Petition for Exemption 

from 14 C.F.R. § 33.27(1)(6), 

Amendment 33·31 

A. Name, Address and Contact Information ot the Petitioner 

Tunde Oyinloye 

Airworthiness Engineer 

ML-52 

Rolls-Royce pic 

PO Box 31 

Derby 

DE24 8BJ 

England 

Tel (+44) 1332 249294 

Tunde.oyinloye@ rolls-royce. com 

B. Pertinent Section ot the Code of Federal Regulations 

I Rolls-Royce 

Rolls-Royce hereby petitions for an exemption from 14 C.F.R. § 33.27(1)(6). This exemption is 

requested for the HP shaft system only, for the Trent XWB engine models identified in Section C 

below. 

The pertinent provisions of 14 C.F.R. § 33.27 are: 

14 C.F.R. § 33.27 Turbine, compressor, fan, and turbosupercharger rotor overspeed. 

(f) Failure of a shaft section may be excluded from consideration in detennining the highest 

overspeed that would result from a complete loss of load on a turbine rotor if tha applicant: 

(6} Does not exclude the entire shaft. 

C. The Exemption Being Sought 

Rolls-Royce requests an exemption from 14 C.F.R. § 33.27(f}(6} for the HP shaft system or the 

following Trenl XWB engine models: 

Model 

Trent XWB-84 

Trent XWB-798 

Trent XWB-79 

Trent XWB-75 

Rating x 1 000 lbs. 

84 

79 

79 

75 

No exemption is sought for other shaft systems on these, or any other, engine models. The HP 

shaft system will comply with § 33.27, subject to the granling of the exemption from § 33.27(f)(6) 

requested herein. 

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Rolls-Royce seeks an exemption from § 33.27(f)(6} to exclude the entire HP shaft system from 

consideration in determining the highest overspeed that would result from a complete loss of load on 

a turbine rotor. As demonstrated in Section E below and in the substantiating report, the level of safety 

afforded by compliance with § 33.27 for the HP shaft system will be unaffected by the granting of an 

exemption from § 33.27(f)(6}. The FAA has previously determined that allowing disc burst speed to 

be less than 100% rotor terminal speed could result in a hazardous condition, and that to ensure that 

safety is not adversely affected because of an HP shaft failure, the HP turbine disc burst speed must 

be greater than the terminal speed. The FAA also determined that the data (field experience, design 

similarity, Failure Modes and Effects Analysis, and terminal speed methodology} previously provided 

by Rolls-Royce regarding other Trent engine models was sufficient to reduce from the 105% terminal 

speed requirement of 14 C. F. A. § 33.27 without adversely affecting safety. Rolls-Royce requests that 

the exemption from § 33.27(f}(6} be granted on the basis of Rolls-Royce's demonstration that for each of 

the listed Trent XWB-84K engine models the HP turbine disc burst speed is greater than 100% rotor 

terminal speed resulting from HP shaft system failure. 

In sum, Rolls-Royce is requesting this exemption because compliance with § 33.27 cannot be shown 

absent an exemption from § 33.27(f}(6). However, compliance can be shown, without adversely 

affecting safety to that required to meet § 33.27, if the exemption is granted. 

D. Statement of Public Interest 

Granting this exemption will promote and serve the public interest because: 

• The state-of-the-art engine models (and the HP shaft system} at issue in this petition 

represent the latest generation of engines and engine technology from the Trent engine 

family. The Trent line of engines has established an outstanding track record of 

performance and safety for over 41 years and more than 250 million service flight hours. 

Thus, the engine models and shaft system at issue in this petition are based on proven 

expertise and in-service-verified design styles and practices. This experience and track 

record helps to ensure the reliability and safety ol the product. As explained further in the 

statements immediately below, the introduction of these engine models into service will 

generate valuable public benefits. 

• The granting of the requested exemption will expedite the entry into service of superior 

engines and engine technology that will enhance the safety and reliability of airline 

operations, and increase the efficiency of aircraft performance, thereby promoting U.S. 

economic interests (including those of U.S. airlines and their employees and shareholders} as 

well as those of the traveling public, while also reducing adverse effects on the environment. 

