Enclosure to RA-15-01262

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Petition for Extension of Limitation from Exemption No. 11070A

The Boeing Company

Douglas M. Lane, Director, Regulatory Administration.

The Boeing Company

PO Box 3707

Seattle, Washington, 98124

Section of the Code of Federal Regulations (CFRs) that are affected

Regulation At

Amendment

Which Requires

§25.939(a) 25-40 (a) Turbine engine operating characteristics must be 

investigated in flight to determine that no adverse 

characteristics (such as stall, surge, or flameout) are 

present, to a hazardous degree, during normal and 

emergency operation within the range of operating 

limitations of the airplane and of the engine.
Enclosure to RA-15-01262

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The Original Extent of Relief Sought and Reason(s):

Regulation Requires: Relief is necessary because:

§25.939(a) 

Amendment 

25-40

747-8/-8F airplanes

powered by GEnx-2B

engines incorporating

Electronic Engine 

Control (EEC) C068

software (and later 

EEC software

versions), and

operating within the

associated GEnx-2B 

Ice Crystal Icing (ICI) 

engine limitation

envelope certified 

under ODA Project 

Number PS14-0053, 

are required to comply 

with turbine engine 

operating 

characteristics 

requirements of 

§25.939(a).

The GEnx-2B engines installed on 747-8/-8F 

airplanes have experienced engine flameout and 

engine mechanical damage in Ice Crystal Icing 

(ICI) conditions in-service. The engine reaction 

in ICI conditions resulted in the issuance of AD 

2013-24-01, to address the unsafe condition. 

ODA Project Number PS14-0053, will certify a 

revised AFM Certificate Limitation and Operating 

Procedure to account for the GEnx-2B engine 

limitation associated with GEnx-2B Electronic 

Engine Control (EEC) software version C068. 

The ICI functionality in C068 was developed 

through the use of computational fluid dynamics 

(CFD) modeling validated by engine testing at 

the GE Winnipeg Test, Research and 

Development Centre. The EEC software reduces 

the risk of flameout/rollback to a remote 

possibility, but is insufficient to fully mitigate the 

mechanical damage events, through the full 

airplane operating envelope.

The revised AFM Certificate Limitation and 

Operating Procedure were developed to prohibit 

airplane operation at engine power levels that 

could result in ice crystal accretion leading to 

mechanical damage. The AFM revision 

associated with this interim solution raises the 

current ICI operating floor from 30,000 feet to 

35,500 feet with use of a flight crew procedure to 

maintain adequate engine power levels, 

implemented via minimum Mach number and 

gross weight operating limitations.

The FAA recently clarified that in-flight power 

setting restrictions under a crew procedure to 

avoid conditions that would result in 

unacceptable operating characteristics does not 

meet the intent of §25.939(a).

With this petition for exemption, Boeing is 

requesting relief for a limited period to allow 

sufficient time to develop, validate, and certify an 

engine configuration that is fully compliant with 

§25.939(a).
Enclosure to RA-15-01262

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The requested time-limited partial exemption will

provide relief from the turbine engine operating

characteristics requirements of §25.939(a) for 

new production and in-service Boeing Models 

747-8F and 747-8 incorporating EEC C068 

software (or later EEC software versions), and 

upon modification of the AFM to reflect the 

applicable GEnx-2B / C068 (and later EEC 

software versions) engine ICI limitation. The 

relief sought is limited to 747-8/-8F airplanes 

prior to the incorporation of an engine 

configuration compliant to §25.939(a). 

Certification of a compliant design will be 

accomplished by 31 December 2015, or the 

operation of the airplanes would revert to the

existing AFM Certificate Limitation and 

Operating Procedure certified under ODA 

Project Numbers PS12-0298 and PS13-0956.

Certification of the Interim ICI Limitation has 

been more complex than initially estimated. In 

parallel, Boeing and GE have been working the

development of software supporting the final

compliant configuration, which has also taken

more time than anticipated. Evaluation and

incorporation of the results of the extensive 

NASA Glenn Testing are anticipated to take 

several months.

