DE24 8BJ England 

Tel: (+44) 1332 249905 

richard.shepherd@ rolls-royce.com 

B. Pertinent Section of the Code of Federal Regulations 

Rolls-Royce hereby petitions for an exemption from 14 C.F.R. § 33.27(f)(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 determining the highest 

overspeed that would result from a complete loss of load on a turbine rotor if the 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 of the 

following Trent XWB engines models: 

Model 

Trent XW B-84 Trent XW B-798 Trent XWB-79 Trent XWB-75 

Rating x 1000 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 granting of the exemption from§ 33.27(f)(6) 

requested herein. 

Relief from§ 33.27(f)(6) is sought because analysis has failed to show that failure of the HP 

shaft system can never result in overspeed to burst. The design of the HP shaft system is not 

amenable to analysis by shaft section. Rolls-Royce therefore 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. However, as 

demonstrated in Section E below, 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(1)(6). 

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, with at 

least an equal level of safety to that required to meet§ 33.27, if the exemption is granted. 

Rolls·Royce pic Registered offlce:65 Buckingham Gate, London SW1 E 6AT 

Company number: 1003142. Registered In England. 

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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 over 41 years and more than 265 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 of the product. As explained further in the points 

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

valuable public benefits. 

b. 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 travelling public, while also reducing adverse effects on the 

environment relative to older engine types on other aircraft. All of these enhancements 

constitute substantial public benefits 

c. 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 and less expensive air service options to the traveling 

public. 

d. These state-of-the-art engine models, including the proposed modifications, when operated 

in the Airbus A350, will reduce fuel burn, thereby reducing harmful emissions such as 

carbon dioxide (C02) and NOx from levels experienced with other older engine types 

currently in service on other aircraft. 

e. These state-of-the-art engine models, including the proposed modifications 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. 

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

within and outside the United States. 

g. The Trent XWB is built with U.S. supplied parts that constitute 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 

Rolls-Royce pic Registered office:65 Buckingham Gate, London SW1 E 6AT 

Company number: 1003142. Registered In England. 

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in § 33.27(f) 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(f)(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 "shaft sections," then the overall level of safety must be at least equal to 

circumstances in which only "shaft 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 shaft 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: 

a. 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. 

b. 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: 

1. Material specifications; 

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

3. Manufacturing induced anomalies; 

4. Service induced damage tolerance assessment; 

5. Safe life mandatory inspections; and 

6. Mandatory cycle life limitation. 

c. 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 265 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 2.6 x 10-9 

failures per flight hour. 

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. · 

Rolls-Royce pic Registered office:65 Buckingham Gate, London SW1E SAT 

Company number: 1003142. Registered in England. 

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

F. Additional Supporting Information 

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

33.27. The existing Trent XWB engine models have been previously certified by EASA under 

Type Certificate E.111. 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 January 15th, 2013. 

G. Privileges of this Exemption Outside the United States 

Per 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. 

H. Good Cause exists to issue the Exemption without Notice or 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. 

Rolls- Royce believes that good cause exists to not delay this action because: 

a. the relief requested is effectively identical to an Equivalent Safety Finding previously 

accepted by EASA 

b. delaying the action would adversely affect Rolls-Royce because the Trent XWB engine 

models covered by this petition are currently in service operation and future modification 

of the design will be required to address service issues and maintain reliability and 

maintain the competitiveness of the product.; and 

c. this petition is timely filed. 

Respectfully submitted, 

Richard Shepherd 

Airworthiness Specialist 

Rolls-Royce pic 

Date; 23m December 2015 

Rolls-Royce pic Registered office:65 Buckingham Gate, London SW1E SAT 

Company number: 1003142. Registered In England. 

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