Airworthiness Directives; Cessna Aircraft Company 300 and 400 Series Airplanes

[Federal Register Volume 64, Number 128 (Tuesday, July 6, 1999)] [Proposed Rules] [Pages 36307-36318] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 99-16752]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-CE-67-AD] RIN 2120-AA64

Airworthiness Directives; Cessna Aircraft Company 300 and 400 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes to supersede Airworthiness Directive (AD) 75-23-08 R5, which currently requires repetitively inspecting and replacing or repairing the exhaust system on certain Cessna Aircraft Company (Cessna) 300 and 400 series airplanes. The proposed AD would replace the inspections and replacements that are required by AD 75-23- 08 R5 with inspections and replacements containing new simplified procedures for all 300 and 400 series airplanes (models affected by the current AD plus additional models). The proposed AD would also revise the inspection intervals and would require replacing certain unserviceable parts and removing the exhaust system for detailed inspections at regular intervals. The proposed AD is the result of numerous incidents and accidents relating to the exhaust systems on Cessna 300 and 400 series airplanes dating from the middle 1970's to the present, including six incidents since issuance of AD 75-23-08 R5 where exhaust problems were cited. The actions specified by the proposed AD are intended to detect and correct cracks and corrosion in the exhaust system, which could result in exhaust system failure and a possible uncontrollable in-flight fire with pilot and/or passenger injury.

DATES: Comments must be received on or before August 9, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation Administration (FAA), Central Region, Office of the Regional Counsel, Attention: Rules Docket No. 97-CE-67-AD, Room 1558, 601 E. 12th Street, Kansas City, Missouri 64106. Comments may be inspected at this location between 8 a.m. and 4 p.m., Monday through Friday, holidays excepted.

FOR FURTHER INFORMATION CONTACT: Paul O. Pendleton, Aerospace Engineer, FAA, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Wichita, Kansas 67209; telephone: (316) 946-4143; facsimile: (316) 946-4407.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Communications should identify the Rules Docket number and be submitted in triplicate to the address specified above. The FAA believes that the proposed regulation may have a significant economic impact on a substantial number of small businesses. Due to the urgent nature of the safety issues addressed, the FAA has been unable to complete a preliminary regulatory flexibility analysis prior to issuance of the NPRM. A final regulatory flexibility analysis will be completed before, or within 180 days of issuance of, the final rule. To assist in this analysis, the FAA is particularly interested in receiving information on the impact of the proposed rule on small businesses and suggested alternative methods of compliance that reduce or eliminate such impacts. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this notice may be changed in light of the comments received. Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket.

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Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket No. 97-CE-67-AD.'' The postcard will be date stamped and returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Central Region, Office of the Regional Counsel, Attention: Rules Docket No. 97-CE-67-AD, Room 1558, 601 E. 12th Street, Kansas City, Missouri 64106.

Discussion

AD 75-23-08 R5, Amendment 39-5451, currently requires repetitively inspecting, using visual methods, the exhaust system on certain Cessna 300 and 400 series airplanes; and repairing or replacing any unserviceable parts. Cessna and the FAA performed extensive investigation and found the following possible causes and effects of these exhaust problems:

--Significant vibration between the beam-mounted engine and the firewall-mounted turbocharger; --Leaking exhaust gases, which can cause fuel line failure because the fuel lines behind the firewall overheat and rupture. (Most of these fuel lines cannot be isolated or shut-off); --Reduced structural strength of the engine mount beams and canted bulkheads as a result of exposure to high heat, which could compromise the engine installation; and --Structural failure of the wing or loss of flight control that results from an in-flight fire.

The FAA issued AD 75-23-08 and five subsequent revisions to this AD, including the current one referenced above, as an attempt to manage these problems through repetitive visual inspections.

