### INITIAL REGULATORY EVALUATION, INITIAL REGULATORY FLEXIB ILITY DETERMINATION, INTERNATIONAL TRADE IMPACT ANALYSIS, AND UNFUNDED MANDATE ASSESSMENT

DAMAGE TOLERANCE AND FA TIGUE EVALUATION OF COMPOSITE ROTORCRAFT STRUCTURE (14 CFR Parts 27.573 and 29.573)

OFFICE OF AVIATION POLICY AND PLANS AIRCRAFT REGULATORY ANALYSIS BRANCH, APO-320 George A. Euring, Jr.

December 4, 2009

### TABLE OF CONTENTS

Page

I. Introduction......................................................................................1 II. Background.......................................................................................2 III. Benefits...........................................................................................4 IV. Costs..............................................................................................5 V. Benefit Cost Comparison......................................................................11

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### DAMAGE TOLERANCE AND FATIGUE EVALUATION OF COMPOSITE ROTORCRAFT STRUCTURE

I. INTRODUCTION

This regulatory evaluation estimates the bene fits and costs, $390,000 in present value, of a proposed new Federal Aviation Regulation. Th e proposed rule would amend Parts 27 and 29 of Title 14, Code of Federal Regulations (14 CFR) by adding new parts 27.573 and 29.573 Damage Tolerance and Fatigue Evalua tion for Composite Structure. The current regulations were written for me tallic structure and do not provide adequate certification standards for composite materials and structures. This proposed rule would add ai rworthiness standards to evaluate the fa tigue strength and residual static strength of composite rotorcraft structures using a damage tolerance evaluation and, if that is impractical, a fa tigue evaluation. This proposal would also add safety requirements for composite rotorcraft structur e that address advances in com posite structures technology. In addition to improving the level of safety for a ll principal structural elements (PSEs), the proposed rule would also increase safety by lead ing to a more harmonized international standard with the European Aviation Safety Agency (EASA).

1II. BACKGROUND

A. Statement of the Problem The current regulations do not provide ade quate certification standards for composite materials and structures. Certification has been based on a broad interpretation of the metallic fatigue substantiation and the design and constr uction airworthiness standards. The Type Certification solutions sought for composite and metal structures are different. As a result, special conditions were necessary for some certification projects using composite structures. The increased use of composites in rotorc raft structures, certi fication, and service experiences for composite rotorcraft structures ov er the last twenty-five years has created a need to reconsider the current regulati ons for damage tolerance and fatigue evaluation. To this end, an Aviation Rulemaking Advisory Committee (ARAC) working group (WG) was chartered to study the problems and offer recommendations for ro torcraft composite structure minimum safety

standards. B. History

The international ARAC WG that assembled in 2000 consisted of industry practitioners, regulatory officials, and techni cal specialists, each with unique experiences with composite applications. The two co-chairs, one from a U. S. manufacturer and the other from a European manufacturer, each had many years of rotorcraft i ndustry experience with composite structures. The team included members familiar with the different rotorcraft structures, including airframe, main and tail rotor drive systems, main and tail rotor blades and hubs, rotor controls, fixed and

movable control surf aces, and transmission mountings. Both Part 27 (normal) and 29 (transport) category rotorcraft manufacturers had representativ es on the team. Such a balanced team was needed to develop recommendations that cons ider the unique techni cal issues and design

2characteristics for composites used in th e different rotorcra ft structures.

The ARAC WG considered alternatives and determined that rulemaking action should be recommended. The WG felt that taking no acti on would result in continued confusion among and within manufacturers and authorities. Relyi ng on advisory material only, as in the past, did not always remove the need for special conditions , and advisory material was not enforceable. The only existing rule for damage tolerance and fa tigue evaluation of stru ctures using composite materials is § 23.573 (a). Much of this Part 23 ru le has details for composite airframe structures subjected to relatively low numbers of fatigue cycl es. Because some critical rotorcraft structures experience a high number of fatigue cycles, th e ARAC WG felt the Pa rt 23 airworthiness standards were not acceptable for the complete range of composite rotorcraft structures.

