# ~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 ofTransportation Docket Operations WestBuilding Ground Floor, Room F12-140 1200 NewJersey Avenue S.E. Washington DC 20590


### Dear SirorMadam, Subject: Petition for Exemptionto Title 14 Code of Federal Regulations (CFR) Part 25.863 )>

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### In accordance with the provisions ofTitle 14 Code ofFederal Regulation §11.61(b) The Boeing Company, herein petitions for an exemption from 14 CFR §25.863, the exemptionpetition only address 14 CFRPart 25.863, in accordance withthe agreement in FAA letter 1 06B-11-26, dated 2/7/2011.
Airlines have expressed an interest inusing the pre-PIP nozzle and plug on airplane line number 3762 and on. Consequently, Boeing has preparedthis exemptionpetition. 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 exemptionpetition is for re-application and has been revised to address FAA questions that were communicatedto Boeing inthe FAA Letter, "Review ofPetition LetterNo. RA-11-04847, dated 1/20/2012. Boeing requests the FAA to considerthe enclosed exemption petition.
The exemption, ifgranted, applies to the following airplanes when owned and/or operated by Boeing:


### Model

737


### ContactInformation:
John Hamilton VP, Regulatory Administration Boeing Commercial Airplanes P.O. Box 3707, M/C 03-37 Seattle, WA 98124-2207 

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e-mail: john.a.hamilton@Boeing.com

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Page2 U.S Department ofTransportation Docket Operations RA-12-02182


### The specific sections of 14 CFRfrom which we seek an exemption: Boeing is seeking relieffrom the following regulation for the main engine exhaustplug installation on the 737-600/-700/-700C/-800/-900/-900ER models: § 25.863 Flammablefluidfireprotection. (a) In each area where flammablefluids or vapors mightescape by leakage of a

fluidsystem, there must be means to minimize theprobability of ignition of thefluids andvapors, and,the resultant hazards 

## if ignition does occur. (b) Compliance withparagraph (a) of this section mustbe shown by analysis or tests, andthefollowing factors mustbe considered: (1) Possible sources and paths of fluid leakage, andmeans of detecting leakage.

(3) Possible ignitionsources, including electrical faults, overheating of equipment, andmalfunctioningof protective devices. 

### The extent ofreliefwe 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/- 900ERmodels uses a core exhaust nozzle andplug to control the flow ofthe exhaustgases 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 endto allow the engine vent airto 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 ofthe 314A2620-1 plug installation. Boeing is seeking relieffrom §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/orthe center vent tube. There are no drainage provisions in the 314A2620-1 plug installation. The plug surface temperatures can exceed the auto-ignition temperature ofengine oil and fuel. Consequently direct compliance for the 314A2620-1 plug installation cannotnow 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. AtLine No. 3762, Boeing introduced a new exhaust installation including a new plug that was compliantwith §25.863. However, the newtype design could not be approved with the 314A2620-1 plug installation as an interchangeable spare for the new exhaust. Consequently, installation ofthe 314A2620-1 plug is not allowed on 737-600/-700/-700C/-800/-900/-900ER models from Line No. 3762 and on. Boeing is seeking relieffrom the regulation via exemption to allow the installation.

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Page 3 U.S Department ofTransportation Docket Operations RA-12-02182

