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Regulatory Brief -- FAA proposed twin Cessna wingspar ADsRegulatory Brief -- FAA proposed twin Cessna wingspar ADs

September 3, 2003

Federal Aviation Administration
Central Region - Office of the Regional Counsel
ATTN: Rules Docket No. 2002-CE-05-AD
901 Locust - Room 506
Kansas City, MO 64106


The Aircraft Owners and Pilots Association (AOPA), on behalf of more than 400,000 pilots and aircraft owners, requests a 180-day extension to the comment period of proposed AD 2002-CE-05-AD. The proposed AD, intended to preclude wing failure due to undetected fatigue cracks, mandates inspection of wing spar caps for fatigue cracks and installation of a spar strap modification kit on each wing spar.

Preliminary research by aircraft type-clubs such as Cessna Pilots Association (CPA), and Twin Cessna Flyer, AOPA, and several interested owners and operators, has raised serious questions regarding the true scope and nature of fatigue cracks in the wing spar caps of twin Cessnas subject to this AD proposal. Very serious questions surround operating history and service condition of the few aircraft exhibiting spar cap fatigue cracks. Initial research has revealed damage history common to several of the aircraft referenced in the AD proposal.

Further, field application of the inspection and modification processes set forth in the proposed AD have raised serious doubt about the ability of mainstream general aviation service facilities to safely conduct the proposed AD's required maintenance actions. The highly technical nature of the proposed inspection method, and the precision required to install the proposed spar strap modification kit without degrading the integrity of the wing structure require highly skilled personnel and specialized equipment.

Initial analysis has also revealed that FAA may have very seriously underestimated the true cost of complying with the provisions of the proposed AD. Economic estimates from several maintenance facilities have indicated that conducting the proposed inspections and spar strap modifications would require a dedicated staff of four highly skilled mechanics nearly one full work-month to complete - at a cost of nearly $70,000 per aircraft!

An inventory of existing twin Cessna maintenance facilities has revealed that very few maintenance shops have the skills and equipment necessary to conduct the operations required by the proposed AD. A total of 779 401, 401A, 401B, 402, 402A, and 402B model aircraft are listed on the FAA aircraft registry. Industry estimates indicate that as few as 4-8 maintenance facilities in the country have the equipment and expertise necessary to safely conduct the operations required by the proposed AD - at the FAA estimated rate of one aircraft per 3-4 weeks, these facilities could complete only 96 aircraft per year. Assuming the number of capable maintenance facilities doubled during the first or second years - a service level that most in industry seriously doubt we may reach - a maximum of 338 aircraft may be completed at the FAA estimated rate of 3-4 weeks per aircraft.

Given the above, it is likely to take several years to comply with the provisions of the proposed AD! The resulting aircraft downtime (or loss of operational flexibility related to provisional aircraft operating limitations) will be devastating to owners and operators of affected aircraft, and will likely end the use of subject aircraft in a business or revenue generating capacity. Thus, the true economic implications of this proposal may be several orders of magnitude higher than FAA has estimated in the AD proposal.

AOPA, CPA, Twin Cessna Flyer, and several affected owners and operators continue to evaluate the FAA's proposal and search for alternatives. However, research to date has raised more questions than answers. Given the highly technical nature of the FAA's proposed action, the scarcity of facilities capable of safely conducting the compliance actions required by the proposed AD, the gross underestimation of the true economic impact of the proposed AD, and the dire safety implications of improperly installing the proposed spar strap modification kit, it is imperative that industry have ample opportunity to more thoroughly evaluate this issue.

Given the fact that the theoretical engineering analysis used to substantiate this AD proposal was developed by Cessna (using FAA funds) and completed nearly 7 years ago, and given the fact that there have been no reports of failures or other service issues related to fatigue cracks in spar caps of subject aircraft during that time, extending the comment period of this proposed AD should not compromise safety. Thus, AOPA respectfully requests that FAA grant the general aviation community an additional 180-days to generate appropriate data from the field to supplement the theoretical engineering analysis used to substantiate this AD proposal.

Thank you for your time and careful consideration in this matter - AOPA stands ready to assist the FAA in evaluating a more appropriate means to mitigate any safety concerns regarding the probability of fatigue cracks in spar caps of twin Cessna aircraft.


Andrew Werking
Associate Director
Regulatory and Certification Policy

cc: Michael Gallagher - Manager, FAA Small Airplane Directorate