2011-26104. Airworthiness Directives; The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.

SUMMARY:

We are revising an earlier proposed airworthiness directive (AD) for the products listed above. That second supplemental NPRM proposed a one-time inspection to determine the part numbers of the aero/fire seals of the blocker doors on the thrust reverser torque boxes on the engines, and replacing affected aero/fire seals with new, improved aero/fire seals. That second supplemental NPRM was prompted by a report that the top 3 inches of the aero/fire seals of the blocker doors on the thrust reverser torque boxes are not fireproof. This action revises the second supplemental NPRM by prohibiting installation of certain non-fireproof thrust reverser seals. We are proposing this third supplemental NPRM to prevent a fire in the fan compartment (a fire zone) from migrating through the seal to a flammable fluid in the thrust reverser actuator compartment (a flammable fluid leakage zone), which could result in an uncontrolled fire. Since these actions impose an additional burden over that proposed in the second supplemental NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.

DATES:

We must receive comments on this supplemental NPRM by November 25, 2011.

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.

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 (phone: [phone]) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT:

Chris Parker, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue SW., Renton, Washington 98057-3356; phone: [phone]; fax: [phone]; e-mail: [e-mail].

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-2006-25001; Directorate Identifier 2006-NM-079-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 issued a second supplemental NPRM to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to all Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. That second supplemental NPRM was published in the Federal Register on July 16, 2009 (74 FR 34518). That second supplemental NPRM proposed to require a one-time inspection to determine the part numbers of the aero/fire seals of the blocker doors on the thrust reverser torque boxes on the engines, and replacing affected aero/fire seals with new, improved aero/fire seals. That second supplemental NPRM also proposed to reduce the compliance time for the replacement of the affected aero/fire seals.

Actions Since Second Supplemental NPRM Was Issued

Since we issued the second supplemental NPRM (74 FR 34518, July 16, 2009), we have determined that it is necessary to propose to prohibit installation of certain non-fireproof thrust reverser seals in this third supplemental NPRM, because we have received information indicating that some thrust reversers with non-fireproof seals could be installed on certain airplanes.

Comments

We gave the public the opportunity to comment on the second supplemental NPRM (74 FR 34518, July 16, 2009). The following presents the comments received on the second supplemental NPRM and the FAA's response to each comment.

Request To Include Parts Installation Paragraph

Boeing requested that the second supplemental NPRM (74 FR 34518, July 16, 2009) be revised to address spare thrust reverser halves being installed on any Model 737 Next Generation airplane. Boeing explained that some spare thrust reverser halves could be equipped with non-fireproof seals and that if these spare units are installed after the inspection, some airplanes will have non-fireproof seals.

We partially agree. While we explained in the first supplemental NPRM (73 FR 51382, September 3, 2008) that we understood affected spare assemblies had been purged from the parts supply system, we have now received information that thrust reverser interchangeability instructions might allow older thrust reverser seals having part number (P/N) 315A2245-1 or 315A2245-2 to be installed on newly delivered airplanes. While we cannot apply the inspections proposed by this third supplemental NPRM to spare parts, we can require that parts being installed on the airplane be compliant with this third supplemental NPRM. We have added paragraph (i) to this third supplemental NPRM to prohibit installation of non-fireproof thrust reverser seals.

Requests To Extend Compliance Time for Replacement

The Air Transport Association (ATA), on behalf of two member airlines (Air Tran Airways and American Airlines), and Boeing requested that we change the proposed compliance time for the replacement of the aero/fire seals specified in paragraph (h) of the second supplemental NPRM (74 FR 34518, July 16, 2009).

Air Tran Airways (Air Tran) explained that the second supplemental NPRM (74 FR 34518, July 16, 2009) proposed to allow up to 60 months or 8,200 flight cycles after the effective date of the AD to comply with the proposed inspection specified in paragraph (g) of the second supplemental NPRM. However, Air Tran pointed out that if a non-fireproof aero/fire seal is found on a thrust reverser, the seal must be changed prior to further flight. Air Tran reasoned that the second supplemental NPRM should allow a more realistic time frame to have the seal replaced. Air Tran provided no technical justification for this request.

