~DEIND John A. Hamilton 

Lead Administrator 

Regulatory Administration 

Commercial Airplanes 

The Boeing Company 

P.O. Box 3707 MC 03-56 

Seattle, WA 98124-2207 

MAY 212012 

RA-12-02182 

U.S. Department of Transportation 

Docket Operations 

West Building Ground Floor, Room F12-140 

1200 New Jersey Avenue S.E. 

Washington DC 20590 

Dear Sir or Madam, 

Subject: Petition for Exemption to Title 14 Code of 

Federal Regulations (CFR) Part 25.863 

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In accordance with the provisions of Title 14 Code ofFederal Regulation 

§ 11.61(b) The Boeing Company, herein petitions for an exemption from 14 CFR 

§25.863, the exemption petition only address 14 CFR Part 25.863, in accordance 

with the agreement in FAA letter 1 06B-11-26, dated 2/7/2011. 

Airlines have expressed an interest in using the pre-PIP nozzle and plug on 

airplane line number 3762 and on. Consequently, Boeing has prepared this 

exemption petition. Note that this exemption petition only addresses 14 CFR 

Part 25.863, in accordance with the agreement in the FAA letter 106B-11-26. 

This exemption petition is for re-application and has been revised to address 

FAA questions that were communicated to Boeing in the FAA Letter, "Review 

ofPetition Letter No. RA-11-04847, dated 1/20/2012. Boeing requests the FAA 

to consider the enclosed exemption petition. 

The exemption, if granted, applies to the following airplanes when owned and/or 

operated by Boeing: 

Model 

737 

Contact Information: 

John Hamilton 

VP, Regulatory Administration 

Boeing Commercial Airplanes 

P.O. Box 3707, M/C 03-37 

Seattle, WA 98124-2207 

I Type 

e-mail: john.a.hamilton@Boeing.com 
r[J_BDEIND 

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U.S Department of Transportation 

Docket Operations 

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The specific sections of 14 CFR from which we seek an exemption: 

Boeing is seeking relief from the following regulation for the main engine 

exhaust plug installation on the 737-600/-700/-700C/-800/-900/-900ER models: 

§ 25.863 Flammablefluidfire protection. 

(a) In each area where flammable fluids or vapors might escape by 

leakage of a fluid system, there must be means to minimize the probability 

of ignition of the fluids and vapors, and ,the resultant hazards if ignition 

does occur. 

(b) Compliance with paragraph (a) of this section must be shown by 

analysis or tests, and the following factors must be considered: 

(1) Possible sources and paths of fluid leakage, and means of 

detecting leakage. 

(3) Possible ignition sources, including electrical faults, overheating 

of equipment, and malfunctioning of protective devices. 

The extent of relief we are seeking, and the reason we are seeking the relief: 

Extent ofRelief 

The CFM56-7B engine installation on the 737-600/-700/-700C/-800/-900/-

900ER models uses a core exhaust nozzle and plug to control the flow of the 

exhaust gases from the engine. The CFM56-7B engine incorporates a center vent 

tube that exhausts air into the plug cavity. The plug has a 4.8 inch opening in the 

aft end to allow the engine vent air to exhaust overboard. The engine also 

incorporates a drain for the main bearing aft oil sump that discharges into the 

plug cavity. There are no designed drainage provisions for the plug cavity of the 

314A2620-1 plug installation. 

Boeing is seeking relief from §25.863 (a),(b)(1),(b)(3) as it applies to the internal 

cavity ofthe 314A2620-1 plug installation on certain 737-600/-700/-700C/-800/-

900/-900ER airplanes. Engine oil and/or fuel can be directed to the plug cavity 

by the aft sump drain and/or the center vent tube. There are no drainage 

provisions in the 314A2620-1 plug installation. The plug surface temperatures 

can exceed the auto-ignition temperature of engine oil and fuel. Consequently 

direct compliance for the 314A2620-1 plug installation cannot now be shown to 

§25.863 (a),(b)(l),(b)(3). The 314A2620-1 plug installation was previously 

found compliant with §25.863 (a),(b)(l),(b)(3) in error. 

