E8-1135. Airworthiness Directives; Airbus Model A318, A319, A320, and A321 Series Airplanes Equipped With Certain Northrop Grumman (Formerly Litton) Air Data Inertial Reference Units

AGENCY:

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

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Airbus Model A319, A320, and A321 series airplanes equipped with certain Litton air data inertial reference units (ADIRUs). The existing AD currently requires modifying the shelf (floor panel) above ADIRU 3, modifying the polycarbonate guard that covers the ADIRUs for certain airplanes, and modifying the ladder located in the avionics compartment for certain airplanes. This proposed AD would require those modifications on additional airplanes. This proposed AD would also require replacing all three ADIRUs with improved ADIRUs. This proposed AD also adds Model A318 series airplanes to the applicability. This proposed AD results from reports that “NAV IR FAULT” messages have occurred during takeoff due to failure of an ADIRU and subsequent analysis showing that the shelf modification has not sufficiently addressed failure of an ADIRU. We are proposing this AD to prevent failure of an ADIRU during flight, which could result in loss of one source of critical attitude and airspeed data and reduce the ability of the flightcrew to control the airplane.

DATES:

We must receive comments on this proposed AD by February 25, 2008.

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 Airbus, 1 Rond Point Maurice Bellonte, 31707 Blagnac Cedex, France.

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:

Tim Dulin, Aerospace Engineer, International Branch, ANM-116, Transport Airplane Directorate, FAA, 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-2008-0046; Directorate Identifier 2007-NM-270-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

On December 12, 2003, we issued AD 2003-26-03, amendment 39-13399 (68 FR 74172, December 23, 2003), for certain Airbus Model A319, A320, and A321 series airplanes equipped with certain Litton air data inertial reference units (ADIRUs). That AD requires modifying the shelf (floor panel) above ADIRU 3, and, for certain airplanes, modifying the polycarbonate guard that covers the ADIRUs, and the ladder located in the avionics compartment, as applicable. That AD resulted from reports that “NAV IR FAULT” messages have occurred during takeoff due to failure of ADIRU 3 on several Model A319, A320, and A321 series airplanes. We issued that AD to prevent failure of ADIRU 3 during flight, which could result in loss of one source of critical attitude and airspeed data and reduce the ability of the flightcrew to control the airplane.

Actions Since Existing AD Was Issued

Since we issued AD 2003-26-03, the European Aviation Safety Agency (EASA), which is the Technical Agent for the Member States of the European Union, notified us that further analysis has shown that modifying the ADIRU shelf has not sufficiently addressed the unsafe condition. The clearance between the shelf and ADIRUs is still too small. Consequently, vibration during takeoff could cause the shelf to hit the top of an ADIRU, leading to loss of parameters (attitude, vertical speed, ground speed, etc.). The EASA has determined that, in addition to modifying the ADIRU shelf, all three ADIRUs must be replaced with improved ADIRUs that introduce a more robust shock resistance to adequately address the unsafe condition. The EASA has also determined that the unsafe condition exists on certain Model A318 series airplanes.

Relevant Service Information

Airbus has issued Service Bulletin A320-34-1350, dated March 20, 2006. The service bulletin describes procedures for replacing all three ADIRUs with improved ADIRUs having part number 465020-0303-0316, which introduce a more robust shock resistance and new magnetic variation tables.

Airbus has also issued Service Bulletin A320-25-1248, Revision 01, dated April 16, 2003. The procedures in Revision 01 of the service bulletin are essentially the same as those in the original issue of the service bulletin, dated February 16, 2001. Revision 1 of the service bulletin adds airplanes to the effectivity of the service bulletin.

Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition. The EASA mandated the service information and issued airworthiness directive 2007-0217, dated August 9, 2007, to ensure the continued airworthiness of these airplanes in the European Union.

FAA's Determination and Requirements of the Proposed AD

These airplanes are manufactured in France and are type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. As described in FAA Order 8100.14A, “Interim Procedures for Working with the European Community on Airworthiness Certification and Continued Airworthiness,” dated August 12, 2005, the EASA has kept the FAA informed of the situation described above. We have examined the EASA's findings, evaluated all pertinent information, and determined that AD action is necessary for airplanes of this type design that are certificated for operation in the United States.

This proposed AD would supersede AD 2003-26-03 and retain the requirements of the existing AD. This proposed AD would also require accomplishing the actions specified in the service information described previously.

Change to Existing AD

This proposed AD would retain all requirements of AD 2003-26-03. Since AD 2003-26-03 was issued, the AD format has been revised, and certain paragraphs have been rearranged. As a result, the requirement in paragraph (a) of AD 2003-26-03 corresponds to paragraph (f) of this proposed AD.