Boeing explained that the compliance time from the original NPRM (71 FR 34025, June 13, 2006) should be used, regardless of when the inspection for aero/fire seals of the thrust reverser torque boxes on the engines was done. Boeing stated that the second supplemental NPRM (74 FR 34518, July 16, 2009) would likely ground airplanes because operators would only accomplish the inspections if they have replacement seals on hand; Boeing only carries limited quantities of the seals and the re-order lead time for these seals is approximately 20 weeks.

We agree to revise this third supplemental NPRM to change the proposed compliance time specified in paragraph (h) of this third supplemental NPRM. However, we are revising the compliance time in paragraph (h) of this third supplemental NPRM to specify that operators have within 6 months after doing the inspection in paragraph (g) of this third supplemental NPRM to replace a non-fireproof seal. Under the provisions of paragraph (k) of this third supplemental NPRM, we will consider requests for approval of an alternative method of compliance (AMOC) that provides an acceptable level of safety, if parts availability becomes a problem. We have determined that replacement of the non-fireproof seal within 6 months after doing the inspection in paragraph (g) of this third supplemental NPRM will not adversely affect safety. We have revised this third supplemental NPRM accordingly.

Request To Specify Terminating Action

The ATA, on behalf of its member American Airlines, requested that the replacement of the non-fireproof seal be done in accordance with Boeing Special Attention Service Bulletin 737-78-1074, Revision 1, dated September 15, 2005, and that the proposed AD state that this replacement is terminating action.

We agree that the replacement of the non-fireproof seals can be done in accordance with Boeing Special Attention Service Bulletin 737-78-1074, Revision 1, dated September 15, 2005, and that the replacement of the non-fireproof seals is terminating action for the inspection required by paragraph (g) of this third supplemental NPRM. We have added this information to paragraph (h) of this AD.

Requests To Apply AD to Part Rather Than Airplane

The ATA, on behalf of its member Air Tran, and Boeing requested that the second supplemental NPRM (74 FR 34518, July 16, 2009) apply only to thrust reverser assemblies having certain part numbers as opposed to applying to the airplane.

Air Tran explained that thrust reversers are rotable, line replaceable unit assemblies, which may be uninstalled, stand-alone spares, and can be rotated among other airplanes. For this reason, Air Tran suggested that the applicability of the second supplemental NPRM (74 FR 34518, July 16, 2009) should be against thrust reverser assembly part numbers rather than the airplane.

Boeing explained that the proposed applicability in the second supplemental NPRM (74 FR 34518, July 16, 2009) is open-ended and would apply to new Model 737 airplanes that are already compliant. Boeing explained further that thrust reversers having part number (P/Ns) 315A2295-195 through 315A2295-500 were delivered with seals with a fireproof section, and that interchangeability definitions for thrust reversers having P/Ns 315A2245-7 and 315A2245-8 (fireproof section) do not allow these seals to be replaced with seals having P/Ns 315A2245-1 and 315A2245-2 (non-fireproof). Boeing recommended limiting the proposed applicability to thrust reversers having P/Ns 315A2295-3 through 315A2295-194, and P/Ns 315A2295-503 through 315A2295-694.

We disagree to change the applicability of this third supplemental NPRM to apply to thrust reversers having certain part numbers. The seal is not integral to the thrust reverser and is replaceable. Therefore, a non-fireproof seal could be used on any thrust reverser—even a thrust reverser originally built with a compliant fireproof seal. It is the operator's responsibility to maintain compliance once an AD has been accomplished. The operator must ensure that the thrust reversers on its airplanes have been inspected and are using a fireproof seal. If an operator replaces a thrust reverser, the thrust reverser must be inspected to ensure compliance with this third supplemental NPRM. We have not changed the applicability of this third supplemental NPRM in this regard.

