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 installation of an automatic shutoff system for the center tank fuel boost pumps, installation of a placard in the airplane flight deck if necessary, and concurrent modification of the P5-2 fuel control module assembly. This proposed AD would also require revisions to the Limitations and Normal Procedures sections of the airplane flight manual to advise the flightcrew of certain operating restrictions for airplanes equipped with an automated center tank fuel pump shutoff control. This proposed AD would also require a revision to the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness to incorporate AWL No. 28-AWL-19 and No. 28-AWL-23. This proposed AD would also require installation of two secondary override fuel pump control relays to each existing primary override fuel pump control relay for the center fuel tank fuel boost pumps. This proposed AD results from fuel system reviews conducted by the manufacturer. We are proposing this AD to prevent center tank fuel pump operation with continuous low pressure, which could lead to friction sparks or overheating in the fuel pump inlet or could create a potential ignition source inside the center fuel tank; these conditions, in combination with flammable fuel vapors, could result in a center fuel tank explosion and consequent loss of the airplane.

DATES:

We must receive comments on this proposed AD by August 24, 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: (202) 493-2251.
• 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 (425) 917-6505; fax (425) 917-6590.

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-2007-28661; Directorate Identifier 2007-NM-013-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 (800) 647-5527) 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” (66 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 a 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 fuel tank explosions and consequent loss of the airplane.

Boeing has found that certain failures will result in the center tank fuel pumps continuing to run after the tank has been depleted. Depending on the failure, pump low pressure may not be annunciated, or power may not be removed from the pump when the pump has been commanded “OFF.” Operation of the center tank fuel pump with continuous low pressure could lead to friction sparks or overheating in the fuel boost pump inlet. This condition, if not corrected, could result in a fuel tank explosion and consequent loss of the airplane.

Other Relevant Rulemaking

On April 18, 2001, we issued AD 2001-08-24, amendment 39-12201 (66 FR 20733, April 25, 2001), applicable to all Boeing Model 737 airplanes. That AD requires revising the airplane flight manual (AFM) to prohibit extended dry operation of the center tank fuel pumps (with no fuel passing through the pumps). Accomplishing the actions specified in paragraphs (g), (h), (i), (j), and (k) of this proposed AD would terminate the AFM revision required by paragraph (a) of AD 2001-08-24 for Model 737-600, -700, -700C, -800, and -900 series airplanes that have the automatic shutoff system installed.

On September 24, 2002, we issued AD 2002-19-52, amendment 39-12900 (67 FR 61253, September 30, 2002), applicable to all Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes, Model 747 airplanes, and Model 757 airplanes. That AD requires revising the AFM to advise the flightcrew of certain operating restrictions for maintaining minimum fuel levels, prohibits use of the horizontal stabilizer tank on certain airplanes, and prohibits the installation of certain fuel pumps. That AD requires concurrent removal of the currently required AFM revisions and insertion of new AFM revisions, requires installation of placards to alert the flightcrew to the operating restrictions, and prohibits installation of any un-inspected pumps. That AD permits the AFM revision and placard to be removed under certain conditions. Installation of a placard in accordance with paragraph (e) of AD 2002-19-52, amendment 39-12900, is acceptable for compliance with paragraph (h) of this AD.

On November 23, 2002, we issued emergency AD 2002-24-51, amendment 39-12992, applicable to all Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes, Model 747 airplanes, and Model 757 airplanes. (We issued a Federal Register version of AD 2002-24-51 on December 23, 2002 (68 FR 10, January 2, 2003).) That AD requires revising the AFM to require the flightcrew to maintain certain minimum fuel levels in the center fuel tanks and, for certain airplanes, to prohibit the use of the horizontal stabilizer fuel tank and certain center auxiliary fuel tanks. Accomplishing the actions specified in paragraphs (g), (h), (i), (j), and (k) of this proposed AD would terminate the AFM revision specified in paragraph (b) of AD 2002-24-51 for Model 737-600, -700, -700C, -800, and -900 series airplanes that have the automatic shutoff system installed.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-28A1206, dated January 11, 2006. This service bulletin describes procedures for installing an automatic shutoff system for the center tank fuel boost pumps. Installation of the automatic shutoff system includes the following actions:

