Petition for Extension of Limitation from Exemption No. 11081A

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 A 

RA-15-01286 

Page 1 of 6
The Original Extent of Relief Sought and Reason(s):

Regulation Requires: Relief is necessary because:

§25.939(a) 

Amendment 

25-40 

787-8/-9 airplanes 

powered by GEnx-1B

engines incorporating

Electronic Engine 

Control (EEC) B178 

software (and later 

EEC software 

versions), and 

operating within the 

associated GEnx-1B 

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-1B engines installed on 787-8/-9 

airplanes have experienced engine flameout in 

Ice Crystal Icing (ICI) conditions in-service. 

The GEnx-2B engine, powering the 747-8/-8F 

airplane, has experienced mechanical damage 

in ICI conditions. This engine’s damage 

resulted in the issuance of AD 2013-24-01, 

which is applicable to both the GEnx-1B and 

GEnx-2B engine configurations, to address the 

unsafe condition. ODA Project Number PS14-

0053, certified a revised AFM Certificate 

Limitation and Operating Procedure to account 

for the GEnx-1B engine limitation associated 

with GEnx-1B Electronic Engine Control (EEC) 

software version B178. The ICI functionality in 

B178 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 37,500 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 

Enclosure A 

RA-15-01286 

Page 2 of 6
an engine configuration that is fully compliant 

with §25.939(a). 

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 787-8 and 787-9 incorporating 

EEC B178 software (or later EEC software 

versions), and upon modification of the AFM to 

reflect the applicable GEnx-1B / B178 (and 

later EEC software versions) engine ICI 

limitation. The relief sought is limited to 787-8/-

9 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 A 

RA-15-01286 

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Description of Issue 

The GEnx-1B engines installed on 787-8/-9 airplanes have been shown to be susceptible to 

flameout 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-1B EEC software version B178 

(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 B178 software, certified 

under ODA Project Number PS14-0621, 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 37,500 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 11081A, dated January 30, 2015 (Regulator Docket No. FAA-2014-0330), 

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 11081A 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 11081A - Boeing must show full 

compliance to 14 CFR 25.939(a), at Amendment 25-40, for newly produced Model 787-8 and 

787-9 airplanes in order to receive a certificate of airworthiness after June 30, 2015.

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 

Enclosure A 

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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-15-00350, 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 11081, and reiterated in issuing Exemption 

No. 11081A – “The FAA has determined that the justification for the issuance of Exemption 

No. 11081 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 A 

RA-15-01286 

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Request to Waive Publication and Comment

Boeing requests that this revision to Time-Limited Exemption 11081A 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 11081A - 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 of 787-8/-9 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 787-8 and 787-9 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-1B powered 787-8/-9 

airplanes. 

Enclosure A 

RA-15-01286 

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