E7-20049. Airworthiness Directives; McDonnell Douglas Model 717-200 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 McDonnell Douglas Model 717-200 airplanes. This proposed AD would require modification of the conduit for the forward boost pump of the center fuel tank. This proposed AD results from the finding that a potential chafing condition exists in the volute assembly of the forward boost pump for the center fuel tank. We are proposing this AD to prevent chafing of the forward boost pump wiring that could lead to arcing to the inside of the 45-degree angle fitting, 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 November 26, 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.
• Governmentwide 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, Long Beach Division, 3855 Lakewood Boulevard, Long Beach, California 90846, Attention: Data and Service Management, Dept. C1-L5A (D800-0024), for the service information identified in this proposed AD.

FOR FURTHER INFORMATION CONTACT:

Samuel S. Lee, Aerospace Engineer, Propulsion Branch, ANM-140L, FAA, Los Angeles Aircraft Certification Office, 3960 Paramount Boulevard, Lakewood, California 90712-4137; 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-2007-29329; Directorate Identifier 2007-NM-205-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 level 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.

We have received a report indicating that a potential chafing condition exists in the volute assembly of the forward boost pump for the center fuel tank, on McDonnell Douglas Model 717-200 airplanes. Boeing discovered this condition during an investigation of the wiring installations for the fuel boost pump. The wiring that provides electrical power to the forward boost pump for the center fuel tank is installed in a flexible conduit inside the right wing fuel tank and is routed to the volute assembly. The potential chafing area exists at the 45-degree angle fitting (made of anodized aluminum) of the volute assembly. This angle fitting has been found to have an internal uncontrolled edge that could cause damage to the wiring insulation. Chafed wiring could lead to arcing to the inside of the 45-degree angle fitting. This condition, if not corrected, 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 Boeing Service Bulletin 717-28-0007, Revision 1, dated September 23, 2003. The service bulletin describes procedures for modifying the conduit for the forward boost pump of the center fuel tank. The modification includes removing conduit from the 45-degree angle fitting of the forward boost pump and routing the conduit to the existing straight fitting in the bottom of the pump volute located in the right wing fuel tank. 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 accomplishing the actions specified in the service information described previously, except as discussed under “Difference between the Proposed AD and Service Bulletin.”

Difference Between the Proposed AD and Service Bulletin

Although the service bulletin recommends accomplishing the modification at “a scheduled maintenance period when manpower, materials, and facilities are available,” we have determined that this compliance time is imprecise and would not address the identified unsafe condition in a timely manner. In developing an appropriate compliance time for this AD, we considered not only the manufacturer's recommendation, but the degree of urgency associated with addressing the subject unsafe condition, the average utilization of the affected fleet, and the time necessary to perform the modification. In light of all of these factors, we find a compliance time of 78 months for completing the required actions to be warranted, in that it represents an appropriate interval of time for affected airplanes to continue to operate without compromising safety. We have coordinated this difference with Boeing.

Costs of Compliance

There are about 77 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 61 airplanes of U.S. registry. The proposed actions would take about 9 work hours per airplane, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the proposed AD for U.S. operators is $43,920, or $720 per 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.

§ 39.13

[Amended]

2. The Federal Aviation Administration (FAA) amends § 39.13 by adding the following new airworthiness directive (AD):

McDonnell Douglas: Docket No. FAA-2007-29329; Directorate Identifier 2007-NM-205-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by November 26, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to McDonnell Douglas Model 717-200 airplanes, certificated in any category; as identified in Boeing Service Bulletin 717-28-0007, Revision 1, dated September 23, 2003.

Unsafe Condition

(d) This AD results from a finding that a potential chafing condition exists in the volute assembly of the forward boost pump for the center fuel tank. We are issuing this AD to prevent chafing of the forward boost pump wiring that could lead to arcing to the inside of the 45-degree angle fitting, 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.

Modification

(f) Within 78 months after the effective date of this AD, modify the conduit for the forward boost pump of the center fuel tank, by accomplishing all of the actions specified in the Accomplishment Instructions of Boeing Service Bulletin 717-28-0007, Revision 1, dated September 23, 2003.

Alternative Methods of Compliance (AMOCs)

(g)(1) The Manager, Los Angeles Aircraft Certification Office (ACO), FAA, 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.

Issued in Renton, Washington, on October 1, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.