Costs of Compliance

This proposed AD would affect about 658 airplanes of U.S. registry.

The actions that are required by AD 2003-26-03 and retained in this proposed AD take about 4 work hours per airplane, at an average labor rate of $80 per work hour. Required parts cost about $300 per airplane. Based on these figures, the estimated cost of the currently required actions for U.S. operators is $407,960, or $620 per airplane.

The new proposed actions would take about 3 work hours per airplane, at an average labor rate of $80 per work hour. The manufacturer states that it will supply the required parts to operators at no cost. Based on these figures, the estimated cost of the new actions specified in this proposed AD for U.S. operators is $157,920, or $240 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 removing amendment 39-13399 (68 FR 74172, December 23, 2003) and adding the following new airworthiness directive (AD):

Airbus: Docket No. FAA-2008-0046; Directorate Identifier 2007-NM-270-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by February 25, 2008.

Affected ADs

(b) This AD supersedes AD 2003-26-03.

Applicability

(c) This AD applies to Airbus Model A318, A319, A320, and A321 series airplanes, certificated in any category; equipped with at least one Northrop Grumman (formerly Litton) air data inertial reference unit (ADIRU), part number (P/N) 465020-0303-0307, -0308, -0309, -0312, -0314, -0315, or -0316; except airplanes equipped with three ADIRUs having P/N 465020-0303-0316 and on which Airbus Modification 30650 or 30872 has been incorporated in production.

Unsafe Condition

(d) This AD results from reports that “NAV IR FAULT” messages have occurred during takeoff due to failure of an ADIRU and subsequent analysis showing that the shelf modification has not sufficiently addressed failure of an ADIRU. We are issuing this AD to prevent failure of an ADIRU during flight, which could result in loss of one source of critical attitude and airspeed data and reduce the ability of the flightcrew to control 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.

Restatement of Requirements of AD 2003-26-03

Modification

(f) For Model A319, A320, and A321 series airplanes, equipped with any Litton ADIRU installed in accordance with Airbus Modification 24852, 25108, 25336, 26002, or 28218: Within 2 years after January 27, 2004 (the effective date of AD 2003-26-03), do the modifications specified in paragraphs (f)(1), (f)(2), and (f)(3) of this AD, as applicable, in accordance with paragraphs A. through D. of the Accomplishment Instructions of Airbus Service Bulletin A320-25-1248, dated February 16, 2001; or Airbus Service Bulletin A320-25-1248, Revision 01, dated April 16, 2003; as applicable.

(1) For all airplanes: Modify the shelf (floor panel) above ADIRU 3 by installing shims between the shelf and the webs of the shelf support structure.

(2) For airplanes with Airbus Modification 25900P3941 or Airbus Service Bulletin A320-25-1200 accomplished as of January 27, 2004: Modify the polycarbonate guard (umbrella) protecting the ADIRUs by installing shims between the guard and the shelf support structure.

(3) For airplanes with Airbus Modification 23027P2852 or Airbus Service Bulletin A320-52-1038 accomplished as of January 27, 2004: Modify the ladder located in the avionics compartment by machining the slot at the foot of the ladder to increase the depth by 0.236 inch.

New Requirements of This AD

Modification for Certain Airplanes

(g) For all airplanes equipped with any ADIRU installed in accordance with Airbus Modification 31070, 31742, or 35517, except airplanes on which Airbus Modification 30650 or 30872 has been accomplished in production: Within 46 months after the effective date of this AD, modify the ADIRU shelf supports by accomplishing all of the applicable actions specified in the Accomplishment Instructions of Airbus Service Bulletin A320-25-1248, Revision 01, dated April 16, 2003.

Replacement of ADIRUs

(h) For all airplanes except those on which Airbus Modification 35517 has been incorporated in production: Within 46 months after the effective date of this AD, replace all three ADIRUs with improved ADIRUs having P/N 465020-0303-0316 in accordance with the Accomplishment Instructions of Airbus Service Bulletin A320-34-1350, dated March 20, 2006.

Alternative Methods of Compliance (AMOCs)

(i)(1) The Manager, International Branch, ANM-116, Transport Airplane Directorate, 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.

Related Information

(j) European Aviation Safety Agency airworthiness directive 2007-0217, dated August 9, 2007, also addresses the subject of this AD.

Issued in Renton, Washington, on January 14, 2008.

Stephen P. Boyd,

Assistant Manager, Transport Airplane Directorate, Aircraft Certification Service.