### FINAL **REGULATORY EVALUATION**

**DAMAGE TOLERANCE AND FATIGUE EVALUATION OF**  **COMPOSITE ROTORCRAFT STRUCTURE (14 CFR Parts 27**  **.573 and 29**  **.573 )** 

OFFICE OF AVIAT ION POLICY AND PLANS

Economic Analysis Division George A. Euring, Jr. Ju ne, 20 1 1i 

### TABLE OF CONTENTS
Page I. Introduction...................................................................................... 1 II. Background....................................................................................... 2 III. Benefits

........................................................................................... 4 IV
. Costs

... .......................................................................................... .5 V. Benefit Cost Co mparison...................................................................... 1 11



### DAMAGE TOLERANCE AND FATIGUE EVALUATION OF COMPOSITE

**ROTORCRAFT STRUCTURE**

**I. INTRODUCTION**  This regulatory

evaluation estimates the benefits and costs , $39 2, 000 in present value, of a new Federal Aviation Regulatio n. The new rule will 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 Evaluation for Composite Structure. The current regulations were written for metallic structu re and do not provide adequate certification standards for composite materials and structures. This new rule will add airworthiness standards to evaluate the fatigue strength and residual static strength of composite rotorcraft structure s usi ng a damage tolerance evaluation and, if that is impractical, a fatigue evaluation. This rule will also add safety requirements for composite rotorcraft structure that address advances in composite structures technology

. In addition to improving the level of safety for all principal structural elements (PSE s ), the final rule will also increase safety by leading to a more harmonized international standard with the European Aviation Safety Agency (EASA)

. The proposed rule was published as an NPRM (Notice of Proposed Rulemaking) on January 6, 2009. O ne economic comment was received during the comment period. As a result of the comment , we provide an upper bound for the compliance costs.2

**II. BACKGROUND**  **A. Statement of the Problem**  The current regulations do not p rovide adequate certification standards for composite materials and structures. Certification has been based on a broad interpretation of the metallic fatigue substantiation and the design and construction airworthiness standards. The T ype 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 rotorcraft structures, certification, and se rvice experiences for composite rotorcraft structures over the last twenty - five ye ars has created a need to reconsider the current regulations for damage tolerance and fatigue evaluation. To this end, an Aviation Rulemaking Advisory Committee (ARAC) worki ng group (WG) was chartered to study the problems and offer recommendations for rotorcraft composite structure minimum safety standards. **B. History**  The international ARAC WG that assembled in 2000 consisted of industry practitioners, regulatory

officials , and technical 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 industry experience with composite structures. The team included members familiar with the different rotorcraft structures, including airframe, main and tail rotor drive sy stems, main and tail rotor blades and hubs, rotor controls, fixed and movable control surfaces, and transmission mountings. Both Part 27 (normal) and 29 (transport) category rotorcraft manufacturers had representatives on the team. Such a balanced team was needed to develop recommendations that consider the unique technical issues and design3

characteristics for composites used in the different rotorcraft structures. The ARAC WG considered alternatives and determined that rulemaking action should be recommended. The WG felt that taking no action would result in continued confusion among and within manufacturers and authoritie s. Relying on advisory material only , as in the past, did not alway s remove the need for special conditions, and advisory material was not enforceable. The only existing rule for damage tolerance and fatigue evaluation of structures using composite materials is § 23.573 (a)

. Much of this Part 23 rule has details for composite airframe structures subjected to relativel y low numbers of fatigue cycles. Because some critical rotorcraft structures experience a high number of fatigue cycles, the ARAC WG felt the Part 23 airworthiness standards were not acceptable for the complete range of composite rotorcraft structures. The ARAC WG’s effort resulted in recommendations for new regulatory standards and standardized means of compliance that allows for innovati on and changes in technology

. To
carry out the recommendations, the WG proposed regulations, §§ 27.573 and 29.573, specific to composite rotorcraft structures
. The WG concurrently developed advisory material to support the proposed regulations. In revi ewing experiences with composite rotorcraft structures, it became clear that different safety concerns existed , depending on the specific rotorcraft application. Many of the differences related to fatigue and accidental damage threats, design detail, and critical load cases. For example, rotor blades, which are dyn amicall y loaded b y 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.4

**C. The Need for Regulatory Change**  New composite rotorcraft structure standards are needed because:

 Existing regulations, §§ 27.571 and 29.571, do not adequatel y describe the fatigue certification requirements for composite rotorcraft structures . The lack of regulatory requirements has led to inconsistent interpretations from one rotorcraft certification project to another, resulting in different burdens on industry to substantiate the safety of the ir composite rotorcraft structures . As discussed previousl y, some special conditions have been required to establish adequate and appropriate safety standards.

 Some applicants state that the lack of a separate composite rotorcraft structure rule has result ed 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 integrate and reflect the rotorcraft industry ’s historical experience in carrying out certification of composite rotorcraft structures
.

 There have been significant changes in composite technology since the current rule and the o riginal advisory

material were written. In recent ye ars there have been changes in design, anal ys is, testing, manufacturing, maintenance techniques, and maintenance procedures. The new regulations and advisory materials will account for these significant c hanges. **III .**  **Benefits** This final rule sy stematizes past FAA and industry practice regarding the use of composites on rotorcraft, including special conditions and advisory circulars

. Although we anticipate both cost savings and improved safety in consequ ence of the proposed rationalization of inspection and replacement schedules, we are unable to quantify these benefits. Nevertheless,5

we believe that the qualitative ly estimated benefits are real and significant and exceed the rule’s costs
. We presented this benefit argument in the NPRM, asked for comments, received none. Therefore, we did not change the determination that benefits exceed costs.