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 ofairplanes 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 ofthe spare engine kitto minimize the engine change time on the flightline. Operators have informed Boeingthat the interchangeability restriction will increase operational costs arising from the additional inventory control processes thatwill be needed, and potential delays ifthe correct exhaustpart number is not immediately available. These costs will eventually be passed onto 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 affectpublic safety based onthe features summarized below. The FAA-SACO agreed with a similar assessment in 2009. The airplane is protected from the effects ofa 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 ofthe plug to provide for ventilation flow. This opening is approximately 60 inches aft from the location where fluid would collect atthe forward end ofthe plug. The plug is shielded from the airplane surfaces along most ofits length by the exhaust nozzle, which is also considered fireproof. There is a heat shield directly above and aft ofthe. exhaustthatprotects the aft strut fairing. The heat shield is considered fireproof. Thelower surfaces ofthe wing within one nacelle diameter ofthe fire zone, including the control surfaces, are fire resistant. The vertical distance from the opening in the aft end ofthe 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 ofa tailpipe fire, the Boeing Flight Crew Operations Manual (FCOM) directs fuel-flow shutoffand motoring ofthe 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 ofthe engine that could result in evacuation ofthe oil system into the plug cavity will be indicated to the flight crew by a low oil pressure indicationPage4 U.S Department ofTransportation Docket Operations RA-12-02182

after a loss of 15-18 liters ofoil out ofa full engine oil tank capacity of20.2 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 ofhot surface ignition sources at the exhaust nozzle andplug as the engine cools Reduction ofair flow through the center venttube into the plug which will limit the intensity ofany fire already burning Minimization offlame impingement and heattransferto 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 notpossible due to a particular mode ofengine failure or inappropriate flight crew action, analysis shows ignition sources will not exist in the main fuel tank for a minimum of5 minutes of exposure to an oil fed tailpipe fire. During an oil fed tailpipe fire, temperatures within the main fuel tank ofthe affected wing will remain below the JetA auto-ignition temperature of440°F during a 5 minute exposure period. Thermal analysis shows a tailpipe fire will result in a maximum main tank lower inside skin temperature of401°F within the first 5 minutes ofexposure even ifthe engine is not motored to provide cooling flow. The minimum fuel quantity evaluated was 1400 lbs pertank. Attachment 1 contains a plot ofmaximum temperature with respect to time for this and other fuel quantities. The centertank is sufficiently far away to minimize exposure to a tailpipe fire. The investigation ofCOSP 2008-1396 did not report damage indicating significantheating ofthe center tank. While failure modes existthat would permit introduction offuel inside the plug, there have been no reports offuel leakage into the plug and all known tailpipe fires within the plug have been attributed to oil burning. A number oftailpipe 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 bythe flight and ground crews in the same manner as a traditional fuel-fed tailpipe fire occurring in the primary gas path. The risk ofinappropriate crew orpassenger response exists for any tailpipe fire and is not limited to a specific design of nozzle orplug. A tailpipe fire, regardless ofcause, will not adversely affect egress through forward doors orrear over-wing door on opposite side ofaircraft. The Boeing FlightAttendantManual (FAM) provides recommended egress procedures for a flight crew initiated evacuation. The FAM guidelines specify that the safety ofinside and outside conditions should be assessed before opening an exit. Ifan exit is unsafe, flight attendants are trained to redirectpassengers to other exits.

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Page 5 U.S Department ofTransportation Docket Operations 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 ofApril2011. Operation and installation ofthe 314A2620-1 plug installation onpost-Line No. 3762 airplanes is identical to the installations that have safely accumulated these hours/cycles. Summary ofPetition 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/-900ERmodel airplanes, Line No. 3762 and on. Request toWaive Publication and Comment In some cases, the FAA may waive the requirement for publication'and comment. One potential reason is thatthe reliefrequested is identical to previously granted exemptions. Given that the installation ofthe 314A2620-1 exhaustplug is currently operating on over 3,500 airplanes and has accumulated over 66 million hours and 35 million cycles as ofApril2011, Boeing requests that the FAA waive the requirement for publication and comment. Need to Exercise the Exemption Outside ofthe United States
737-600/-700/-700C/-800/-900/-900ER model airplanes from LineNo. 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 ofthe petitioned exemption outside ofthe United States.
Should you have questions orrequire additional information, please do not hesitate to contactthe 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 SupportEngineering (425) 717-3706, MC 04-AF FAX: (425) 294-9340 alj
Enclosures: 1) 737NG Main TankEngine Oil TailpipeFire Thermal Analysis

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