ANE

- 1 5

- 574

- E Exemption No. 11686

UNITED STATES OF AMERICA DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION BURLINGTON, MA 01803

- 5229

In the matter of the petition of

ROLLS

- ROYCE plc Regulatory Docket No. FAA

- 2015

- 0156 for an exemption from § 33.27(f)(6) of Title 14, Code of Federal Regulations

PARTIAL GRANT OF EXEMPTION

On January 23, 2015

, Ms. Rebecca Peacock, Airworthiness Specialist, Rolls

- Royce plc , ML

- 52, PO Box 31, Derby, DE24 8BJ, England, petitioned the Federal Aviation Administration (FAA) on behalf of Rolls

- Royce, plc for an exemption from § 33.27(f)(6), Amendment 33

- 31 of Title 14, Code of Federal Regulations (14 CFR). The proposed exemption , if granted, would allow some high

- pressure (HP) shafts to be exempted from 14 CFR § 33.27(f)(6).

The petitioner requests relief from the following regulation:
Section 33.27(f)(6), Amendment 33

- 31 prescribes that:

“(f) Failure of a shaft section may be exc luded 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.”

The petitioner supports its request with the following information:

Th e p etitioner requests the FAA grant the exemption based on two points. The p etitioner’s f irst point is that t he design of the HP shaft system in each of the Trent 1000 engine models it identifies, is not amenable to analysis by shaft section. The p etitioner’s s econd point is that they are not able to show compliance with § 33.27 without an exemption from § 33.27(f)(6). H owever, t he petitioner claims to be able to show compliance , with at least an equal level of safety to that required to meet § 33. 27, if we grant the exemption

.

The p etitioner requests exemption from 14 C.F.R. § 33.27(f)(6) for the HP shaf t system of the following new Trent 1000 engine models:2

Model Rating x 1000 lbs.

Trent 1000

- AE 6 4 Trent 1000

- CE 7 0 Trent 1000

- AE2 64 Trent 1000

- CE2 70

The p etitioner asserts that

, as demonstrated in its substantiating report, the level of safety afforded by compliance with § 33.27 for the HP shaft system will be unaffected by granting an exemption from § 33.27(f)(6). The p etitioner also states that granting this exemption will promote and serve the public interest, and petitioner identified those benefits in its package.

Finally, petitioner asserts that granting its petition will have no adverse effect on safety . The petitioner prov ided the following in support of that contention.

1. The HP shaft system design us ed across the Trent engine family differs significantly from conventional shaft systems. 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 failure from a loss of load.

2. T he special controls applied to the torque transmitting components (i.e., the HP Compressor Rear Drum and the HP Turbine disc of the HP shaft system) are of a higher
standard to ensure a higher level of integrity than those of many other shaft systems in the past.

3. The service experience of the Rolls

- Royce three

- shaft family of engines, all of which incorporate the similar design style for the HP shaft system as the Trent 1 000 engine models that are the subject of this petition, support the theoretical assessme nt of points 1) and 2) above. Over the course of more than 256 million service flight hours, no HP shaft system torque paths hav e failed on the Trent family of engines. This performance reflects an extremely remote potential failure rate of less than 2.7 x 10

- 9 failures per flight hour.

Federal Register P ublication

T he FAA determine d that publishing the petitioner’s request for exemption in the Federal Register for public comment was necessary , per 14 CFR 11.87

. We published a summary of the petition in the Federal Register on March 31, 2015 (80 FR 17138 ) , for a 10 day period

. We

re ceived one commen t acknowledging the exemption which reference d an FAA request to form a separate advisory group for review of overspeed standards

. The complete petition is available at the Department of Transportation’s Federal Docket Management System at http://regulati ons.gov under Docket No. FAA

- 2015

- 0156

.3

The FAA’s a nalysis is as follows:

We reviewed the data provided by the petitioner

, and find all known failure modes were identified and consider ed that can lead to an overspeed condition . The compensating factors that the petitioner demonstrated through good service experience of similar three

- shaft design systems a re acceptable except one. T he histo rical data (good experience) regarding the low

cycle fatigue ( LCF ) failure mechanism is not applicable to this desig n . The life

- limited location for some of the Trent 1000 engine models is on the torque path

, which is different than the petitioner’s experience. The LCF lives for the las t stage of the HPC and HPT disk s for the Trent 1000 engines models are much lower than the previous experience

. The new Trent 1000 engines models are operati ng at higher stress conditions and bu rst margins are lower than previous experience.

Based on our finding

, an additional compensating factor is needed to show an equiva lent level of safety. Therefore as a compensating factor any feature on the HP shaft system that has a predicted safe cyclic life less than 150 percent of the declared safe cyclic life (DSCL) limit must be eddy current inspected within 15 0 cycles of two

- t hirds of the DSCL limit of the part. Based
on t he compensating factors that the petitioner demonstrated through good service experience of similar three

- shaft design systems , the additional compensating factor listed above

, and evaluation of all known fai lure modes, we conclud e that an exemption to § 33.27(f)(6 ) for the Trent 1000

- AE

, Trent 1000

- CE

, Trent 1000

- AE2 , and Trent 1000

- CE2 engine models will have no adverse effect on safety.

The FAA’s Decision

In consideration of the foregoing

, I find that a partial grant of exemption is in the public interest. Therefore, pursuant to the authority contained in 49 U.S.C. §§ 106(f), 40113 and 44701, delegated to me by the Administrator, Rolls

- Royce plc , is granted a n exemption from 14 CFR § 33.27 ( f )( 6 ) , subject to the conditions and limitations listed below.

Conditions and Limitations

1. A ny feature on the HP shaft system that has a p redicted s afe c yclic l ife less than 150 percent of the DSCL limit must be eddy

- c urrent inspected within 15 0 cycles of two

- thirds of the DSC L limit of the part

. Issued in Burlington, Massachusetts, on May 22, 2015.

/s/

Thomas A. Boudreau A cting Manager, Engine and Propeller Directorate Aircraft Certification Service