**IV .**  **COSTS A.**  **Introduction** The final rule will require rotorcraft manufacturers and operators to take additional actions

. Manufacturers will be required to : 1) perform a more thorough threat assessment, 2) perform a more rigorous residual strength assessment, and 3) establish inspection intervals

. Operators will be required to conduct additional inspect ions if the final rule result s in a more rigorous inspection schedule than the operator is currentl y following

. However, we believe that the schedule of an y i nspection s required would largel y coincide with that of metallic structure inspections

. **B. Manu**  **facturers Costs** The rotorcraft manufacturers currentl y perform a threat assessment and a resid ual strength assessment, but the se would become more robust under the proposed rule. The current metallics requirements mandate the establishment by manufacturer s of inspection intervals **or** retirement times. This final composites rule mandates both retirement times **and** inspection intervals that must be included in the airworthiness limitation section of the Instructions for Continued Airworthiness (I CA)

.6

It is current practice for the rotorcraft manufacturers to establish retirement times fo r composite structures. Therefore, this final rule does not impose any incremental costs associated with establishing retirement times

. It will , however, impose the costs o f establishing inspection intervals. Relying on information from industry representatives on the ARAC Working Group, the FAA estimates that the average additional cost for Part 29 aircraft manufacturers to perform a more thorough threat assessment will b e $100,000 per certification; the average additional cost to perform the more rigorous residual strength assessment proposed b y this rule will be an additional $50,000 per certification; and putting both retirement times and inspection intervals in the air worthiness limitation section of the Instructions for Continued Airworthiness will cost , on average , an additional $54,000 per certification. These costs 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 representatives, the FAA also estimates that over the next 27 ye ars, Part 29 rotorcraft structures will comprise approximately 50% metallic parts and 50% c omposite p arts. Hence, the additional Part 29 certification cost under this final rule will be $50,000 for a threat 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 i nspection intervals and retirement times in the airworthiness limitation section ($54,000 * 0.5 = $27,000). Therefore, the FAA estimates that the average total certification cost per new Part 29 type certification will be $102,000 ($50,000 + $25,000 + $27 ,000 = $102,000). Using information received from industry representatives, the FAA estimates that over the next 27 years, p art 27 rotorcraft structures will comprise approximately 80% metallic parts7

and 20% composite parts. Using information from indus try representatives, the FAA estimates that there are no additional costs to Part 27 manufacturers for the threat assessment and the residual strength assessment. Putting both retirement times and inspection intervals in the airworthiness limitation secti on will cost , on average , an additional $48,000 per Part 27 certification. Hence, the average total certification cost per new Part 27 ty pe certification under this proposed rule would be $9,600 ($48,000 * 0.2 = $9,600). Table C 1 below shows a summary of the average cost per certification. Using information from industry representatives, the FAA estimates that there would be 2 new Part 29 type certifications every 10 ye ars, and 3.5 new Part 27 type certifications every 10 ye ars. We front

- load certificati on to the first year of each new decade. Therefore, we assume there will be 2 new part 29 and 3.5 new part 27 helicopter certificates in the first, eleventh, and twenty
- first years of the anal ys is period. This results in a total of 6 new part 29 and 10.5 part 27 helicopter type certificates during the 27 ye ar analy sis period. At an average Part 29 new certification cost of $102,000, the expected Part 29 cost is $612,000 (6*$102,000). With the Part 27 new certification average cost increase of $9,600, the expected Part 27 compliance cost is $100,800 (10.5*$9,600) . The sum of Part 27 and Part 29 compliance cost equals the total compliance cost of $712,800 or $392,000 in present value.89

**C. Operators Costs**  Operators costs will consist of costs for an y inspections in excess of what they are currentl y performing. It is anticipated that there will be no additional inspection costs imposed as a result of this final rule. The minutes of the Rotorcraft Is sues Group of the Aviation Rulemaking Advisory

Committee for the meeting of February 15, 2002, held at Orlando, Florida , contained a report of the Working Group on Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structure. Part of this report states that “Industry 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 document and understand it and know what to do.” Operators have alway s performed inspections on their helicopters. We do not expe ct 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 ty pic all y are life

- limited (needing to be replaced at specified intervals) , while composite blades have no life limit and are ty picall y replaced because of condition. This difference can result in major savings to helicopter operators. We received no comment s regarding this conclusion. Therefore we accept our finding of no additional costs to operators.10

**D. Total Costs**  T he total costs of this final rule are the total certification costs of the final rule over the 27 ye ar anal ys is period and are e stimated t o be about $713,000 in undisc ounted costs or about $392,000 in discounted costs as shown in Table C2. Based on a commenter cost estimate of 12,000 hours and an estimated $86, the burdened hourly rate for an aeronautical engineer , we estimate the total nom inal dollar estimate to be $1,032,000 (12,000*$86) , or ($567,000 in present value). The originally

- provided ARAC data provides the lower bound cost estimate and by accepting the commenter’s information we have an upper bound cost estimate. Over 27 ye ars the present value difference between these estimates is $175,000 . Based on this information we estimate the nominal total compliance costs of this final rule to be between $713,000 and $1,032,000 and the present value total compliance costs to be between $392,000 and $567,000.11

**V .**  **Benefit -**  **Cost Comparison** 

This final rule sy stematizes past FAA and industry practice regarding the use of composites on rotorcraft, including special conditions and advisory circulars Although we anticipate both cost savi ngs and improved safety in consequence of the proposed rationalization of testing, inspection and replacement schedules, we are unable to quantify these benefits.12

Nevertheless, based on industry

- provided data we believe that this final rule, will yield be nefits exceeding the estimated costs
.