U.S. Department 

of Transportation 

Federal Aviation 

Administration 

December 23, 2015 

Mr. Douglas M. Lane 

Director, Regulatory Administration 

The Boeing Company 

P.O. Box 3707, MC 03-56 

Seattle, W A 98124-2207 

Dear Mr. Lane: 

Transport Airplane Directorate 

1601 Lind Avenue, S.W. 

Renton, Washington 98057-3356 

Exemption No. 11 070C 

Regulatory Docket No. FAA-2014-0299 

This letter is to inform you that we have granted your petition for another amendment to 

Exemption No. 11070. It explains the basis for our decision and describes its effect. 

The Basis for Our Decision 

By letter no. RA-15-03488, dated August 28,2015, you petitioned the Federal Aviation 

Administration (FAA), on behalf of The Boeing Company, for another amendment to 

Exemption No. 11070. A previously granted amendment to the exemption (Exemption 

No. 11 070A) allows substituting laboratory and ground tests for the requirement to 

investigate engine operating characteristics in flight. It also permits use of airplane speed as 

a means to set minimum engine power needed to maintain engine operability in ice crystal 

icing (ICI) environments. Since granting the original exemption, the FAA has concurred 

with Boeing's proposal to utilize data gathered from in-service events in combination with 

ground tests and analysis as a means of compliance with the requirement of§ 25.939(a) to 

investigate engine operating characteristics in flight. However, the Boeing-proposed 

airplane flight manual (AFM) limitations and operating procedure for operating near or in 

ICI conditions, requiring the flightcrew to maintain a minimum airplane speed, is not 

directly compliant with§ 25.939(a). Therefore, the amendment requested by Boeing would 

extend the time-limited grant of exemption to September 30, 2016, and allow certification of 

a configuration that removes the operational limitations imposed by the airworthiness 

directive (AD) action. The time extension is necessary to allow Boeing sufficient time to 

validate and certify an engine configuration that is fully compliant with§ 25.939(a), 

Amendment 25-40, of Title 14, Code ofFederal Regulations (14 CFR). 

In the petition submitted to support Exemption No. 11 070B (extending the time-limited 

relief from § 25.939(a) to December 31, 2015), Boeing estimated that certification of a fully 

compliant engine configuration by the end of2015 would be achievable. However, Boeing 

states that the numerous certification projects associated with the final ICI limitation 
revision have taken more time than initially estimated. In addition, the evaluation of the 

results of the extensive testing conducted at the National Aeronautics and Space 

Administration (NASA) Glenn Research Center has also taken more time than anticipated. 

2 

We have reviewed the data provided by Boeing and have determined that the additional time 

requested will allow Boeing to complete the analysis and compilation of substantiating 

documentation required to demonstrate full compliance with the requirements of 

§ 25.939(a). 

For the reasons cited in the original petition and repeated in the request for amendment, the 

FAA agrees with Boeing's statement of public interest. Therefore, we find that extending 

the expiration for this time-limited exemption to September 30, 2016, is in the public 

interest. 

In addition, 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 flightcrews of747-8/-8F airplanes. 

In the petition for amendment, Boeing requested clarification on the following: 

Boeing requests that the FAA clarify whether it was the FAA intent, with the 

sentence "Design changes and modifications to in-service Model 747-8 and 747-8F 

airplanes involving engine ice-protection systems and associated [airplane flight 

manual] AFM limitations made after December 31,2015, must also fully comply 

with§ 25.939(a) at Amendment 25-40," to include revenue service airplanes in the 

exemption. 

This requirement has been included in all amendments to this exemption and was added 

when Boeing requested that the FAA add time-limited relief from§ 25.939(a) to Exemption 

No. 11070. The original intent of this provision was to require that design changes approved 

after December 31 , 2015, for existing airplanes (modifications) be compliant with 

§ 25.939(a). However, Boeing expressed concerns that this provision could force operators 

to complete major modifications to multiple engines at the same time. Since § 25.939(a) 

applies to the airplane, and not just to individual engines, this provision would require that 

all four engines be modified to bring them into compliance at the same time. This is a 

practice advised against in Boeing and industry publications because of possible 

maintenance errors that would be repeated on multiple engines, potentially introducing 

significant common-cause safety problems. We have considered Boeing's concerns and 

have removed the reference to modifications from the provision and extended the date to 

September 30, 2016. This will allow approval of service instructions that are not directly 

compliant until that time. The service instructions approved prior to that date could include 

configurations with partial incorporation of design modifications, allowing airlines to avoid 

concurrent major modifications on multiple engines. However, after that date, all design 

changes, whether for newly produced or existing airplanes, must be fully compliant with 

§ 25.939(a). 
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Our Decision 

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. We based this 

determination on additional information Boeing provided to support this petition and 

additional data provided to the FAA on August 18, 2015, which contained a summary of 

recent in-service ICI encounters that resulted in elevated engine vibrations. This 

information provides indication that the ICI logic that is now fully incorporated into the fleet 

is providing the expected benefit to the engines when operating in ICI conditions. The ICI 

logic, in conjunction with the current airplane flight manual ICI limitations and operating 

procedures (which by themselves are acceptable from a workload and complexity 

standpoint), result in no compromise in the level of safety for the airplane for the requested 

time period of this exemption. 

The Effect of Our Decision 

Our decision extends a time-limited exemption from § 25.939(a), at Amendment 25-40, to 

Exemption No. 11070 for Model 747-8 and 747-8F airplanes that have incorporated engine 

ice protection system modifications and associated AFM limitations. This grant of amended 

exemption provides a specific expiration date of September 30, 2016. 

The Grant of Amended Exemption 

In consideration of the foregoing, I find that a time-limited grant of exemption is in the 

public interest regarding 14 CFR 25.939(a) at Amendment 25-40. Therefore, pursuant to the 

authority contained in 49 U.S.C. 40113 and 44701 , delegated to me by the Administrator, I 

grant The Boeing Company an exemption until September 30, 2016, from the requirements 

of§ 25.939(a), as amended by Amendment 25-40. This amendment to the exemption is 

applicable to new production and in-service Boeing Model 747-8 and 747-8F airplanes 

incorporating modified electronic engine control software with engine ice protection system 

changes and associated AFM limitations. 

Boeing must show full compliance to 14 CFR 25.939(a), at Amendment 25-40, for newly 

produced Model747-8 and 747-8F airplanes in order to receive a certificate of airworthiness 

after September 30, 2016. Approval of design changes for in-service Model 747-8 and 

747-8F airplanes involving engine ice protection systems and associated AFM limitations 

made after September 30, 2016, must also fully comply with 14 CFR 25.939(a) at 

Amendment 25-40. 

All conditions and limitations of Exemption No. 11070 remain the same. This letter must be 

attached to, and is a part of, Exemption No. 11070. 

Sincerely, 

~i[~vJ~ Jolm P. Piccola 

Acting Manager, Transport Airplane Directorate 

Aircraft Certification Service