At Line No. 3762, Boeing introduced a new exhaust installation including a new 

plug that was compliant with §25.863. However, the new type design could not 

be approved with the 314A2620-1 plug installation as an interchangeable spare 

for the new exhaust. Consequently, installation of the 314A2620-1 plug is not 

allowed on 737-600/-700/-700C/-800/-900/-900ER models from Line No. 3762 

and on. Boeing is seeking relief from the regulation via exemption to allow the 

installation. 
~DEING 

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U.S Department of Transportation 

Docket Operations 

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Public Interest 

Exemption from §25.863 (a),{b)(1),(b)(3) for the 314A2620-1 plug installation 

on Line No. 3762 and on would be in the public interest. The inability to use the 

314A2620-1 plug on a sub-group of airplanes within an airline operator's fleet 

creates a significant interchangeability issue. There are currently over 7,000 of · 

the 314A2620-1 plugs in service operation. Typically the exhaust is installed as 

part of the spare engine kit to minimize the engine change time on the flightline. 

Operators have informed Boeing that the interchangeability restriction will 

increase operational costs arising from the additional inventory control processes 

that will be needed, and potential delays if the correct exhaust part number is not 

immediately available. These costs will eventually be passed on to the public. 

Removing the restriction will allow greater flexibility and increased efficiency 

for the operator to better serve the public. 

Safety 

Exemption from §25.863 (a),{b)(1);(b)(3) for the 314A2620-1 plug installation 

on Line No. 3762 and on would not adversely affect public safety based on the 

features summarized below. The FAA-SACO agreed with a similar assessment 

in 2009. 

The airplane is protected from the effects of a potential fire within the exhaust 

plug by the following design and construction features: 

The plug is considered fireproof. There is a 4.8 inch diameter opening in 

the aft end of the plug to provide for ventilation flow. This opening is 

approximately 60 inches aft from the location where fluid would collect 

at the forward end of the plug. 

The plug is shielded from the airplane surfaces along most of its length by 

the exhaust nozzle, which is also considered fireproof. 

There is a heat shield directly above and aft of the. exhaust that protects 

the aft strut fairing. The heat shield is considered fireproof. 

The lower surfaces of the wing within one nacelle diameter of the fire 

zone, including the control surfaces, are fire resistant. 

The vertical distance from the opening in the aft end of the plug to the aft 

fairing is 11 inches; to the undersurface ofthe wing is 36 inches. The 

horizontal distance to the wing rear spar is 48 inches. 

The area is surrounded by the engine primary gas path and turbine frame. 

In the event of a tailpipe fire, the Boeing Flight Crew Operations Manual 

(FCOM) directs fuel-flow shutoff and motoring of the engine to keep 

flames away from the airplane and cool the engine. 

COSP 2008-1396 and other tailpipe fire events were reviewed by the 

Engineering Investigation Board (EIB) and received "not safety" determinations 

based on the supporting rationale documented above. 

Failures of the engine that could result in evacuation of the oil system into the 

plug cavity will be indicated to the flight crew by a low oil pressure indication 
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U.S Department of Transportation 

Docket Operations 

RA-12-02182 

after a loss of 15-18 liters of oil out of a full engine oil tank capacity of 20.2 

liters. The FCOM instructs the crew to perform an engine shutdown for low oil 

pressure indication. Risks associated with continued oil flow during windmilling 

after engine shutdown are mitigated by: 

Removal of hot surface ignition sources at the exhaust nozzle and plug as 

the engine cools 

Reduction of air flow through the center vent tube into the plug which 

will limit the intensity of any fire already burning 

Minimization of flame impingement and heat transfer to the surrounding 

structure due to cooling flow through the engine primary gas path while 

in flight 

Cooling flow through the engine primary gas path is provided on ground by 

engine motoring. When engine motoring is not possible due to a particular mode 

of engine failure or inappropriate flight crew action, analysis shows ignition 

sources will not exist in the main fuel tank for a minimum of 5 minutes of 

exposure to an oil fed tailpipe fire. 