Actions Since Issuance of Previous Rule

In the 20 plus years since the issuance of AD 75-23-08, failures of exhaust systems on Cessna 300 and 400 series airplanes have continued to occur and have contributed to fatalities. The FAA, the National Transportation Safety Board (NTSB), and Cessna have conducted numerous tests and analysis on the exhaust system configurations in an attempt to resolve the repeated problems and to alleviate these failures. The FAA and the NTSB have issued several safety recommendations to provide guidance on how to alleviate problems with the exhaust systems on Cessna 300 and 400 series airplanes. From these recommendations, the FAA has developed new service information (included as an Appendix to this AD) and Cessna has revised the maintenance and service manuals. The FAA believes that this new information should help to reduce the confusion of the requirements in the current action and simplify the procedures. A recent fatal accident has occurred involving a Cessna Model 421B airplane. While not implicated in the cause of the accident, the FAA and the NTSB have determined that the exhaust system on the accident airplane was in a condition of imminent catastrophic failure. The airplane records indicate that the exhaust system inspection and replacement requirements of AD 75-23-08 R5 had been accomplished.

The FAA's Determination

After examining the circumstances and reviewing all available information related to the incidents described above, including the referenced service information, the FAA has determined that AD action should be taken to detect and correct cracks and corrosion in the exhaust system, which could result in exhaust system failure and a possible uncontrollable in-flight fire. Exposure to these conditions could cause injury to the pilot and passengers during flight.

Explanation of the Provisions of the Proposed AD

Since an unsafe condition has been identified that is likely to exist or develop in other Cessna 300 and 400 series airplanes of the same type design, the FAA is proposing an AD to supersede AD 75-23-08 R5. The proposed AD would replace the inspections and replacements that are required by AD 75-23-08 R5 with inspections and replacements containing new simplified procedures for all 300 and 400 series airplanes (models affected by the current AD plus additional models). The proposed AD would also revise the inspection intervals and would require replacing certain unserviceable parts and removing the exhaust system for detailed inspections at regular intervals. Provisions of the proposed AD include:

--Prohibiting patch-type repairs; and --Removing the exhaust system and sending it to a designated facility for metallic identification, airworthiness determinations, and repair or replacement of any unserviceable parts.

Service Information

In the future, Cessna may develop service information or additional maintenance and/or service manual revisions to address this issue. The FAA will issue alternative methods of compliance to this AD if the procedures are deemed acceptable to address the unsafe condition specified in the proposed AD.

Cost Impact

The FAA estimates that 6,500 airplanes in the U.S. registry would be affected by the proposed AD. The cost of the proposed inspections would be as follows at an average labor rate of approximately $60 per hour. The cost of any necessary repair depends on the extent of the rework and replacement needed based on the results of the proposed inspections.

--The proposed repetitive 50-hour time-in-service (TIS) visual inspections of the exhaust system would take approximately 3 workhours to accomplish, with a labor cost of $180 per airplane for each inspection; --The proposed repetitive 100-hour TIS visual inspections of the removed tailpipes would take approximately 1 workhour per tailpipe to accomplish, with a labor cost of $120 per airplane for each proposed inspection; --The proposed inspection of the engine beams and canted bulkheads, as a result of damage to the tailpipes, would take approximately 3 workhours to accomplish, with a labor cost of $180 per airplane; --The proposed inspection of the fuel tubing behind the firewall, as a result of damage to the tailpipes, engine beams, and canted bulkheads, would take approximately 16 workhours to accomplish, with a labor cost of $960 per airplane; --The proposed replacement of the fuel tubing, if necessary, would take approximately 30 workhours to accomplish, with a labor cost of $1,800 per airplane; --The proposed 500-hour TIS proposed requirement of removing and shipping the exhaust system to an approved facility would take approximately 8 workhours, with a labor cost of $480. The cost of shipping the exhaust system to the facility and the inspections by the facility is estimated at $500; --The proposed repetitive pressure test is estimated to take 1 workhour, with a labor cost of $60 per airplane; and --The proposed V-band clamp replacement is estimated to take 1 workhour, with a labor cost of $60 per airplane.