Review of data with regulatory agencies and

finalization of an agreed to cert approach will

follow. Based on the previously mentioned items,

the estimated completion date of a design

compliant to §25.939(a) is December 31, 2015.

This requested time-limited partial exemption will

apply to future design changes requiring

assessment of §25.939(a) while the AFM

Certificate Limitation and Operating Procedure 

are necessary for safe operation in ICI 

conditions.
Enclosure to RA-15-01262

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Description of Issue

The GEnx-2B engines installed on 747-8/-8F airplanes have been shown to be susceptible to 

flameout / engine damage during operation in ICI conditions. Ingestion of ice crystals results 

in accretion in the propulsor at the booster outlet guide vanes (BOGV), fan hub frame (FHF) 

outer flow path, and the HPC inlet guide vanes (IGV). ICI logic included in GEnx-2B EEC 

software version C068 (and later EEC software versions) reduces the risk of flameout/rollback 

to a remote possibility within the envelope associated with the ICI engine limitation. EEC C068 

software certified under ODA Project Number PS14-0545, detects the presence of ice crystal 

icing and activates the cycling of the variable bleed valve (VBV) doors. The AFM revision 

associated with this interim solution (ODA Project Number PS14-0053) raises the current ICI 

operating floor from 30,000 feet to 35,500 feet with use of a flight crew procedure to maintain 

adequate engine power levels, implemented via minimum Mach number and gross weight 

operating limitations. This ICI logic in conjunction with the revised AFM limitation for 

avoidance of ICI conditions will be substantiated as effective in identifying ICI conditions and 

addressing the ICI threat, when operating in ICI conditions in-service. The FAA recently 

clarified that in-flight power setting restrictions under a crew procedure to avoid conditions that 

would result in unacceptable operating characteristics does not meet the intent of §25.939(a). 

Therefore, Boeing is requesting this time-limited exemption in order to implement an engine 

configuration compliant to §25.939(a) prior to the expiration of this time-limited exemption.

The above text was associated with the Boeing request of January 2015 for revision of TLE 

11070. In that request, as is identified above in The Original Extent of Relief Sought and 

Reason(s):, Boeing requested an exemption end date of December 31, 2015. The FAA, in 

their grant of TLE 11070A, dated February 2, 2015 (Regulator Docket No. FAA-2014-0299), 

approved an exemption end date applicable for 14 CFR 25.939(a) of June 30, 2015. The FAA 

rationale in selecting the June 30, 2015 date is “Extending the deadline for the final design 

modifications would require more data and a thorough FAA review and would not support the 

timeline of Boeing's request for granting the amended exemption”. The material following 

provides more detailed rationale, which is based on the program timeline associated with the 

recent interim limitation revision effort. The timeline of this recent effort clearly identifies a 

more appropriate end date for TLE 11070A as applies to 14 CFR 25.939(a) would be the 

December 31, 2015. Data collection at NASA Glenn has just very recently been concluded. 

Processing of this data and Boeing/GE ICI team engagements will continue well into 2015. 

Following this, there will be significant Boeing/FAA engagement and FAA review time 

associated with the certification of a configuration no longer requiring an exemption to the

requirements of 14 CFR 25.939(a). Finally, the impact of the end date associated with this 

TLE was clearly identified by the FAA in the issue of TLE 11070A - Boeing must show full 

compliance to 14 CFR 25.939(a), at Amendment 25-40, for newly produced Model 747-8 and 

747-8F airplanes in order to receive a certificate of airworthiness after June 30, 2015.
Enclosure to RA-15-01262

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Relief from the original schedule is necessary because:

The current RA Project (PS14-0053) associated with revising the AFM Certificate Limitations 

and Operating Procedures has taken 11 months from the initial testing at Winnipeg to the 

release of 14 CFR Part 25 approved documents. The key activities in this timeframe were:

1) The analysis of significant amounts of data from Winnipeg in conjunction with significant 

amounts of GEnx and Legacy data,

2) The model prediction of the benefit of the ICI logic to our flameout engine reaction

3) The discovery of root cause for our mechanical damage, both in location and accretion 

characteristic, and

4) The translation of the revised engine limitation into acceptable Part 25 procedures. 

