E7-8001. Airworthiness Directives; Learjet Model 31, 31A, 35, 35A (C-21A), 36, 36A, 55, 55B, and 55C Airplanes, and Model 45 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 Learjet Model 31, 31A, 35, 35A (C-21A), 36, 36A, 55, 55B, and 55C airplanes, and Model 45 airplanes. This proposed AD would require inspecting for unsealed gaps on the pylon side of the engine firewall and cleaning/sealing any unsealed gap; and, for certain airplanes, inspecting for unsealed gaps of the pylon trailing edge and cleaning/sealing any gap. This proposed AD results from a report that unsealed gaps (penetration points) of the engine firewall were discovered during production. We are proposing this AD to prevent penetration of flammable liquids or fire through the engine firewall into the engine pylon, which could lead to fire inside the airplane.

DATES:

We must receive comments on this proposed AD by June 11, 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: Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, Washington, DC 20590.
• Fax: [phone].
• Hand Delivery: Room PL-401 on the plaza level of the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Contact Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942, for the service information identified in this proposed AD.

FOR FURTHER INFORMATION CONTACT:

James Galstad, Aerospace Engineer, Systems and Propulsion Branch, ACE-116W, FAA, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas 67209; 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-2007-28016; Directorate Identifier 2006-NM-227-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 Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone [phone]) is located on the plaza level of the Nassif 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

We have received a report indicating that the engine firewall sealing application on certain Learjet Model 45 airplanes does not meet engineering standards, as unsealed gaps (penetration points) of the engine firewall were discovered during production. Further investigation revealed that the same condition could be present on Model 31, 31A, 35, 35A (C-21A), 36, 36A, 55, 55B, and 55C airplanes. Such gaps could include those provided for bleed air, anti-ice, fuel, and fire extinguishing systems, as well as engine mounts, control cables, access panels, and others not described. This condition, if not corrected, could result in penetration of flammable liquids or fire through the engine firewall into the engine pylon, which could lead to fire inside the airplane.

Relevant Service Information

We have reviewed the service bulletins specified in the following table. For all airplanes, the service bulletins describe procedures for inspecting for unsealed gaps on the pylon side of the engine firewall and cleaning/sealing any unsealed gap. For Model 45 airplanes only, Service Bulletin 45-54-3 also describes procedures for inspecting for unsealed gaps on the pylon trailing edge and cleaning/sealing any unsealed gap. Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition.

Applicable Service Information

Learjet airplane model	Service bulletin	Revision level	Date
31/31A	Bombardier Service Bulletin 31-54-2	1	August 21, 2006.
45	Bombardier Service Bulletin 45-54-3	2	August 15, 2003.
35/35A (C-21A) and 36/36A	Learjet Service Bulletin 35/36-54-3	Original	March 16, 2001.
55/55B/55C	Learjet Service Bulletin 55-54-3	Original	March 16, 2001.

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.

Costs of Compliance

There are about 1,243 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 945 airplanes of U.S. registry. The following table provides the estimated costs for U.S. operators to comply with this proposed AD, at an average labor rate of $80 per work hour. Parts and materials may be supplied from operator stores or procured locally.

Estimated Costs to Perform Inspection and Modifications

Learjet airplane model	Work hours	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
31/31A	2	$160	173	$27,680
35/35A (C-21A)	2	160	507	81,120
36/36A	2	160	42	6,720
45	5	400	102	40,800
55/55B/55C	2	160	121	19,360

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):

LEARJET: Docket No. FAA-2007-28016; Directorate Identifier 2006-NM-227-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by June 11, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Learjet Model 31, 31A, 35, 35A (C-21A), 36, 36A, 55, 55B, and 55C airplanes, and Model 45 airplanes; certificated in any category; as identified in the service information specified in Table 1 of this AD.

Table 1.—Applicable Service Information

Learjet airplane model	Service bulletin	Revision level	Date
31/31A	Bombardier Service Bulletin 31-54-2	1	August 21, 2006.
45	Bombardier Service Bulletin 45-54-3	2	August 15, 2003.
35/35A (C-21A) and 36/36A	Learjet Service Bulletin 35/36-54-3	Original	March 16, 2001.
55/55B/55C	Learjet Service Bulletin 55-54-3	Original	March 16, 2001.

Unsafe Condition

(d) This AD results from a report that unsealed gaps (penetration points) of the engine firewall were discovered during production. We are issuing this AD to prevent penetration of flammable liquids or fire through the engine firewall into the engine pylon, which could lead to fire inside 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.

Inspecting, Cleaning, and Sealing of Gaps in Engine Firewall

(f) Within 12 months after the effective date of this AD, do the actions described in paragraphs (f)(1) and (f)(2) of this AD, in accordance with the applicable service information specified in Table 1 of this AD.

(1) For all airplanes: Inspect for unsealed gaps on the pylon side of the engine firewall and clean and seal any unsealed gap.

(2) For Learjet Model 45 airplanes only: Inspect the engine pylon trailing edge for unsealed gaps, and clean and seal any unsealed gap.

Credit for Actions Done Using Previous Service Information

(g) Actions accomplished before the effective date of this AD according to Bombardier Service Bulletin 31-54-2, dated March 16, 2001; or Bombardier Service Bulletin 45-54-3, dated March 16, 2001; or Revision 1, dated December 12, 2001; as applicable; are considered acceptable for compliance with the corresponding action specified in this AD.

Alternative Methods of Compliance (AMOCs)

(h)(1) The Manager, Wichita 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 April 19, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.