The total cost impact on the U.S. operators for the proposed initial inspections is estimated to be

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$28,210,000, or $4,340 per airplane. The maximum expense for full exhaust parts replacement is estimated to be approximately $60,000 per airplane. These figures do not take into the account the costs of any repetitive inspections or repairs or replacements that would be necessary if the FAA adopted the proposed rule. The FAA has no way of determining the number of repetitive inspections an owner/operator will incur over the life of the airplane, or the extent of the repairs and replacements that may be necessary for any affected airplane.

Compliance Time of This AD

Certain repetitive inspections of the proposed AD are presented in both calendar time and hours time-in-service (TIS). The unsafe condition specified in the proposed AD is a result of the stress cracking and/or corrosion that results over time. Stress corrosion starts as a result of high local stress incurred through operation of the affected part (the exhaust systems). Corrosion can then develop regardless of whether the airplane is in operation. The cracks may not be noticed initially as a result of the stress loads, but could then progress as a result of corrosion. The stress incurred during flight operations (while in-flight) or temperature changes (either while in- flight or on the ground) could then cause rapid crack growth. In order to assure that these stress corrosion cracks do not go undetected, a compliance time of specific hours TIS and calendar time (whichever occurs first) is proposed.

Regulatory Impact

The regulations proposed herein would not have substantial direct effects 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. Therefore, in accordance with Executive Order 12612, it is determined that this proposal would not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. For the reasons discussed above, I certify that this action (1) Is not a ``significant regulatory action'' under Executive Order 12866; (2) is not a ``significant rule'' under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated, may have a significant economic impact on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. The FAA is currently conducting a Regulatory Flexibility Determination and Analysis and has considered alternatives to the proposed AD that could minimize the impact on small entities. After careful consideration, the FAA determined that AD action is the best course of action to address the unsafe condition specified in this document; and (2) the situation does not warrant waiting for the completion of the Regulatory Flexibility Determination and Analysis before issuing the NPRM. When completed, a copy of the Regulatory Flexibility Determination and Analysis will be placed in the Docket file and can be obtained at the address specified in the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend 14 CFR part 39 of the Federal Aviation Regulations 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.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by removing Airworthiness Directive (AD) 75-23-08 R5, Amendment 39-5451, and by adding a new AD to read as follows:

Cessna Aircraft Company: Docket No. 97-CE-67-AD; Supersedes AD 75- 23-08 R5, Amendment 39-5451.

Applicability: Models T310P, T310Q, T310R, 320, 320A, 320B, 320C, 320D, 320E, 320F, 320-1, 335, 340, 340A, 321 (Navy OE-2), 401, 401A, 401B, 402, 402A, 402B, 402C, 404, 411, 411A, 414, 414A, 421, 421A, 421B, and 421C airplanes, all serial numbers, certificated in any category.

Note 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (k) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated in the compliance table in Figure 1 of this AD, unless already accomplished. To detect and correct cracks and corrosion in the exhaust system, which could result in exhaust system failure and a possible uncontrollable in-flight fire with pilot and/or passenger injury, accomplish the following: (a) The following paragraphs present the type of individuals who have the authority to accomplish the actions of this AD: (1) Repairs: Required to be accomplished at an FAA-approved repair facility. (2) Replacements: Required to be accomplished in accordance with the appropriate Cessna Service Manual and must be accomplished by a person holding a currently effective mechanic certificate with both an airframe and powerplant (A&P) rating or by an individual authorized to represent an FAA-approved repair station. (3) Visual inspections except for paragraphs (f) and (i) of this AD: Required to be accomplished by a person holding a currently effective mechanic certificate with both an airframe and powerplant (A&P) rating.

