Airworthiness Directives; Cessna Aircraft Company 300 and 400 Series Airplanes

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]

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