The ARAC WG’s effort resulted in recomm endations for new regul atory standards and standardized means of complian ce that allows for innovation a nd changes in technology. To carry out the recommendations, the WG pr oposed regulations, §§ 27.573 and 29.573, specific to composite rotorcraft structures. The WG concu rrently developed adviso ry material to support the proposed regulations. In reviewing experiences with composite rotorcraft structures, it became clear that different safety concerns existed, depending on th e specific rotorcraft application. Many of the differences related to fatigue and accidental damage threats, design detail, a nd critical load cases. For example, rotor blades, which are dynamically loaded by predominantly centrifugal forces,

are different from an airframe structure with significant compressive loads. Because of this variability, the ARAC WG developed a general rule applicable to all types of composite

rotorcraft structures.

3C. The Need for Regulatory Change New composite rotorcraft structur e standards are needed because:

• Existing regulations, §§ 27.571 and 29.571, do not adequately describe the fatigue certification requirements for composite rotorc raft structures. The lack of regulatory requirements has led to inconsistent interpretatio ns from one rotorcraft certification project to another, resulting in different bu rdens on industry to substantiate the safety of their composite

rotorcraft structures. As discu ssed previously, some special cond itions have been required to establish adequate and appr opriate safety standards.

• Some applicants state that the lack of a sepa rate composite rotorcraft structure rule has resulted in confusion, because neither the current rules nor the various advisory materials provide clear and complete guidance for certification of composite rotorcraft structures. New rules and

AC material are intended to alleviate this problem.

• The new rules and advisory materials will inte grate and reflect the rotorcraft industry’s historical experience in carry ing out certificati on of composite rotorcraft structures.

• There have been significant changes in co mposite technology since the current rule and the original advisory materi al were written. In recent years there have been changes in design, analysis, testing, manuf acturing, maintenance techniques, and maintenance procedures. The new proposed regulations and advisory materi als will account for these significant changes.

III. Benefits This proposed rule systematizes past FAA and industry practice regarding the use of composites on rotorcraft, including special conditions and advisory circular s Although we anticipate both cost savings and improved safety in consequence of the proposed rationalization of inspection

4and replacement schedules, we are unable to quan tify these benefits. Nevertheless, we believe that the qualitatively estimated benefits are real and significant and exceed the rule’s costs.

IV. COSTS

A. Introduction The proposed rule would require rotorcraft ma nufacturers and operators to take additional

actions. Manufacturers would be required to: 1) perform a more thorough threat assessment, 2) perform a more rigorous resi dual strength assessment,

and 3) establish inspection intervals. Operators would be required to conduct additio nal inspections if the proposed rule results in a more rigorous inspection schedule than the operator is currently following. However, we believe that the schedule of any inspections requir ed would largely coincide with that of metallic structure inspections.

B. Manufacturers Costs The rotorcraft manufacturers currently perf orm a threat assessment and a residual strength assessment, but these would become more robust under the proposed rule. The current metallics requirements mandate the establishment by manufacturers of inspection intervals or retirement times. This proposed composites rule mandates both retirement times and inspection

intervals that must be included in the airworth iness limitation section of the Instructions for Continued Airworthiness (ICA). It is current practice for the rotorcraft manufacturers to establish retirement times for composite structures. Therefor e, this proposed rule does not impose any incremental costs

5associated with establishing retirement times. It would, however, impose the costs of establishing inspection intervals. Relying on information from industry repr esentatives on the AR AC Working Group, the FAA estimates that the average additional cost for Part 29 aircraft manufacturers to perform a more thorough threat assessment would be $100,000 pe r certification; the av erage additional cost to perform the more rigorous residual strength assessment proposed by this rule would be an additional $50,000 per certification; and putting both retirement time s and inspection intervals in

