# ~BEING

Y1-D300-AC-15-416 November 19,2015
Docket ManagementFacility U.S. Department ofTransportation 1200 New Jersey Avenue, S.E. West Building Ground Floor Room W12-140 Washington, DC 20590 The Boeing Company 6001 S. Air Depot Oklahoma City, OK 73135

Subject: Petition for Exemption from Title 14 Code ofFederal Regulations (CFR) §25.341(a) in Support ofFAA Project ST00279MC-T (ODA Project 192) for the Model767-2C The Boeing Company respectfully submits the enclosed Petition for Exemption from Title 14 Code ofFederal Regulations (CFR) §25.341(a) Arndt. 25-86 from the Certification Basis for FAA Project ST00279MC-T (ODA Project 192) for the Model 767-2C. The enclosure provides the details ofthe petition in accordance with 14 CFR §11.81.
DESCRIPTION OF RELIEF SOUGHT: Application of 14 CFR § 25.341(a) to the STC modified 767-2C aerial refueling boom (ARB) would drive significantly increased loads resulting in impractical redesign ofthe boom and local attachment structure. The boom is unique military structure. The tuned discrete gust requirements of 14 CFR § 25.341(a) were derived for conventionaltransport aircraft. The design ofthe boom and local attachment structure provides sufficient and appropriate structural capability as it is designed to the static gust requirements ofthe KC-10A as well as USAF-approved military gustrequirements. The boomdesignprovides the same orbetter structural capability as the KC-1OA boom which has an excellent safety record. The petitioner requests an exemption from 14 CFR § 25.34l(a) for the STC modified 767-2C ARB and its local attachment structure. As stated in 14 CFR §11.87, the petitionerrequests that this Petition for Exemptionnotbe delayed by the public process, which includes publication ofthe subjectpetition. Ifthis exemption is not granted, it could lead to delays in the delivery ofthe STC modified 767-2C to the USAF at a critical time ofneed. The STC modified 767-2C approved aircraft will notbe eligible to receive a civil airworthiness approval or standard certificate of airworthiness. Itis intended that the aircraft will be maintained as a public use aircraft only for the life ofthe product. However, ifthe FAA chooses to solicitpublic comment, the petitionerrespectfully requests the FAA to use the paragraph onthe lastpage ofthe enclosure entitled "Summaryto be Published in the Federal Register". Granting ofthis exemptionpetition is kindly requestedby May 19, 2016. Ifyou have any questions, please do not hesitate to contactthe undersigned. cerely,


## Y Mark G. allow ODA-501296-CE Certification Coordinator M/C OFA-E07 Telephone: Mobile: 425-237-8316 425-980-9816 Telephone: Facsimile: 405-582-8908 405-582-8257 Enclosure: Petition for Exemption from Title 14 Code ofFederal Regulations §25.341(a) Arndt. 25-86

cc: Joel Ligon (FAA WichitaMCO Program Manager) JeffDuven (FAA Transport Airplane Directorate Manager)-IEnclosure to Yl-D300-AC-15-416 Pagel of5 

### Petition for Exemption from Title 14 Code ofFederal Regulations§ 25.341(a) Arndt 25-86 for the Aerial Refueling Boom (ARB)

Name and Address ofthe Petitioner 

### David Hom The Boeing Company 6001 S. Air Depot, 

### MIS R7-53 Oklahoma City, OK 73135 Section(s) ofthe Regulations from which Reliefis sought: 

### 14 CFR § 

### 25.341(a) Tuned Discrete Gust (a) 

### Discrete GustDesign Criteria. The airplane is assumed to be subjected to symmetrical vertical and lateral gusts in level flight. Limit gust loads mustbe determined in accordance withthe following provisions: 

### (1) Loads on eachpart ofthe structure mustbe determinedby dynamic analysis. The analysis musttake into account unsteady aerodynamic characteristics and all significant structural degrees offreedom including rigid bodymotions. 

### (2) The shape ofthe gustmust be:



### for 0 

### 5. s 

### 5. 

### 2H
where-- s =distancepenetrated into the gust (feet); Uds =the design gust velocity in equivalent airspeed specified inparagraph (a)(4) ofthis section; and H =the gust gradient which is the distance (feet) parallel to the airplane's flight pathfor the gust to reach its peakvelocity. (3) A sufficientnumber ofgust gradient distances inthe range 30 feet to 350 feet mustbe investigatedto find the critical response for each load quantity. (4) The design gustvelocity must be:


### Utb = 

### Urtf[i'g(H I350) 116 

### where-- Urer= the reference gustvelocity in equivalent airspeed defined inparagraph (a)(5) ofthis section. 

### F

g 

### = the flight profile alleviation factor defined inparagraph (a)(6) ofthis section. (5) The following reference gust velocities apply: (i) Atthe airplane design speed Vc: Positive and negative gusts withreference gust velocities of56.0 feet/sec EAS mustbe considered at sea level. The reference gustvelocity maybe reduced linearly from 56.0 ft/sec EAS at sealevel to 44.0 ftlsec EAS at 15000 feet. The reference gustvelocity may be further reduced linearly from 44.0 ftlsec EAS at 15000 feet toEnclosure to Yl-D300-AC-15-416 Page2of5 

### Petition for Exemption from Title 14 Code ofFederalRegulations§ 25.34l(a) Amdt 25-86 for theAerial Refueling Boom (ARB)
26.0 ftlsec ES at 50000 feet. 

