E9-314. Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 737-300, -400, and -500 series airplanes. This proposed AD would require modifying the control power wiring of the normal supply fan and the low flow sensor for the equipment cooling system of the electronic flight instrument system (EFIS). This proposed AD results from a report of loss of both the normal EFIS cooling supply and the indication of EFIS cooling loss due to a single failure of the battery bus, causing eventual power-down of the EFIS displays; the standby attitude indication is also powered by this battery bus. We are proposing this AD to prevent loss of all attitude indications from both the standby indicator and EFIS displays, which could decrease the ability of the flightcrew to maintain the safe flight and landing of the airplane.

DATES:

We must receive comments on this proposed AD by February 26, 2009.

ADDRESSES:

You may send comments by any of the following methods:

• Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
• Fax: [phone].
• 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.
• Hand Delivery: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this AD, contact Boeing Commercial Airplanes, Attention: Data & Services Management, P.O. Box 3707, MC 2H-65, Seattle, Washington 98124-2207; telephone [phone], extension 1, fax [phone]; e-mail [e-mail]; Internet https://www.myboeingfleet.com. You may review copies of the referenced service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington. For information on the availability of this material at the FAA, call 425-227-1221 or 425-227-1152.

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.gov; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Office (telephone [phone]) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT:

Suk Jang, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to send any written relevant data, views, or arguments about this proposed AD. Send your comments to an address listed under the ADDRESSES section. Include “Docket No. FAA-2008-1364; Directorate Identifier 2008-NM-103-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this proposed AD. We will consider all comments received by the closing date and may amend this proposed AD because of those comments.

We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this proposed AD.

Discussion

We received a report of loss of both the normal electronic flight instrument system (EFIS) cooling supply and the indication of EFIS cooling loss due to a single failure of the battery bus, causing eventual power-down of the EFIS displays; the standby attitude indication is also powered by this battery bus. A single failure of the battery bus can cause loss of attitude indications from both the standby attitude indicator and EFIS displays. An indication of battery bus failure is not displayed on Boeing Model 737-300, -400, and -500 airplanes. The battery bus energizes the standby horizon, the normal supply fan for the equipment cooling system for the EFIS, and the cooling air flow sensor. If the fan does not operate, the EFIS will start to get hot, and when it gets too hot it will automatically stop operation by first going to mono-chromatic, and then, after 60 minutes or more, it will power-down. The supply fan off light will not illuminate to indicate that the fan has failed because it is also powered by the battery bus, which lost power. When this condition occurs, the flightcrew could be left without any attitude indication. Loss of all attitude indications from both the standby indicator and EFIS displays could decrease the ability of the flightcrew to maintain safe flight and landing of the airplane.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-21A1156, Revision 2, dated December 11, 2008. The service bulletin describes procedures for modifying the control power wiring of the normal supply fan and the low flow sensor for the equipment cooling system of the EFIS. The modification includes the following procedures:

• Rerouting the wire for Group 1 airplanes identified in Boeing Alert Service Bulletin 737-21A1156, Revision 1, on which the length of the wire in the W018 wire bundle at the P18 load control center is adequate. If the length of the wire is inadequate, install new wire.
• Rerouting the wire for Group 2 airplanes identified in Boeing Alert Service Bulletin 737-21A1156, Revision 1, on which the length of the wire in the W018 wire bundle at the P18 load control center is adequate. If the length of the wire is inadequate, install new wire.
• Modifying wire bundle W044 between the P6 top disconnect panel and the P6-1 panel for Group 3 airplanes identified in Boeing Alert Service Bulletin 737-21A1156, Revision 1.
• Modifying wire bundle W036 between the P5 forward overhead panel and the mid-center ceiling panel for Group 4 airplanes identified in Boeing Alert Service Bulletin 737-21A1156, Revision 1.

FAA's Determination and Requirements of This Proposed AD

We are proposing this AD because we evaluated all relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of these same type designs. This proposed AD would require accomplishing the actions specified in the service information described previously.

Costs of Compliance

We estimate that this proposed AD would affect 263 airplanes of U.S. registry. The following table provides the estimated costs for U.S. operators to comply with this proposed AD.

Estimated Costs

Action/airplane group	Work hours	Average labor rate per hour	Parts	Cost per product	Number of U.S.-registered airplanes	Fleet cost
Groups 1 & 2 modification	3	$80	0	$240	153	$36,720
Group 4 modification	2	80	0	160	113	18,080

Currently, there are no Group 3 airplanes on the U.S. Register. However, if an affected airplane is imported and placed on the U.S. Register in the future, the required actions would take about 5 work hours, at an average labor rate of $80 per work hour. Based on these figures, we estimate the cost of this AD for Group 3 airplanes to be $400 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 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 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. 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.

You can find our regulatory evaluation and the estimated costs of compliance in the AD Docket.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Incorporation by reference
• 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 FAA amends § 39.13 by adding the following new AD:

Boeing: Docket No. FAA-2008-1364; Directorate Identifier 2008-NM-103-AD.

Comments Due Date

(a) We must receive comments by February 26, 2009.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 737-300, -400, and -500 series airplanes, certificated in any category; as identified in Boeing Alert Service Bulletin 737-21A1156, Revision 2, dated December 11, 2008.

Unsafe Condition

(d) This AD results from a report of loss of both the normal electronic flight instrument system (EFIS) cooling supply and the indication of EFIS cooling loss due to a single failure of the battery bus, causing eventual power-down of the EFIS displays; the standby attitude indication is also powered by this battery bus. We are issuing this AD to prevent loss of all attitude indications from both the standby indicator and EFIS displays, which could decrease the ability of the flightcrew to maintain the safe flight and landing of the airplane.

Compliance

(e) Comply with this AD within the compliance times specified, unless already done.

Modification

(f) Within 24 months after the effective date of this AD: Modify the control power wiring of the normal supply fan and the low flow sensor for the equipment cooling system of the EFIS, by doing all the applicable actions specified in the Accomplishment Instructions of Boeing Alert Service Bulletin 737-21A1156, Revision 2, dated December 11, 2008.

Credit for Actions Done Using Previous Service Information

(g)(1) Actions done before the effective date of this AD in accordance with Boeing Alert Service Bulletin 737-21A1156, Revision 1, dated October 23, 2007, are acceptable for compliance with the corresponding requirements of this AD.

(2) For Groups 1 and 2 airplanes identified in Boeing Alert Service Bulletin 737-21A1156, Revision 1, dated October 23, 2007: Actions done before the effective date of this AD in accordance with Boeing Alert Service Bulletin 737-21A1156, dated June 20, 2006, are acceptable for compliance with the corresponding requirements of this AD.

Alternative Methods of Compliance (AMOCs)

(h)(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, ATTN: Suk Jang, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle ACO, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone]; has the authority to approve AMOCs for this AD, if requested using 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 December 18, 2008.

Stephen P. Boyd,

Assistant Manager, Transport Airplane Directorate, Aircraft Certification Service.