] of 4 

GE Aviation 

-X^-H 

•I -' .^i General Electric Company, BBC15 

P. O. Box 156301, One Neumann Way 

, -, . ,. ^ _ Cincinnati, OH 45215-6301 

' i:- J , 513 243-9478 

513 243-9478 FAX 

Email Paul.Hill1igge.com 

bcc: File/LB 

GEnx/PAH/034/11 

July 25, 2011 

U.S. Department of Transportation, 

DocKet Management System, 

400 7*^ Street, SW., Room PL 401, 

Washington. DC 20591-0001 

GO: 

Federal Aviation Administration 

New England Region 

12 New England Executive Park 

Burlington, MA 01803 

Subject: Petition for Exemption to FAR 33.83(d) for GEnx-2B (all models) Aircraft Engines 

Gentlemen: 

In July 2010 General Electric was granted an amended type certificate which included the GEnxGEnx-1B54. GEnx-1B57, GEnx-1B64, GEnx-1B67, GEnx-1B70 and GEnx-2B67 turbofan 

engines. In October 2010 GE made application for several GEnx-2B67 derivative models. 

These models are yet to be certified derivatives of the currently certified GEnx-2B67 which is 

listed on type certificate E00078NE. 

With the pursuit of increased fuel efficiency and subsequent technology enhancements of 

modern commercial aircraft some older sections of the FAR are not in line with modern aircraft 

and turbine engine design philosophies. One of these sections is 33.83(d) [vibration survey] 

which was introduced in the 1960's. Airframer designed engine inlets are designed to optimize 

aircraft aerodynamic and acoustical efficiencies thus enhancing aircraft fuel efficiency. In some 

cases the engine inlets are designed such that airflow into the inlet separates above certain 

cros$wind levels thus causing increased engine fan blade and engine fan outlet guide vane 

(OGV) vibratory stress. This is the case for the Boeing 747-8 (all models) and the GEnx-2B (all 

models). At crosswinds above 25 knots and at low relative aircraft forward velocities (take-off 

roll) the airframer designed inlet can have separated air flow thus causing a transient violation of 

33.83 (d) for the engine fan blades and engine fan outlet guide vanes (OGV's). 

Background: 

For the GEnx-2B (all models)/Boeing 747-8 (all models) applications the airframer has requested 

the ability to take-off at crosswinds up to 45 knots. 
2 of 4 

GE is requesting an exemption to CFR 14 Part 33 Section 33.83 (d) for the GEnx-2B (all 

models). Section 33.83(d) states: 

"(d) Except as provided by paragraph (e) of this section, the vibration stresses associated with 

the vibration characteristics determined under this section, when combined with the appropriate 

steady stresses, must be less that the endurance limits of the materials concerned, after making 

due allowances for operating conditions for the permitted variations in properties of the 

materials. The suitability of these stress margins must be justified for each part evaluated. If it 

is determined that certain operating conditions, or ranges, need to be limited, operating and 

instailation limitations shall be established." 

Specifics of the Exemption Request: 

GE requests that the GEnx-2B (all models) fan blades and fan OGV's be exempted from the 

requirements in bold below. 

'(d) Except as provided by paragraph (e) of this section, the vibration stresses associated 

with the vibration characteristics determined under this section, when combined with the 

appropriate steady stresses, must be less that the endurance limits of the materials 

concerned, after making due allowances for operating conditions for the permitted 

variations in properties of the materials." 

It has been determined that an equivalent level of safety to the requirements of 33.83 (d) still 

exists for the GEnx-2B (all models) fan blades and fan OGV's. 

Reason for Request: 

This exemption is being requested to accommodate a transient engine inlet, fan blade, and OGV 

vibratory interaction at crosswinds above 25 knots. The General Electric Company has 

determined via analysis that, even though material endurance limits are exceeded transiently 

during take-off, the levels of stress encountered on the fan blade and OGVs result in Low Cycle 

Fatigue (LCF) cyclic lives well in excess of the required minimum LCF cyclic lives needed to 

preclude an airworthiness limitation on those parts. 

Granting of this exemption is in the public interest because it will: 

(1) Not adversely affect flight safety since a level of safety equivalent to that ensured by 14 

CFR Part 33 Amendment 21, Section 33.83 (d) has been determined. 

(2) Allow for the continued use and grovrth of high by-pass turbofan engines. High Bypass 

ratio turbofan engines are fuel efficient and extremely economical to operate for the worlds 

airlines and allow for long range engine operation as in the Boeing 787 and 747-8 aircraft. 