However, we have determined that the inspection required by paragraph (g) of this third supplemental NPRM is only necessary for certain airplanes. Therefore, we have revised paragraph (g) of this third supplemental NPRM to specify that only the following airplanes are subject to the requirements of that paragraph: “For airplanes having an original airworthiness certificate issued before the effective date of this AD, and for airplanes on which the date of issuance of the original export certificate of airworthiness is before the effective date of this AD * * * .”

Request for Clarification of Use of Illustrated Parts Catalog (IPC) as Maintenance Record

All Nippon Airways (ANA) requested that we clarify if their IPC can be used as a form of maintenance record to identify if the airplane has the fireproof seal installed. ANA explained that the seals are not controlled by any type of part-control system, and that operators visually verify the stamped part number instead. ANA stated that since the stamped part number is often unreadable, the operator would be forced to replace the seal in order to remain in compliance with the AD, regardless if the seal was already a fireproof seal. ANA asserted that replacing a possible fireproof seal (to remain in compliance with the proposed AD) simply because the part number is unreadable, is an unreasonable action.

We disagree to allow use of the IPC as a maintenance record. If the required maintenance records, which do not include the IPC, are not available to show that the correct fireproof seal has been installed, and the part number is worn off the aero/fire seals, it is still possible to verify that the correct part is installed by visually inspecting the seal for color content, as specified in paragraph (g) of the second supplemental NPRM. We have not changed this third supplemental NPRM in this regard.

Request for Clarification of the Difference in the Applicability Between the Original NPRM and the Second Supplemental NPRM

ANA also requested that we clarify the difference in the applicability between the original NPRM (71 FR 34025, June 13, 2006) and the second supplemental NPRM (74 FR 34518, July 16, 2009). ANA explained that the applicability in the original NPRM was for all Model 737-600, -700,-700C, -800, and -900 series airplanes, which is what is listed in Boeing Special Attention Service Bulletin 737-78-1074, Revision 1, dated September 15, 2005 (referenced in the original NPRM as the source of service information for replacing aero/fire seals).

We agree to clarify differences in the applicability of the various NPRMs. The applicability of the original NPRM (71 FR 34025, June 13, 2006) referenced that service bulletin for affected airplanes. After we issued the original NPRM, we received information on the interchangeability of the affected aero/fire seals. The applicability of the first supplemental NPRM (73 FR 51382, September 3, 2008) was revised to specify “all” Model 737 airplanes (including Model 737-900ER series airplanes, which had been added to the U.S. type certificate data sheet), since all of these airplanes could be affected by the interchangeability of the seals. No change to this third supplemental NPRM is necessary in this regard.

Explanation of Change Made to This Proposed AD

We have revised this proposed AD to identify the legal name of the manufacturer as published in the most recent type certificate data sheet for the affected airplane models.

FAA's Determination

We are proposing this third supplemental NPRM because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of these same type designs. Certain changes described above expand the scope of the second supplemental NPRM (74 FR 34518, July 16, 2009). As a result, we have determined that it is necessary to reopen the comment period to provide additional opportunity for the public to comment on this third supplemental NPRM.

Explanation of Change to Costs of Compliance

Since issuance of the original NPRM (71 FR 34025, June 13, 2006), we have increased the labor rate used in the Costs of Compliance from $80 per work-hour to $85 per work-hour. The Costs of Compliance information, below, reflects this increase in the specified labor rate.

Costs of Compliance

We estimate that this proposed AD affects 803 airplanes of U.S. registry.

We estimate the following costs to comply with this proposed AD:

Estimated Costs

Action	Labor cost	Parts cost	Cost per product	Cost on U.S. operators
Inspection for part number	1 work-hour × $85 per hour = $85 per inspection cycle	None	$85 per inspection cycle	$68,255 per inspection cycle.

We estimate the following costs to do any necessary replacements that would be required based on the results of the proposed inspection. We have no way of determining the number of aircraft that might need this replacement:

On-condition Costs

Action	Labor cost	Parts cost	Cost per product
Replacement	5 work-hours × $85 per hour = $425	$4,770	$5,195

According to the manufacturer, some of the costs of this proposed AD may be covered under warranty, thereby reducing the cost impact on affected individuals. We do not control warranty coverage for affected individuals. As a result, we have included all costs in our cost estimate.