During an oil fed tailpipe fire, temperatures within the main fuel tank of the 

affected wing will remain below the Jet A auto-ignition temperature of 440°F 

during a 5 minute exposure period. Thermal analysis shows a tailpipe fire will 

result in a maximum main tank lower inside skin temperature of 401 °F within the 

first 5 minutes of exposure even if the engine is not motored to provide cooling 

flow. The minimum fuel quantity evaluated was 1400 lbs per tank. Attachment 

1 contains a plot of maximum temperature with respect to time for this and other 

fuel quantities. 

The center tank is sufficiently far away to minimize exposure to a tailpipe fire. 

The investigation ofCOSP 2008-1396 did not report damage indicating 

significant heating of the center tank. 

While failure modes exist that would permit introduction of fuel inside the plug, 

there have been no reports of fuel leakage into the plug and all known tailpipe 

fires within the plug have been attributed to oil burning. 

A number of tailpipe fires have occurred in service, however only a few have 

resulted in visible damage to the airplane. 

A potential fire in the plug cavity will be identified and addressed by the flight 

and ground crews in the same manner as a traditional fuel-fed tailpipe fire 

occurring in the primary gas path. The risk of inappropriate crew or passenger 

response exists for any tailpipe fire and is not limited to a specific design of 

nozzle or plug. A tailpipe fire, regardless of cause, will not adversely affect 

egress through forward doors or rear over-wing door on opposite side of aircraft. 

The Boeing Flight Attendant Manual (F AM) provides recommended egress 

procedures for a flight crew initiated evacuation. The F AM guidelines specify 

that the safety of inside and outside conditions should be assessed before opening 

an exit. If an exit is unsafe, flight attendants are trained to redirect passengers to 

other exits. 
· tzi--aoE.ING 

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U.S Department of Transportation 

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RA-12-02182 

The installation is currently operating on over 3,500 airplanes and has 

accumulated over 66 million hours and 35 million cycles as of April2011. 

Operation and installation of the 314A2620-1 plug installation on post-Line No. 

3762 airplanes is identical to the installations that have safely accumulated these 

hours/cycles. 

Summary of Petition 

Petitioner: Boeing Commercial Airplanes 

Section of 14 CFR affected: 14 CFR 25.863(a), (b)(1), (b)(3) 

Description ofReliefSought: To permit installation ofthe 314A2620-1 exhaust 

plug on 737-600/-700/-700C/-800/-900/-900ER model airplanes, Line No. 3762 

and on. 

Request to Waive Publication and Comment 

In some cases, the FAA may waive the requirement for publication 'and 

comment. One potential reason is that the relief requested is identical to 

previously granted exemptions. Given that the installation of the 314A2620-1 

exhaust plug is currently operating on over 3,500 airplanes and has accumulated 

over 66 million hours and 35 million cycles as of April2011, Boeing requests 

that the FAA waive the requirement for publication and comment. 

Need to Exercise the Exemption Outside of the United States 

737-600/-700/-700C/-800/-900/-900ER model airplanes from Line No. 3762 and 

on are anticipated to be operated in many foreign countries. To provide for 

maximum efficiency and flexibility for foreign operators, Boeing requests that 

the FAA allow the use of the petitioned exemption outside of the United States. 

Should you have questions or require additional information, please do not 

hesitate to contact the undersigned or Debra Dean at debra.a.dean@boeing.com 

or (425) 717-1165. 

Very truly yours, 

~~?JW~---., 2012.05.21 . { 14:22:20 -07'00' 

Brady J. Mitchell 

RA Program Manager, Product Support Engineering 

(425) 717-3706, MC 04-AF 

FAX: ( 425) 294-9340 

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Enclosures: 1) 737NG Main Tank Engine Oil Tailpipe Fire Thermal 

Analysis 
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