FAA issues long-awaited twin Cessna exhaust AD - AOPA Comments

April 12, 2000

Federal Aviation Administration
Central Region � Office of the Regional Counsel
Attn: Rules Docket No. 97-CE-67-AD
601 East 12 th St., Room 1558
Kansas City, MO 64106

Gentlemen,

The Aircraft Owners and Pilots Association, representing the aviation interests of more than 355,000 pilots and aircraft owners, submits the following comments to Final Rule Airworthiness Directive AD-2000-01-16. The AD supercedes AD-75-23-08-R5 and implements new inspection procedures/compliance schedules for exhaust systems on turbocharged twin Cessna 300 and 400 series airplanes.

AOPA thanks the FAA for taking the industry�s comments into consideration when crafting the compliance actions and compliance schedule of this final rule AD. Further, AOPA is pleased that the FAA has acted upon the suggestions of members of the GA community and taken appropriate action to minimize the economic impact of the provisions of this AD. In keeping with this spirit of cooperative rulemaking, AOPA sincerely hopes and expects that the FAA will take one final step in clarifying and refining the actions required by this AD and incorporate the revisions proposed during this last round of industry comment.

Because of the technical nature of the issues surrounding this AD, AOPA has continued to rely upon the aircraft-specific technical knowledge of the Cessna Pilots Association (CPA) in the formulation of our comments. AOPA offers the following comments in order to clarify the requirements of AD-2000-01-16:

Figure 1 � Compliance Table - Column C � Actions

"Remove the tailpipes and visually inspect for any crack, corrosion, holes or distortion upon the accumulation of 5 years since installing a new or overhauled exhaust system or within the next 100 hours TIS after the effective date of this AD, whichever occurs later and thereafter at intervals not to exceed 12 calendar months."

According to the AD�s compliance schedule, the 12 month repetitive inspection would be required if any of the exhaust components were more than 5 years old. AOPA recognizes that the FAA has attempted to clarify this matter through the issuance of Special Airworthiness Information Bulletin (SAIB) No. CE-00-16. In the SAIB it states "NOTE: The words �exhaust system� in the Initial Compliance Time, column �c� of the chart should be interpreted as �exhaust tailpipe�". Such clarification renders the application of the 12 month repetitive inspection to tailpipes only.

AOPA is concerned that the present FAA clarification, contained only in an SAIB (an advisory document), has little or no regulatory significance. Further, two existing documents, each containing different "interpretations", may lead to confusion among individuals trying to comply with the provision of the AD. For the sake of clarity and simplicity, AOPA recommends that the FAA consolidate this clarification into the text of the AD.

Figure 1 � Compliance Table � column G � Actions

"Remove the exhaust system from the slip joints aft to all turbo-charger components."

There is considerable confusion as to what exactly the FAA means by "all turbo-charger" components. Does this include the tailpipe which is aft of the turbocharger? CPA and AOPA anticipate that it was the FAA�s intention to include all components from the slip joints to the turbocharger and the tailpipe. AOPA recommends that the FAA modify this section to more accurately reflect the true requirements of this provision.

Figure 1 � Compliance Table � column G � Repetitive Compliance Times

"Thereafter at intervals not to exceed 2,500 hours TIS or 12 years, whichever occurs first. These inspection intervals are established to coincide with regularly scheduled engine overhaul."

There is considerable confusion as to the meaning of this provision. AOPA recognizes that the FAA has attempted to clarify this matter through the issuance of Special Airworthiness Information Bulletin (SAIB) No. CE-00-16. In the SAIB the FAA has fully explained that compliance with this provision is only required upon the accumulation of 2,500 TIS or 12 years.

However, for the sake of clarity and simplicity, AOPA recommends that the FAA include this clarification in the compliance table of AD-2000-01-06.

Paragraph (a) � item (1) � Repairs required to be accomplished by an FAA approved exhaust repair facility

"Repairs: Required to be accomplished at an FAA-approved exhaust repair facility"

AOPA maintains that this requirement is much to general, and could therefore be interpreted to be applicable to all repairs conducted in accordance with this AD. AOPA sees no compelling need to require that airframe or other non-exhaust related repairs associated with this AD be completed exclusively at an FAA-approved exhaust repair facility. Consequently, AOPA recommends that the FAA clarify the language of this section and clearly specify that only repairs to exhaust system components must be conducted at FAA-approved exhaust repair facilities.

Paragraph (d) � item (1) - engine beam inspection

"If damage to the engine beams is found that exceeds 10 percent material thickness or there is evidence of overheating on the firewall beyond that which can be removed with �scotchbrite� or equivalent, prior to further flight, replace the firewall and the aluminum fuel lines behind the firewall."

As written, this section has been the cause of considerable confusion. It is unclear why the FAA would require replacement of a firewall based on damage to an engine beam. AOPA recommends that the FAA clarify the requirements of this section to more accurately reflect the need to replace all damaged components.

Note 6 � checking turbocharger wheel

"The FAA recommends checking the turbocharger wheel for ease of rotation any time the tailpipe is removed�The turbine wheel should continue to rotate for at least three seconds after spinning induced by fingers or a wooden tool."

It is commonly held that on a cool engine oil drag can be so substantial as to prevent even a healthy turbocharger from spinning for a full three seconds. It is likely that any turbocharger with more than a few hours TIS will fail this test. Consequently, AOPA recommends that the FAA revise the language of note 6 to read: "Check the turbine wheel for freedom of rotation, and noticeable end-play or side-play, and signs of any contact between the turbine wheel and the scroll housing."

Conclusion

AOPA recognizes that the provisions of AD-2000-01-06 are a vast improvement over those contained in the FAA�s original AD proposal, substantially reducing the economic burden upon affected aircraft owners. AOPA offers the above listed comments as a final step in making this AD clearer and more concise.

AOPA appreciates that the FAA has afforded the public one final opportunity to help the FAA in clarifying the provisions of this AD. The promulgation of this AD, although contentious at times, has proven to be an excellent example of how general aviation owners organizations, aircraft type-clubs, and the GA community can aid the FAA in arriving at reasonable and affordable solutions to legitimate airworthiness concerns.

Thank you for your time and consideration in this matter. AOPA stands ready to assist the FAA in reconsidering the provisions of Final Rule AD 2000-01-06.

Respectfully,

Dennis E. Roberts
Vice President/Executive Director
Government and Technical Affairs