropriate FAA PMI or PAI, by the governing regulatory authority, or by using the operator's standard process for revising maintenance manuals. An acceptable change would have to maintain the information specified in the AWL such as the pass/fail criteria or special test equipment.

Costs of Compliance

There are about 1960 airplanes of the affected design in the worldwide fleet. The following table provides the estimated costs, at an average labor rate of $80 per hour, for U.S. operators to comply with this proposed AD.

Estimated Costs

Action	Work hours	Parts	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
AWLs revision	8	None	$640	682	$436,480
Inspection	8	None	640	682	436,480

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 proposed AD would not have federalism implications under Executive Order 13132. This proposed AD 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.

For the reasons discussed above, I certify that the 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. 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 proposed AD and placed it in the AD docket. 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
• Safety

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 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. The Federal Aviation Administration (FAA) amends § 39.13 by adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2007-28384; Directorate Identifier 2006-NM-165-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by August 20, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 737-600, -700, -700C -800, and -900 series airplanes, certificated in any category, with an original standard airworthiness certificate or original export certificate of airworthiness issued before March 31, 2006.

Note 1:

Airplanes with an original standard airworthiness certificate or original export certificate of airworthiness issued on or after March 31, 2006, must already be in compliance with the airworthiness limitations specified in this AD because those limitations were applicable as part of the airworthiness certification of those airplanes.

Note 2:

This AD requires revisions to certain operator maintenance documents to include new inspections and maintenance actions. Compliance with these limitations is required by 14 CFR 43.16 and 91.403(c). For airplanes that have been previously modified, altered, or repaired in the areas addressed by these limitations, the operator may not be able to accomplish the actions described in the revisions. In this situation, to comply with 14 CFR 43.16 and 91.403(c), the operator must request approval for revision to the airworthiness limitations (AWLs) in the Boeing 737-600/700/700C/700IGW/800/900 Maintenance Planning Data (MPD) Document, D626A001-CMR, according to paragraph (g) or (i) of this AD, as applicable.

Unsafe Condition

(d) This AD results from a design review of the fuel tank systems. We are issuing this AD to prevent the potential for ignition sources inside fuel tanks caused by latent failures, alterations, repairs, or maintenance actions, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.

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.

Service Information Reference

(f) The term “Revision March 2006 of the MPD” as used in this AD, means Boeing 737-600/700/700C/700IGW/800/900 Maintenance Planning Data (MPD) Document, D626A001-CMR, Section 9, Revision March 2006.

Revision to AWLs Section

(g) Before December 16, 2008, revise the AWLs section of the Instructions for Continued Airworthiness by incorporating into the MPD the information in the subsections specified in paragraphs (g)(1), (g)(2), and (g)(3) of this AD; except that the initial inspection required by paragraph (h) of this AD must be done at the applicable compliance time specified in that paragraph. Accomplishing the revision in accordance with a later revision of the MPD is an acceptable method of compliance if the revision is approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA.

(1) Subsection D, “AIRWORTHINESS LIMITATIONS—SYSTEMS,” of Revision March 2006 of the MPD.

(2) Subsection E, “PAGE FORMAT: SYSTEM AIRWORTHINESS LIMITATIONS,” of Revision March 2006 of the MPD.

(3) Subsection F, “AIRWORTHINESS LIMITATIONS—FUEL SYSTEM AWLs,” of Revision March 2006 of the MPD.

Initial Inspection and Repair if Necessary

(h) At the later of the compliance times specified in paragraphs (h)(1) and (h)(2) of this AD, do a special detailed inspection of the lightning shield to ground termination on the out-of-tank fuel quantity indication system (FQIS) wiring to verify functional integrity, in accordance with AWL Number 28-AWL-03 of Subsection F of Revision March 2006 of the MPD. If any discrepancy is found during the inspection, repair the discrepancy before further flight in accordance with AWL Number 28-AWL-03 of Subsection F of Revision March 2006 of the MPD. Accomplishing the actions required by this paragraph in accordance with a later revision of the MPD is an acceptable method of compliance if the revision is approved by the Manager, Seattle ACO.

Note 3:

For the purposes of this AD, a special detailed inspection is: “An intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. The examination is likely to make extensive use of specialized inspection techniques and/or equipment. Intricate cleaning and substantial access or disassembly procedure may be required.”

(1) Prior to the accumulation of 36,000 total flight hours, or within 120 months since the date of issuance of the original standard airworthiness certification or the date of issuance of the original export certificate of airworthiness, whichever occurs first.

(2) Within 24 months after the effective date of this AD.

Alternative Methods of Compliance (AMOCs)

(i)(1) The Manager, Seattle ACO, has the authority to approve AMOCs for this AD, if requested in accordance with the procedures found in 14 CFR 39.19.