Increasingly longer routes with increasingly larger aircraft and payloads are requiring 

increases of engine thrust levels. With improved aerodynamic, more fuel efficient and 

noise reducing aircraft designs it has become difficult to stay within material endurance 

limits at crosswinds above 25 knots and low relative aircraft velocities. 
3 of 4 

(3) Maintain a positive effect on the US economy. There is a potential for adverse impact to 

engine/airplane sales. Note that the GEnx-2B67 engine is the sole engine for the B747-8 

Growth airplane, as such there is no domestic competition engine. The competition for 

the 747-8/GEnx-2B67 market is solely outside of the United States. Thus the loss of a 

campaign will be to a non-US business. A Boeing 747, including the engines has a value 

of $150-180 million; a typical sale would include 6-10 aircraft. With a product as large as 

the Boeing 747 and the GEnx-2B67 engines, any sale of the product has a clear positive 

impact to the U.S. public. The additional sales of the product will be in the public interest 

as the sale has the impact of retaining current employment, with the potential of increasing 

employment. In addition, increasing the number of airplane engine sales to foreign 

countries will have a positive impact to the US economy and balance of trade. 

(4) Decrease administrative burden to the FAA and to GE. 

The intent of 33.83(d) is to show that the engine hardware will not fail due to vibration 

induced stresses. The critical item is the capability of the aircraft to meet the required 

performance characteristics while, at the same time, ensuring that the engine hardware 

does not fail. Airframer designed engine inlets for high bypass ratio turbo fan engine and 

large airplane applications are designed to optimize aircraft aerodynamic and acoustic 

efficiencies thus enhancing overall aircraft fuel efficiency and, typically, engine 

manufacturers do not have an input into the inlet design. Separated flow engine fan blade 

and fan OGV vibration often occurs at high cross wind levels and low relative aircraft 

velocities. A ruling in favor of this request for exemption would eliminate the need for GE 

to pursue an ELOS and for the FAA to write issue papers for future GEnx-2B67 engine 

derivatives thus decreasing administrative burden to the FAA and to GE. 

Based on the above justification, full compliance with the "in service" aircraft requirements, and 

public interest General Electric requests exemption from the "must be less that the endurance 

limits of the materials concerned" requirement within FAR 33.83 (d) for the GEnx-2B67 engine 

models (all models). 

Summary (for Publish in Federal Reqister) per FAR Part 11 Section 11.81(f) 

Petition for Exemption 

In July 2010 General Electric was granted an amended type certificate which included the GEnx1B and 28 turbofan engine models. In October 2010 GE made application for GEnx-2B 

derivative models. These models are yet to be certified derivatives of the currently certified 

GEnx-2B67 which is listed on type certificate E00078NE. 

With the pursuit of increased fuel efficiency and subsequent technology enhancements of 

modern commercial aircraft some older sections of the FAR are not in line with modern aircraft 

design philosophy. One of these sections is 33.83 (d) [vibration survey] which was introduced in 

the 1960's. Airframer designed engine inlets are designed to optimize aircraft aerodynamic and 

acoustical efficiencies thus enhancing aircraft fuel efficiency. In some cases the engine inlets are 

designed such that airflow into the inlet separates, thus causing increased engine fan blade and 

engine fan outlet guide vane (OGV) vibration. This is the case for the 747-8 (all models) and the 

GEnx-2B (all models). At crosswinds above 25 knots the airframer designed inlet can have 
4 of 4 

separated air flow thus causing a transient violation of 33.83 (d) for the engine fan blades and 

engine fan OGV's. 

General Electric requests exemption from the "must be less that the endurance limits of the 

materials concerned" requirement within FAR 33.83 (d) for the GEnx-2B (all models) engine 

models fan blades and fan OGV's. 

14CFR Part 33 Amendment 21 Section 33.83 (d)) states: 

Except as provided by paragraph (e) of this section, the vibration stresses associated with the 

vibration characteristics determined under this section, when combined with the appropriate 

steady stresses, must be less that the endurance limits of the materials concerned, after 

making due allowances for operating conditions for the permitted variations in properties of the 

materials. 

General Electric is requesting an exemption to the "must be less that the endurance limits of 

the materials concerned" requirement since it has been determined that an equivalent level of 

safety exists. 

End Summary 

Sincerely, 

fl^ l ^ ^ 

Paul A. Hill 

FAA-DER 

Principal Engineer, Airworthiness&Certification