the airworthiness limitation section of the Instru ctions for Continued Airworthiness would cost, on average, an additional $54,000 per certification. These co sts are associated with certification of rotorcraft using all-composite parts in the certified categories and to vary in proportion to the share of composite parts. Using information received from industry repr esentatives, the FAA also estimates that over the next 27 years, Part 29 rotorcraft structures will comprise approximately 50% metallic parts and 50% composite parts. Hence, the ad ditional Part 29 certifi cation cost under this proposed rule would be $50,000 for a thre at assessment ($100,000 * 0.5 = $50,000), $25,000 for a residual strength assessment ($50,000 * 0.5 = $25,000), and $27,000 for putting both inspection intervals and retirement times in the airworthiness limitati on section ($54,000 * 0.5 = $27,000). Therefore, the FAA estimates that the av erage total certification cost per new Part 29 type certification would be $102,000 ($50,000 + $25,000 + $27,000 = $102,000). Using information received from industry repr esentatives, the FAA estimates that over the next 27 years, part 27 rotorcraft structur es will comprise approximately 80% metallic parts and 20% composite parts. Using information fr om industry representatives, the FAA estimates

that there are no additional costs to Part 27 manufacturers for the threat assessment and the

6residual strength assessment. Putting both retirement times and inspection intervals in the airworthiness limitation section would cost, on average, an additional $48,000 per Part 27 certification. Hence, the averag e total certificatio n cost per new Part 27 type certification under this proposed rule would be $9,600 ($48,000 * 0.2 = $9,600). Table C1 below shows a summary of the average cost per certification. Using information from industry representative s, the FAA estimates that there would be 2 new Part 29 type certifications every 10 years, and 3.5 new Part 27 type certifications every 10 years. We front-load certification to the first year of each new decade. Therefore, we assume there would be 2 new part 29 and 3.5 new part 27 he licopter certificates in the first, eleventh, and twenty-first years of the analysis period. This results in a to tal of 6 new part 29 and 10.5 part 27 helicopter type certificat es during the 27 year analysis period. At an average Part 29 new certification co st of $102,000, the expected Part 29 cost is $612,000 (6*$102,000). With the Part 27 new certific ation average cost increase of $9,600, the expected Part 27 compliance cost is $100,800. The sum of Part 27 and Part 29 compliance cost equals the total compliance cost of $712,800 or $392,000 in present value.

78C. Operators Costs Operators costs would consist of costs for a ny inspections in excess of what they are currently performing. It is anti cipated that there would be no a dditional inspection costs imposed as a result of this proposed rule . The minutes of the Rotorcraft Issues Group of the Aviation Rulemaking Advisory Committee for the meeting of February 15, 2002, held at Orlando, Florida, contained a report of the Work ing Group on Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structure. Part of this report states that “Indus try has indicated there should be no cost impact as a result of the new rule and new advisory circular material. They have also stated they have read the docume nt and understand it and know what to do.” Operators have always performed inspections on their helicopters. We do not expect composite parts to require more inspections, unless the composite part has a longer life than the metallic part. For a part with a longer life, the initial inspection is likely to occur later than the same part made of metal. A review of proprietary information from a helicopter manufacturer that produces both metal and composite helicopters indicates that composite parts have maintenance requirements the same as or lower than those of metal parts. Of special interest is that metal rotor blades typically are life-limited (needing to be replaced at specified intervals), while composite blades have no life limit and are typically replaced because of condition. This difference can result in major savings to helicopter operators. The FAA requests comments regarding our beli ef that composite part inspection costs will not be higher than those fo r corresponding metallic parts.

9D. Total Costs The total costs of this proposed rule are the total certification co sts of the proposed rule over the 27 year analysis period and are estimated to be about $713,000 in undiscounted costs or about $392,000 in discounted costs as shown in Table C2.

10V. Benefit-Cost Comparison This proposed rule systematizes past FAA and industry practice regarding the use of composites on rotorcraft, including special condi tions and advisory circulars Although we anticipate both cost savings and improved safety in consequence of the proposed rationalization of testing, inspection and repla cement schedules, we are unable to quantify these benefits. Nevertheless, we believe that this rule,will yield benefits which, although estimated only qualitatively, will exceed the modest costs, to taling $392,000 in present value, which represents an annualized value of $32,700.

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