All of these enhancements constitute substantial public benefits. 

• Certification of the XWB engine by the U.S. will make additional aircraft models available for 

purchase by U.S. airlines. Such choices are in the economic interest of the U.S. through 

promotion of a more competitive market for large commercial transport aircraft. 

• These state-of-the-art engine models will reduce the operating costs of aircraft, and the 

airlines that operate them, relative to costs associated with aircraft that are currently in 

service. Such a reduction in operating costs will benefit U.S. and international airlines, their 

employees and shareholders. Moreover, such reduced operating costs provide the 

opportunity for airlines to offer more numerous, and less expensive, air service options to 

the traveling public. 

• The Trent XWB models will be installed on the Airbus A350, which has customers both 

within and outside the United States. 

• Certification of state-of-the-art engine models, when operated in the Airbus A350, will reduce 

fuel bum, thereby reducing harmful emissions such as carbon dioxide (CO·) and NO. from 

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levels experienced with engines currently in service. 

• The Trent XWB is built with U.S. supplied parts that constituting approximately 16% of the 

engine value. Sales of the engine contribute to the U.S. economy, support U.S. jobs, and 

enhance the U.S. balance of trade and gross domestic product, all of which promote the U.S. 

public interest. 

• Certification of the XWB engine in the U.S. promotes the regulatory standards of the U.S. as 

global bench mark for airworthiness. Promotion of the U.S. regulatory standards is in the public 

interest as this increases the number of goods and services available to U.S. citizens that are 

compliant with U.S. regulatory standards, and since many countries voluntarily adopt U.S. 

standards this process does not increase the burden on the U.S. government. 

E. Statement of No Adverse Effect on Safety 

The FAA's grant of this requested exemption will have no adverse effect on safety. Compliance with 

§ 33.27 is significant for safety purposes because it demonstrates that an engine's rotors will not fail 

under a varying range of potential operating conditions. The requirements contained in § 33.27(1} are 

significant for safety because this subsection allows failures of shaft sections to be excluded from the 

range of conditions considered under§ 33.27, but only if a design organization can demonstrate that 

the risk of such shaft section failures is sufficiently remote. Subsection 33.27(1)(6) does not in itself 

impose any additional safety requirement. Clearly, if risk of failure of the whole shaft system is 

considered and shown to be at least as remote as is acceptable for Nshaft sections,w then the overall 

level of safety must be at least equal to circumstances in which only Nshaft sections" are considered, 

as provided for under § 33.27(f}. Subsection 33.27(f)(6) was included in Section 33.27 based on a 

history of failures associated with conventional shalt systems, which raised doubt about the ability of 

design organizations to fully assess the potential failure modes (and failure rate) of an entire shaft 

system. However, for the HP shaft system of the Trent XWB (and indeed for other Rolls-Royce 

modern 3 shaft engines), this analysis can be carried out with high fidelity because: 

1. The HP shaft system design utilized across the Trent engine family differs significantly from 

conventional shaft systems. For example, it features no bearings or oil system components, 

has high stiffness and significant clearance relative to other shafts; consequently, the threats 

associated with the features of a conventional shaft do not apply. A Failure Mode and Effect 

Analysis has determined that there are no known or potential environmental threats to the 

integrity of the HP shaft system components that could lead to a loss of load failure. 

2. In order to ensure a high level of integrity, the special controls applied to the torquetransmitting components (i.e., the HP compressor rear drum and the HP turbine disc of the 

HP shaft system) are of a higher standard than those of many other shaft systems in the 

past. These mandated controls address, but are not limited to: 

• Material specifications; 

• Material properties (e.g., low cycle fatigue, high cycle fatigue, creep); 

• Manufacturing induced anomalies; 

• Service induced damage tolerance assessment; 

• Safe life mandatory inspections; and 

• Mandatory cycle life limitation. 