• In the J4 junction box, changing wiring and connector termination positions and installing relays, transformers, markers, and wires to a certain wire bundle.
• In the J20 junction box, changing wiring and installing relays, markers, and wires to a certain wire bundle.
• At the P5 overhead panel in the flight compartment, replacing the P5-2 fuel control module with a reworked P5-2 fuel control module.
• In the flight compartment, installing the P61-8 fuel test panel and installing circuit breakers and markers in the P6-3 circuit breaker panel.
• Adding wiring to certain wire bundles in the P6 circuit breaker panel, between the flight and electronics compartment, in the J4 and J20 junction boxes, in the E2-1 and E4-2 electronics shelves in the electrical compartment, between the E2-1 electronics shelf and the P5-2 fuel control panel, between the E4-2 electronics shelf and the P5-2 fuel control panel, between the E2-1 electronics shelf and the J20 junction box, and between the E4-2 electronics shelf and the J4 junction box.

We have also reviewed Boeing Alert Service Bulletin 737-28A1248, dated December 21, 2006. This service bulletin describes procedures for installing two secondary override fuel pump control relays to each existing primary override fuel pump control relay for the center fuel tank fuel boost pumps. The installation includes installing a new overlay marker and Brady label, changing and adding certain wires, and connecting the new relays to the power distribution panel.

We have also reviewed Revision December 2005 and Revision May 2006 of Section 9 of the Boeing 737-600/700/700C/700IGW/800/900 Maintenance Planning Data (MPD) Document, D626A001-CMR (hereafter referred to as “the MPD”). Subsection F, “AIRWORTHINESS LIMITATIONS—FUEL SYSTEM AWLs,” of the MPD describes new airworthiness limitations (AWLs) for fuel tank systems. The AWLs include:

• AWL inspections, which are periodic inspections of certain features for latent failures that could contribute to an ignition source.
• 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.

Subsection F of the MPD, Revision December 2005, adds new fuel system AWL No. 28-AWL-19, which is a repetitive inspection of the automatic shutoff system for the center tank fuel boost pumps to verify functional integrity. Subsection F of the MPD, Revision May 2006, adds new fuel system AWL No. 28-AWL-23, which is a repetitive inspection of the power failed on protection system for the center tank fuel boost pumps to verify functional integrity.

Boeing Alert Service Bulletin 737-28A1206 recommends concurrent accomplishment of Boeing Component Service Bulletin 233A3202-28-03, dated January 12, 2006. Boeing Component Service Bulletin 233A3202-28-03 describes procedures for replacing the left and right center boost pump switches of the P5-2 fuel control module assembly with new switches and changing the wiring of the P5-2 fuel control module assembly.

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 the following actions:

• Installation of an automatic shutoff system for the center tank fuel boost pumps.
• Installation of a placard in the airplane flight deck, if necessary. (Placards are necessary only for “mixed fleet operation,” which means that some airplanes in an operator's fleet are equipped with automatic shutoff systems while other airplanes are not.)
• Concurrent modification of the P5-2 fuel control module assembly.
• Revisions to the Limitations and Normal Procedures sections of the AFM to advise the flightcrew of certain operating restrictions for airplanes equipped with an automated center tank fuel pump shutoff control.
• Revision to the AWLs section of the Instructions for Continued Airworthiness to incorporate AWL No. 28-AWL-19, which would require repetitive inspections of the automatic shutoff system for the center tank fuel boost pumps to verify functional integrity.
• Installation of two secondary override fuel pump control relays to each existing primary override fuel pump control relay for the center fuel tank fuel boost pumps.
• Revision to the AWLs section of the Instructions for Continued Airworthiness to incorporate AWL No. 28-AWL-23, which would require repetitive inspections of the power failed on protection system for the center tank fuel boost pumps to verify functional integrity.

This proposed AD would also allow accomplishing the revision to the AWLs section of the Instructions for Continued Airworthiness 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.

Costs of Compliance

There are about 2,109 airplanes of the affected design in the worldwide fleet. The following table provides the estimated costs, at an average labor rate of $80 per work hour, for U.S. operators to comply with this proposed AD. The estimated cost of parts for installing an automatic shutoff system depends on the configuration of an airplane.

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.