### (ii) Atthe airplane design speed V0 : 

### The reference gust velocity mustbe 0.5 timesthe value obtained under Sec. 25.341 (a)(5)(i). (6) The flight profile alleviation factor, 

### Fg, mustbe increased linearly from the sealevel value to a value of 1.0 atthe maximum operating altitude defmed in Sec. 25.1527. At sea level, the flight profile alleviation factor is determinedbythe following equation: 

### F1 = 

### 0.5(Fp+

### F,.) where-- 

# z

F =1- mo •

gz 

### 250000' 

# F.,.**=~R Tan(** 

# >IRy,;'}

Maximum Landing Weight 

## Rl =

### ~~ . '1"'-l- ,# r;rr
. 

### h ; 

### lrla.:Umum l UJr.(!f

- 

### o..u w 

### ezg t
Maximum Zero Fuel Weight 

### Rl

## = Maximum Take -offWeight ;

Zmo 

### =Maximumoperating altitude defined in Sec. 25.1527. (7) When a stability augmentation system is included inthe analysis, the effect ofany significant systemnonlinearities should be accounted for whenderiving limit loads from limit gust conditions.

TheExtent**ofReliefSou~bt** 

### andReason(s) Regulation Requires: Reliefis Necessarybecause: 14 CFR 

### § 25.341(a) Gust analysis with dynamic tuned Applying this requirement to the aerial Amendment 25-86 discrete gust with gradient refueling boomwould drive significantly distancesranging from 30 feetto increased gust loads resulting in impractical 350 feet redesign ofthe boom and local attachment structure.


### Description ofIssue Application of 14 CFR § 25.34l(a), TunedDiscrete Gust (TDG) tothe STC modified 767-2C Aerial Refueling Boom (ARB) wouldresult in significantly increased loads, causing impractical redesign oftbe boom and local attachment structure.Enclosure to YI-D300-AC-15-416 Page 3 of5 

### Petition for Exemption from Title 14 Code ofFederal Regulations§ 25.341(a) Amdt 25M86 for the Aerial Refueling Boom (ARB)
Aerial refueling aircraft were not considered when tuned discrete gust criteria were originally derived bythe Joint Aviation Authority. Tuned discrete gust was intended for conventional transport aircraft and used conventional transport aircraft accelerations to back out gust velocities using the static gust loads fonnula. In addition, aerial refueling aircraft were not evaluated for the load effects or economic impact ofthe tuned discrete criteria, as was done with conventional transport aircraft. Tuned discrete gust criteriahas notbeen used for prior boom design onthe KC-10A orKC-135.
Priorto Amendment 86, static gust was the discrete gust requirement in 14 CFR 

### § 25.341. The replacement ofstatic gust with tuned discrete gust in 14 CFR 

### § 25.341(a) at Amendment 86 wasto provide for hannonization ofthe discrete gust requirements with the Joint Aviation Requirements (JARs). Tuned discrete gust was incorporated into the Code ofFederal Regulations so that the requirements would be common and Applicants would nothave to comply with multiple discrete gust criteria. The change from static gust to tuned discrete gust was for hannonization and was not done with the goal ofincreasing safety as stated in the Preambleto Amendment 86, "The objective was to achieve common requirements for the certification of transport airplanes without a substantive change in the level ofthe safety provided by the regulations."
Tuned discrete gust simulates the aircraft beinghit with an extreme single discrete gust, with gust velocities backed out from the static gust fonnula using aircraft cg accelerations that occuronce in 70,000 flight hours. This gust velocity is then coupled with the worstpossible gust frequency. Loads using this type ofcriteria are more significantly affected for boom-type structurethan for conventionaltransport aircraft structure (wing, fuselage, empennage). Because TDG criteria derives gust velocities based on aircraft cg accelerations, the accelerations for structure far away from the cg, which create the majority ofthe load, have large variations that are analysis-driven and not validated by fleet data. In addition, the boom structure's constant spanwise
mass and stiffness properties cause load to be more affected by tip accelerations, thus increasing the loads significantly higher than past successful design practice. Conventional transport aircraft structure do not have this effect as the distributed mass and stiffness is significantly lower at the tip and increases towards the root, thus reducing the load effect from the high tip accelerations.
As tuned discrete gust criteria were not created for orevaluated on military aircraft and the load effects ofthis criteria are significantly higher for boom-type structure, this criteria is not appropriate for an aerial refueling boom, which is unique military structure.
Structural Capability
The STC modified 767-2C boom baseline is the KC-lOA. The KC-IOA and STC modified 767-2C booms are structurally similar. They have the same cross sectional area and the same basic materials, with the exception ofsome modem alloys that were implemented on the STC modified 767-2C. All modem alloys were selected tohave equivalent orbetterproperties than the original alloys. The critical frequencies ofthe first natural bending modes ofthe two booms are very similar.Enclosure to Yl-D300-AC-l5-4l6 Page 4 of5 