Acknowledged during this interim AFM limitation project was the fact that substantiating an 

engine configuration that eliminated the need for an Ice Crystal Icing (ICI) operational 

limitation would involve simulated altitude testing. That testing began at the end of November 

2014 and has been acquiring data into March, 2015. The effort associated with analyzing the 

significant volume of test data, further validating the CFD model, confirming a completely 

operable and compliant engine configuration, and preparing the necessary substantiating data 

to achieve both 14 CFR Part 33 and Part 25 compliance is expected to require an equivalent 

time that the interim AFM limitation exercise involved.

Boeing’s goal is to certify an engine configuration capable of full ICI limitation removal as 

quickly as possible. Recent experience of realistic progress for all the necessary pieces 

supporting certification strongly influences a requested TLE end date of Dec 31, 2015.

Statement of No Adverse Affect on Safety Due to Schedule Extension

As was stated in Boeing petition letter RA-15-00349, the proposed AFM Certificate Limitation 

and Operating Procedure for operating near or in ICI conditions require the flight crew to 

maintain a minimum Mach, which maintains an adequate level of safety for the time period of 

this Exemption. The use of this AFM Certificate Limitation is consistent with other AFM 

Certificate Limitations such as Engine Anti Ice System, Weight Limitations and Center of 

Gravity Limits, and Ground Operations in Icing Conditions. Boeing has determined that this 

AFM limitation is acceptable from a workload and complexity standpoint, and is operationally 

feasible. Boeing contends that a 6 month increase in the time period of this exemption will not 

compromise the level of safety for the airplane associated with the AFM Certificate Limitation 

and Operating Procedure for operating near or in ICI conditions. 

Statement of Public Interest

As the FAA determined in issuing Exemption No 11070, and reiterated in issuing Exemption 

No. 11070A – “The FAA has determined that the justification for the issuance of Exemption 

No. 11070 remains valid with respect to this amendment and is in the public interest.”, Boeing 

asserts that the public interest rationale is still applicable to this requested extension.
Enclosure to RA-15-01262

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Request to Waive Publication and Comment

Boeing requests that this revision to Time-Limited Exemption 11070A be waived as this is 

considered a minor addition to the existing exemption. Boeing contends the rationale stated 

by the FAA, associated with granting TLE 11070A - Full compliance must be demonstrated 

prior to removal of all associated limitations. Therefore, the FAA has determined that good 

cause exists for not publishing a summary of the petition, for public comment, in the Federal 

Register because the requested amendment to the exemption would not set a precedent, and 

any delay in acting on this petition would be detrimental to The Boeing Company and 

operators and flight crews of747-8/-8F airplanes. – is quite applicable to this requested 

revision of end date.

Privileges of this Exemption Outside the United States

Per §11.81(h), Boeing 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 CFR Part 25 

as their airworthiness standards for transport category aircraft. The 747-8F and 747-8 are 

intended for the global market place with a launch customer based in a country utilizing the 

United States airworthiness standards.

Conclusion

Boeing requests an additional six (6) month extension to allow sufficient time for Boeing to 

complete the test, analysis and compilation of substantiating documentation required to certify 

a configuration fully compliant with the requirements of 14 CFR Part 25.939(a). This would 

result in an Exemption termination date of 31 December 2015 for airplanes that have not been 

issued an original airworthiness certificate prior to this date. 

Summary to be Published in the Federal Register

PETITIONER: Boeing Commercial Airplanes

SECTION OF 14 CFR AFFECTED: §25.939(a)

DESCRIPTION OF RELIEF SOUGHT: The Boeing Company has requested additional 

compliance time until 31 December 2015 (an additional 6 months) for airplanes that have 

not been issued an original airworthiness certificate prior to this date, to define and 

certify a configuration fully compliant with §25.939(a) for GEnx-2B powered 747-8/8F 

airplanes.