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(b) At the compliance time specified in Figure 1 of this AD, visually inspect the exhaust system for burned areas, cracks, or looseness. If any area of the exhaust system shows damage as defined in the Appendix of this AD, prior to further flight, repair or replace the damaged part. (c) At the compliance time specified in Figure 1 of this AD, remove the tailpipes and visually inspect for cracks, corrosion, holes, or distortion. (1) If no crack, corrosion, hole, or distortion is found, continue to visually inspect at intervals indicated in Figure 1 of this AD. (2) If a crack, corrosion, hole, or distortion is found during any inspection, prior to further flight, repair or replace the tailpipe. (3) When a new tailpipe is installed after the effective date of this AD, terminate the 100-hour time-in-service (TIS) repetitive inspections required as specified in Figure 1 of this AD until the accumulation of 500 hours TIS or 5 years from the installation date, whichever occurs first, at which time continue the 100-hour TIS inspection intervals. (d) At the compliance time specified in Figure 1 of this AD, visually inspect the outboard engine beam (adjacent to the tailpipe) and the canted bulkheads for signs of distress, chafing, corrosion, or cracking. Even though some airplanes may have stainless steel engine beams, carefully inspect the areas of contact between the engine beam and canted bulkhead for corrosion. (1) If damage to the engine beams is found or there is evidence of overheating on the firewall, prior to further flight, replace the firewall and the aluminum fuel lines behind the firewall. Stainless steel fuel lines are available from the Cessna Aircraft Company. Replacement of the fuel lines behind the firewall may require removing and replacing the firewall or accomplishing major repair of the firewall. (2) Prior to further flight, repair any distress, chafing, corrosion, or cracking on the engine beams or canted bulkheads in accordance with data provided by any individual or facility that is authorized by the FAA to perform the necessary repairs or provide the FAA-approved data to authorized personnel for repair of these items. (e) At the compliance time specified in Figure 1 of this AD, inspect the exhaust system and perform a pressure test in accordance with the Appendix of this AD. If any condition as specified in the Appendix of this AD is found, prior to further flight, repair or replace the affected parts. (f) At the compliance time specified in Figure 1 of this AD, remove the exhaust system from the slip joints and aft to all turbocharger-attached components and send to an FAA-approved manufacturing and repair facility that is authorized by the FAA to perform material and condition determinations, and prior to further flight, accomplish any necessary repairs on these items.

Note 2: The following repair facilities have been approved as of the effective date of this AD. A current list of FAA-approved facilities can be obtained from the FAA, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Wichita, Kansas 67209; Attention: Paul O. Pendleton, Aerospace Engineer; telephone: (316) 946-4143; facsimile: (316) 946-4407:

Wall Colmony Corp., 4700 S.E. 59th St., Oklahoma City, OK 73135, (405) 672-1361 Knisley Welding Inc., 3450 Swetzer Road, Loomis, CA 95650, (916) 652-5891 Heliarc Welding Service, 3965 Newport St., 73135 Denver, CO 80207- 73135, (303) 672-1361

Note 3: The FAA-approved manufacturing and repair facilities will perform the following and provide information to be utilized for future actions required by this AD: Determine the airworthiness of the exhaust system parts; Measure for the minimum acceptable material thickness of .025 inch; Determine the airworthiness of previous repairs (multi- seam welds and patch-type welds are not considered airworthy); Repair or replace all unserviceable parts (no multi- seam or patch-type weld repairs are permitted); Determine the material type of the exhaust system (i.e., Inconel or stainless steel); and Stamp the material type with an ``I'' for Inconel or ``SS'' for stainless steel, the name of the facility making the determination, and the date on the exhaust system.