(2) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Before using any approved AMOC on any airplane to which the AMOC applies, notify your appropriate principal inspector (PI) in the FAA Flight Standards District Office (FSDO), or lacking a PI, your local FSDO.

Appendix 1.—Implementing Fuel Tank System Airworthiness Limitations on Model 737-600, -700, -700C -800, and -900 Series Airplanes

AWL No.	ALI/CDCCL	ATA section or CMM document	Task title	Task No.
28-AWL-01	ALI	AMM 28-11-00/601	External Wires Over the Center Fuel Tank Inspection	28-11-00-211-801.
28-AWL-02	CDCCL	SWPM 20-10-11	Wiring Assembly and Installation Configuration.
28-AWL-03	ALI	AMM 05-55-54/601	FQIS Wiring and Bonding—Inspection	05-55-54-200-801.
28-AWL-04	CDCCL	SWPM 20-10-15	Assembly of Shield Ground Wires.
28-AWL-05	CDCCL	SWPM 20-10-11	Wiring Assembly and Installation Configuration.
28-AWL-06	CDCCL	CMM 28-41-87, Revision 1, or subsequent revisions.
28-AWL-07	CDCCL	AMM 28-41-24/401	Densitometer Hot Short Protector—Installation	28-41-24-400-801.
28-AWL-08	CDCCL	CMM 28-41-76, Revision 1; CMM 28-41-75, Revision 0; CMM 28-40-59, Revision E; CMM 28-41-62, Revision 1; CMM 28-41-63, Revision 1; or subsequent revisions.
28-AWL-09	CDCCL	SWPM 20-14-12	Repair of Fuel Quantity Indicator System (FQIS) Wire Harness.
		AMM 28-41-44/401	FQIS Wire Harness Replacement	28-41-44-400-801.
		AMM 28-41-42/401	FQIS Spar Penetration Connector—Installation	28-41-42-420-801.
28-AWL-10	CDCCL	AMM 29-11-04/401	Heat Exchanger Installation	29-11-04-400-801.
28-AWL-11	CDCCL	AMM 28-22-15/401	Fuel Line, Fitting, and Coupling Installation	28-22-15-400-801.
28-AWL-12	CDCCL
28-AWL-13	CDCCL	CMM 28-22-08, Revision 0; CMM 28-22-09, Revision 2; CMM 28-20-02, Revision 9; or subsequent revisions.
28-AWL-14	CDCCL	AMM 28-22-41/401	Install the Motor Impeller	28-22-41-400-801.
28-AWL-15	CDCCL	AMM 28-21-71/401	Float Switch Installation	28-21-71-400-802.
			Float Switch Removal	28-21-71-020-801.
28-AWL-16	CDCCL	AMM 28-11-11/401	Main Tank Access Door Installation Surge Tank Access Door—Installation	28-11-11-400-801. 28-11-11-400-802.
		AMM 28-11-31/401	Center Tank Access Door—Installation	28-11-31-400-801.
28-AWL-17	CDCCL	AMM 28-13-41/401	Relief Valve Installation	28-13-41-400-801.
		AMM 28-13-31/401	Flame Arrestor Installation	28-13-31-400-801.
28-AWL-18	CDCCL	FIM 28-22-00/201	No. 1 Tank, Forward Boost Pump Circuit Breaker Open—Fault Isolation	28-22 Task 813.
			No. 1 Tank, Aft Boost Pump Circuit Breaker Open—Fault Isolation	28-22 Task 814.
			No. 2 Tank, Forward Boost Pump Circuit Breaker Open—Fault Isolation	28-22 Task 815.
			No. 2 Tank, Aft Boost Pump Circuit Breaker Open—Fault Isolation	28-22 Task 816.
			Center Tank, Left Boost Pump Circuit Breaker Open—Fault Isolation	28-22 Task 817.
			Center Tank, Right Boost Pump Circuit Breaker Open—Fault Isolation	28-22 Task 818.
28-AWL-19	ALI	AMM 28-22-00/501	Center Tank Boost Pump Auto Shutoff Functional Test	28-22-00-720-805.
28-AWL-20
28-AWL-21	CDCCL	AMM 28-22-11/401	Install the Actuator of the Spar Valve	28-22-11-400-804.
			Install the Valve Adapter of the Spar Valve	28-22-11-400-805.
		AMM 28-22-21/401	Install the Actuator of the Engine Fuel Crossfeed Valve	28-22-21-400-804.
			Install the Engine Fuel Crossfeed Valve Adapter	28-22-21-400-805.
28-AWL-22	CDCCL	CMM 28-20-21

Issued in Renton, Washington, on June 22, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.