3. The theoretical assessment of points 1 ) and 2) above is supported by the service experience 

of the Rolls-Royce three shaft family of engines, all of which Incorporate the same design 

style for the HP shaft system as the Trent XWB engine models that are the subject of this 

petition. Over the course of more than 250 million service flight hours, there have been no 

failures of the HP shaft system torque path on the Trent family of engines. This performance 

reflects an extremely remote potential failure rate of less than 2.8 x 10-9 failures per flight 

hour. 

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In addition, in its Partial Grant of Exemption, Exemplion No. 10964, issued March 28, 2014 in 

Regulatory Docket No. FAA-2013-1049, the FAA concluded that granting Rolls-Royce's recent petition 

requesting an identical exemption for other Rolls-Royce Trent engine family models had no adverse 

effect on safety and was in the public interest, subject to the condition that the HP turbine disc burst 

speed is greater than 100% rotor terminal speed due to HP shaft system failure. 

In sum, there is ample evidence that analysis of the complete HP shaft system on the Trent XWB 

models at issue achieves the level of fidelity required for failures of shaft sections under§ 33.27(f). 

Therefore, the level of safety under the requested exemption will be at least equal to that otherwise 

provided by§ 33.27, thereby assuring that no adverse effect on safety will result from a grant of the 

requested exemption. 

F. Summary for Federal Register 

As set forth in section I below, Rolls-Royce is requesting that this petition be processed without 

publication in the Federal Register. If, however, the FAA determines that publication in the Federal 

Register is warranted, in accordance with § 11.81 (f), Rolls-Royce offers the following summary 

suitable for publication in the Federal Register. 

Petitioner. Rolls-Royce pic 

Section of 14 C.F.R. Artected: 14 C.F.R. § 33.27(f)(6) 

Description of Relief Sought: 

Rolls-Royce requests an exemption from 14 C.F.R. § 33.27(f)(6) to be applied to Rolls-Royce 

Trent XWB engine, models XWB-84, XWB-798, XWB-79 and XWB-75. Rolls-Royce seeks to 

exclude the entire HP shaft system from consideration In determining the highest overspeed 

that would result from a complete loss of load on a turbine rotor. 

G. Additional Supporting Information 

EASA Certification requirements CS-E 840 and CS-E 850 are similar requirements to those of§ 

33.27. The Trent XWB engine models at issue have been certified by EASA under Type Certificate 

E.111, which was released on 7 February 2013. To meet the requirements of CS-E 840 and CS-E 

850, EASA granted an Equivalent Safety Finding. The evidence provided to support this Equivalent 

Safety Finding was similar to that provided in this petition for exemption. The Equivalent Safety 

Finding was accepted by EASA on 15 January 2013. 

H. Privileges of this Exemption Outside the United States 

Pursuant to 14 C.F.R. § 11.81(h), Rolls-Royce requests that the privileges of this exemption be 

extended outside the United States. This extension of privileges Is necessary for operations based 

within foreign countries having bilateral agreements with the United States accepting FAA 14 C.F.R. 

Part 33 as their airworthiness standards for transport category aircraft. The Trent XWB is intended 

for the global marketplace, with customers based in countries utilizing the U.S. airworthiness 

standards. 

I. Good Cause Exists to Issue the Exemption without Notice and Comment 

Pursuant to 14 C.F.R. § 11.87, Rolls-Royce requests that this petition be processed without 

publication in the Federal Register for notice and comment, as may otherwise be required. RollsRoyce believes that good cause exists to not delay this action because: a) granting of this petition will 

not set a precedent since the petition seeks the same exemption granted by the FAA on March 28, 2014 

in Exemption No. 10964, Regulatory Docket No. FAA-2013-1049; b) the relief requested is ertectively 

identical to that granted in Exemption No. 10964 and in the Equivalent Safety Finding previously 

accepted by EASA; (c) delaying the action would adversely affect Rolls-Royce because the Trent 

XWB engine models covered by this petition are currently undergoing cross-validation with the FAA 

expected to complete in September 2014; and (d) this petition is timely filed. 

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~::(fsz;;:;tyr Tunde Oyinloye 

Airworthiness Engineer 

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Date: Wednesday 13th August, 2014 

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