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AOPA response to Hartzell ADAOPA response to Hartzell AD

Federal Aviation Administration
New England Region
Office of the Assistant Chief Counsel
Attn: Rules Docket No. 96-ANE-40
12 New England Executive Park
Burlington, MA 01803-5299


The Aircraft Owners and Pilots Association (AOPA), representing the aviation interests of 340,000 pilots and aircraft owners, submits the following comments to the Hartzell Propeller Airworthiness Directive (AD) 97-18-02. This AD will have a significant economic impact on a group of owners who, in many instances, are most sensitive to any additional operating costs. This is due in large measure to the fact that this propeller AD affects many of the oldest and least expensive aircraft in the general aviation fleet. While it is understood that many aspects of AD 97-18-02 are based on significant adverse service history, there are several provisions contained within the AD that lack any specific justification or supporting data. Additionally, given the tremendous impact this AD will have on operating costs for these aircraft, AOPA urges the Federal Aviation Administration (FAA) to explore every avenue for reducing the compliance costs associated with this AD for operators of specific aircraft where possible.

AOPA is very concerned that the FAA has done little to justify the various provisions of this AD in the “Supplementary Information” section of the Federal Register notice. Reference has been made to cracks and failures of the propeller blade shanks, clamps, and hubs, but no specific information on the failure modes or time in service was provided by the FAA. Most notably, there is no information provided on which to judge the efficacy of the initial and repetitive compliance times established by the AD. AOPA has urged the FAA New England Region to include more useful data in the AD preamble on many occasions; however, we feel that this urging is falling on deaf ears. It often appears to the public that the FAA is trying to “slip one past” the general aviation community, when in fact the data exists but is simply deemed to be irrelevant or too technical for public consumption. Many needless negative public comments are generated as a result of the FAA’s failure to fully inform the general aviation community of the full scope of a given airworthiness problem. In our view, the FAA has a responsibility to justify its actions in imposing additional significant operating costs on aircraft owners by providing comprehensive background information on which the public can base its opinion.

AOPA has conducted an extensive examination of publicly available data related to Hartzell steel hub propellers, uncovering a large number of reported cracks or failures of the blade shanks and clamps. Consequently, AOPA agrees with the FAA that many provisions of this AD are justified. However, this failure information does not present an explanation of how the FAA arrived at the extremely burdensome repetitive compliance times required by AD 97-18-02. The data contained in the service and difficulty reports for these propellers does not contain much time-in-service information, so the public cannot determine on what basis the AD compliance times were established. In our view, this is the FAA’s responsibility, and we urge the FAA to publish this highly relevant information for public consumption, analysis, and future comment.

In the course of our research, AOPA could find no justification or data to support the 60-month repetitive inspection requirements outlined in this AD. AOPA has approached both the FAA and Hartzell seeking the data used to support this requirement, and there appears to be none available. In fact, the original draft Hartzell Service Bulletin submitted for FAA approval did not contain this provision at all, indicating that it was likely added by the FAA late in the development process. The decision to include this repetitive calendar time requirement appears to have no basis in fact or data, but rather seems to be an attempt to advance some unrelated agendas widely known to exist within the FAA Propeller Directorate. The stress and fatigue cracks being addressed by this AD are purely a function of design and cyclical stress and, therefore, have nothing to do with calendar time. If the FAA wishes to issue an AD addressing corrosion or other issues that are predicated largely on calendar time, we may then reexamine this issue. In the meantime, AOPA must insist that the repetitive calendar time inspection requirements be removed from this AD entirely.

Further, our research of the supporting data for this AD found no evidence of a chronic problem with blade bore corrosion other than the single blade separation reported by the FAA. It is our understanding that the inspection called out in AD 97-18-02 has never been a part of the Hartzell service or overhaul instructions and thus has likely never been accomplished in the 40-year history of these propellers. AOPA believes that based on the single failure and the fact that there has not been any requirement to inspect this area of the propeller in the past, it is probably a very good idea to remove the bushing and conduct the required inspection on a one-time basis under the AD. However, given that these propellers have gone nearly 40 years without attention before showing signs of a corrosion problem in this area, AOPA does not believe there is sufficient justification for requiring this inspection on a repetitive basis either in operating hours or calendar time. The fact that Hartzell has incorporated the required inspection in its overhaul manuals will ensure that the inspection is carried out in the future at normal maintenance intervals and well within any potential failure mode. Based on this, AOPA urges the FAA to change the blade bore corrosion inspection to a one-time inspection only with follow-up inspections to be conducted at overhaul.

The cost associated with repetitively complying with AD 97-18-02 is truly staggering to owners of older general aviation aircraft. AOPA is aware of one owner who has already complied with the AD at a cost of $3,800 per propeller. Unfortunately for this individual, the aircraft in question was a twin, meaning that the total initial compliance cost was $7,600. These propellers did not exhibit corrosion or cracks and only normal consumable parts were required to be replaced, indicating that this could well reflect the minimum cost of complying with AD 97-18-02 every 250 hours. Given these figures, the hourly cost of operating any aircraft with a subject Hartzell propeller installed would increase by a minimum of 25 percent simply as a result of this one AD.

Given that such dramatic cost implications are associated with this AD, AOPA finds it completely unacceptable that no economic impact data was presented in the Federal Register by the FAA. This absence of cost analysis, combined with the relatively thin presentation of the service history of these propellers, gives the public a very negative impression of the entire proposal and has contributed to a stronger than normal series of objections to this AD. Again, we reiterate that it is the FAA’s responsibility to publicly justify its actions, even matters affecting safety.

Because the economic impact of this AD is so severe and would reoccur with such frequency, AOPA is strongly urging the FAA and Hartzell to carefully examine all possible means of reducing the burden on owners with unique aircraft applications or usages where possible. For example, the Twin Bonanza Society has developed an analysis that indicates the potential for significantly less stress on Twin Bonanza propellers. This is due in large measure to the propeller installation on a geared engine. At a minimum, this data appears to argue in favor of longer compliance times, and perhaps even more. AOPA would encourage the FAA and Hartzell to consider data such as this very carefully with an eye toward reducing the burden of this AD on operators where there are demonstrated operational differences that distinguish certain aircraft from the fleet as a whole.

AD 97-18-02, as currently written, is one of the most burdensome ADs to come along in a very long time, both from the viewpoint of economics and aircraft downtime. Worst of all, it is repetitive without end. AOPA is very concerned that there is presently no terminating action to this AD, and no distinction made between relatively new propellers and those that are 40 years old. Every single propeller will be caught in the cycle of teardown inspections every 250 hours of operation unless something is done quickly. In our view, the FAA and Hartzell need to work together with all possible haste to develop some form of terminating action for this AD. We believe that if this is not accomplished very soon, many of these older aircraft will be grounded or relegated to mere collectors’ items due to the very high cost of operation.

We thank you in advance for your time and consideration and stand ready to assist the FAA and Hartzell in addressing our concerns.


Douglas C. Macnair
Aviation Standards

October 24, 1997

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