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),

(3) Will not affect intrastate aviation in Alaska, and

(4) 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.

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 airworthiness directive (AD):

The Boeing Company: Docket No. FAA-2006-25001; Directorate Identifier 2006-NM-079-AD.

Comments Due Date

(a) We must receive comments by November 25, 2011.

Affected ADs

(b) None.

Applicability

(c) This AD applies to all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes, certificated in any category.

Subject

(d) Joint Aircraft System Component (JASC)/Air Transport Association (ATA) of America Code 78: Engine exhaust.

Unsafe Condition

(e) This AD was prompted by a report that the top 3 inches of the aero/fire seals of the blocker doors on the thrust reverser torque boxes are not fireproof. We are issuing this AD to prevent a fire in the fan compartment (a fire zone) from migrating through the seal to a flammable fluid in the thrust reverser actuator compartment (a flammable fluid leakage zone), which could result in an uncontrolled fire.

Compliance

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

Inspection to Determine Type of Aero/Fire Seals

(g) For airplanes having an original airworthiness certificate issued before the effective date of this AD, and for airplanes on which the date of issuance of the original export certificate of airworthiness is before the effective date of this AD: Within 60 months or 8,200 flight cycles, whichever occurs first, after the effective date of this AD, perform a one-time detailed inspection to determine the color of the aero/fire seals of the blocker doors on the thrust reverser torque boxes on the engines. For any aero/fire seal having a completely grey color (which is the color of seals with part number (P/N) 315A2245-1 or 315A2245-2), with no red at the upper end of the seal, do the actions specified in paragraph (h) of this AD. For any aero/fire seal having a red color at the upper end of the seal (which indicates installation of seals with P/N 315A2245-7 or 315A2245-8), no further action is required by this AD. A review of airplane maintenance records is acceptable in lieu of this inspection if from that review the part number of the correct aero/fire seals (P/N 315A2245-7 or -8) can be conclusively determined to be installed.

Note 1:

For the purposes of this AD, a detailed inspection is: “An intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at an intensity deemed appropriate. Inspection aids such as mirrors, magnifying lenses, etc., may be necessary. Surface cleaning and elaborate procedures may be required.”

Replacement of the Aero/Fire Seals

(h) For any aero/fire seal identified during the inspection/records check required by paragraph (g) of this AD to have a non-fireproof seal: Within six months after doing the actions required by paragraph (g) of this AD, replace the aero/fire seals of the blocker doors on the thrust reverser torque boxes on the engines with new, improved aero/fire seals, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-78-1074, Revision 1, dated September 15, 2005. Replacing the aero/fire seals of the blocker doors on the thrust reverser torque boxes on the engines with new, improved aero/fire seals, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-78-1074, Revision 1, dated September 15, 2005, is terminating action for the inspection required by paragraph (g) of this AD.

Parts Installation

(i) As of the effective date of this AD, no person may install a non-fireproof thrust reverser seal having P/N 315A2245-1 or P/N 315A2245-2 on any airplane.

Credit for Actions Accomplished in Accordance with Previous Service Information

(j) Replacements done before the effective date of this AD in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-78-1074, dated April 7, 2005, are acceptable for compliance with the requirements of paragraph (h) of this AD.

Alternative Methods of Compliance (AMOCs)

(k)(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request to your principal inspector or local Flight Standards District Office, as appropriate. If sending information directly to the manager of the ACO, send it to the attention of the person identified in the Related Information section of this AD. Information may be e-mailed to: [e-mail].

(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the local flight standards district office/certificate holding district office.

Related Information

(l) For more information about this AD, contact Chris Parker, Aerospace Engineer, Propulsion Branch, ANM-140S, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; phone: [phone]; fax: [phone]; e-mail: [e-mail].

(m) 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.

Issued in Renton, Washington, on September 30, 2011.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.