(g) At the compliance time specified in Figure 1 of this AD, replace all V-band clamps per the appropriate Cessna Service Manual. (h) At the compliance time specified in Figure 1 of this AD, disassemble and visually inspect the slip joint for freedom of motion. If the slip joint is seized or frozen, prior to further flight, replace the slip joint. (i) At the compliance time specified in Figure 1 of this AD, remove the exhaust system from the slip joints and aft to all turbo- charger attached components, and send to any FAA-approved exhaust repair facility. The FAA-approved exhaust repair facility will inspect this portion of the exhaust system for serviceable condition and make any necessary repairs to these items. No patch-type or multi-seam weld repairs are permitted. (j) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished. Isolation of the fuel cross feed lines behind the firewall may be required. (k) An alternative method of compliance or adjustment of the initial or repetitive compliance times that provides an equivalent level of safety may be approved by the Manager, 1801 Airport Road, Room 100, Wichita, Kansas 67209. (1) The request shall be forwarded through an appropriate FAA Maintenance Inspector, who may add comments and then send it to the Manager, Wichita Aircraft Certification Office. (2) Alternative methods of compliance approved in accordance with AD 75-23-08 R5 are not considered approved as alternative methods of compliance for this AD.

Note 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Wichita Aircraft Certification Office.

(l) Information related to this AD may be examined at the FAA, Central Region, Office of the Regional Counsel, Room 1558, 601 E. 12th Street, Kansas City, Missouri 64106. (m) This amendment supersedes AD 75-23-08 R5, Amendment 39-5451.

Appendix to Docket No. 97-CE-67-AD--Visual Inspection

(a) Cleaning

In order to properly inspect the exhaust system, components must be clean and free of oil, grease, etc. If required, clean as follows: (1) Spray engine exhaust components with a suitable solvent (such as Stoddard Solvent), allow to drain, and wipe dry with a clean cloth.

WARNING NEVER USE HIGHLY FLAMMABLE SOLVENTS ON ENGINE EXHAUST SYSTEMS. NEVER USE A WIRE BRUSH OR ABRASIVES TO CLEAN EXHAUST SYSTEMS OR MARK ON THE SYSTEM WITH LEAD PENCILS.

(2) Remove the heat shields from the turbocharger in accordance with the heat shield removal procedures in the appropriate Cessna Aircraft Service Manual. (3) Remove shields around the exhaust bellows or slip joints, multi-segment ``V'' band clamps at joints, and other items that might hinder the inspection of the system. Removal of the ``V'' band clamps may not be necessary. (4) Using crocus cloth, polish any suspect surfaces to verify that no cracks or pinholes exist in the material. Replace or repair any part where cracks or pinholes exist.

(b) Visual Inspection of Complete System

Note 1. Conduct this inspection when the engine is cool.

(1) Visually inspect exhaust stacks for burned areas, cracks, bulges, and looseness. Make sure the attach bolts are properly torqued, in accordance with the appropriate Cessna Aircraft Service Manual.

Note 2. During this inspection, pay special attention to the condition of the bellows and welded areas along the seams; the welded areas around the bellows; and the welded seams around the exhaust system components.

(2) Visually inspect the flexible connection between the waste- gate and overboard duct (when applicable) for cracks and security. (3) Visually inspect the exhaust joint springs for correct compression. If the joint is disturbed or if the springs are obviously loose or frozen, proceed with the following inspection (see Figure 1 of this Appendix). (i) Before removal of the exhaust joint springs, measure the installed length of each spring, and replace the springs compressed to less than .45 inch. (ii) Remove all the springs and measure the free length. Replace any spring having a free length of less than .57 inch.

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Note 3. Add AN960-10 washers under the head of the joint bolts as required to obtain the correct dimension. During installation, the joint bolts should be tightened gradually and spring length checked frequently to prevent over-compression of the springs.

(iii) Reinstall the springs and measure the installed length. The length must be .51 inch (+.00, -.03 inch). (4) If installed, visually inspect the slip joint(s) for bulges beyond the normal manufacturing irregularities of .03 inches and/or cracks. If any bulges and/or cracks are present, replace the bulged or cracked slip joint(s). (Refer to the appropriate Cessna Aircraft Service Manual) (See Figure 2 of this Appendix).

(c) Inspection of the Multi-Segment ``V'' Band Clamp(s) (Between Engine and Turbocharger)

(1) Using crocus cloth, clean the outer band of the multi- segment ``V'' band clamp(s). Pay particular attention to the spot weld area on the clamp(s). (2) With the clamp(s) properly torqued, progress to the following actions: (i) Visually inspect the outer band in the area of the spot weld for cracks (see Figure 3 of this Appendix). If cracks are found, replace the clamp(s) with new multi-segment ``V'' band clamp(s). (ii) Visually inspect the corner radii of the clamp inner segments for cracks (see Figure 3 of this Appendix). This inspection requires careful use of artificial light and inspection mirrors. (iii) Visually inspect the flatness of the outer band, especially within 2 inches of the spot welded tabs that retain the T-bolt fastener. This can be done by placing a straight edge across the flat part of the outer band as shown in Figure 4 of this Appendix, then check the gap between the straight edge and the outer band. This gap should be less than 0.062 inch. If deformation exceeds the 0.062-inch limit, replace the clamp(s) with new multi- segment clamp(s). (See Figure 3 of this Appendix). See Cessna maintenance manual(s) and revisions for correct installation procedures. (iv) Visually inspect the one-piece ``V'' band clamp (overboard exhaust to turbocharger) with a light and mirror, in the area of the clamp surfaces adjacent to the intersection of the ``V'' apex and bolt clips, and the entire length of the ``V'' apex of the clamp for signs of cracks or fractures. If cracks or fractures are visible, replace the clamp (see Figure 5 of this Appendix). See Cessna service manual(s) and revisions for correct installation procedures

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Inspection of the Exhaust System AFT of the Slip Joints

(a) Remove all top and bottom engine cowlings, as well as the under-nacelle inspection panels (on aircraft so-equipped). Remove the nacelle-mounted induction air filter canister, slip-joint heat shields, turbocharger heat shields, and any other readily-removable components that facilitate a better view of the exhaust system aft of the slip joints. (b) Visually inspect each elbow pipe that runs from the slip joint to the wye duct. Carefully inspect the hard-to-see areas where the manifold passes through the canted bulkhead, beneath the clamp- on heat shields, and around the flange and V-band clamp, where it joins the wye. Use a flashlight and mirror to inspect the areas that cannot be seen directly. (1) Look for evidence of exhaust stains, bulges, cracks, or pinholes. (2) Exhaust stains or evidence of heat-induced corrosion on any portion of the engine mount beams or canted bulkhead should be grounds for removing the elbow pipe for closer inspection. (3) Inspect for cracks, bulges, pinholes, or corrosion on the elbow (manifold) pipe, and if any of this damage is found, replace the elbow pipe. (c) Visually inspect each wye duct beneath the turbo charger for leakage, stains, cracks, or pinholes, and, if damaged, repair or replace. Carefully inspect the hard-to-see area between the duct and firewall. (1) Carefully inspect the turbo-charger and waste-gate flanges and welded seams between the ducts and the firewall for evidence of exhaust stains on the wye or the firewall, bulges, cracks, or pinholes. (2) If exhaust stains, bulges, cracks or pinholes are found, repair or replace the damaged part.

Pressure Test

(a) Pressurize the exhaust system with air regulated to 20 PSI or below. (b) Apply this air pressure to the tailpipe. Fabricate shop fixtures as required to accomplish this. (c) Seal off the waste-gate pipe. (d) Check the tailpipe, elbow pipes and the wye duct for leaks by spraying leak check fluid (bubbling) on these parts and looking for the appearance of bubbles. Some air leakage is normal at the joints and flanges, but none should be seen anywhere else. (e) Pay special attention to any weld repairs, and various hard- to-see areas described previously. (f) If the tailpipes, elbow pipes, or the wye ducts fail the pressure test, repair or replace the distressed component.

Issued in Kansas City, Missouri, on June 25, 1999. Michael Gallagher, Manager, Small Airplane Directorate, Aircraft Certification Service. [FR Doc. 99-16752 Filed 7-2-99; 8:45 am] BILLING CODE 4910-13-U