### Petition for Exemption from Title 14 Code ofFederal Regulations§ 25.341(a) Amdt 25-86 for the Aerial Refueling Boom (ARB)
The expectedusage and gust environment ofthe STC modified 767-2C and KC-10A booms are very similar. The KC-1 OA Fleethas an extensive service history with over 34 years and 1.5 million flight hours (59 aircraft). In thattime, there have been no incidents ofrecorded boom damage due toturbulence.
The STC modified 767-2C boom and local attachment structure is designed to boththe static gust requirements used for the KC-10A, in addition to USAF-approved military gust requirements. The STC modified 767-2C boom design provides the same orbetter structural capability as the KC-10A boom. Thus, the STC modified 767-2C boom design provides sufficient and appropriate structural capabilityneeded for USAF operations.
Statement ofPublic Interest Application of 14 CFR § 25.341(a) at Amendment 86 would cause significant modification tothe STC modified 767-2C boom that is utilized only for military missions and has no civil utility. Additionally, the redesign ofthe boom and local attachment structure would be impractical and provide no net benefit in the configuration and no commensurate increase in safety.
The STC modified 767-2C will be converted tothe KC-46A priorto deliveryto the USAF. Ifthe reliefis not granted, it could lead to delays in the delivery ofthe KC-46A to the USAF at a criticaltime ofneed. It remains in the public's interest to grant Boeing an exemptionto I 4 CFR 

### § 25.34I(a) for the STC modified 767-2C aerial refueling boom and local attachment structure.
Statement ofNo Adverse Effect on Safety Existing aircraft with installed booms such as the KC-IOA have a long safety history. The KC-lOA was certified in 1981 and the aircraft fleet has 1.5 million flight hours with no gustrelated damage affecting the boom. The STC modified 767-2C and KC-10A booms are structurally very similar. The STC modified 767- 2C boom and local attachment structure is designed to both the KC-IOA static gust criteria as well as USAFapproved military gust criteria. Thus applying the later gust criteria of 14 CFR 

### § 25.341(a) for tuned discrete gust does not add additional safety. Request to Waive Publication and Comment
As allowed in 14 CFR 

### §11.87, the petitionerrequests that this Petition for Exemption not be delayed bythe public process, which includes publication ofthe subject petition. The STC modified 767-2C with an aerial refueling boom will be converted to the KC-46A priorto delivery to the USAF. The KC-46A is for exclusive military use and will notbe eligible for a standard civil airworthiness certificate. Due to the STC modified 767-2C being a uniquely military aircraft, specific public comment should bewithheld to avoid additional assessment ofthe petition. Privileges ofthe Exemption Outside the United States
NotrequestedEnclosure to Yl-D300-AC-15-416 Page 5 ofS 

### Petition for Exemption from Title 14 Code ofFederal Regulations§ 25.341(a) Amdt 25-86 for the Aerial Refueling Boom (ARB)

Conclusion The Boeing position is thattuned discrete gust criteria in 14 CFR § 25.341(a) was derived for conventional transport aircmft and is not appropriate for the STC modified 767-2C aerial refueling boom as the boom is unique military structure. The STC modified 767-2C boom similarity to the KC-lOA boom, the safe history ofthe KC-lOA boom in addition to the fact thatthe STC modified 767-2C boom and local attachment structure is designed to both the KC-lOA static gustrequirements and USAF-approved military gust requirements providesjustification for an exemption of 14 CFR § 25.341(a).
Based onthe rationale above, Boeinghereby requests FAA issuance ofan exemption for 14 CFR § 25.341(a) Amendment 25-86 for the boom and its local attachment structure for the FAA ProjectNo. ST00279MC-T

- Model STC modified 767-2C.

Summary to bePublished in the Federal Register
PETITIONER: The Boeing Company
SECTION OF 14 CFRAFFECTED: 14 CFR § 25.341(a)
DESCRIPTION OF RELIEF SOUGHT: Application of 14 CFR 

### § 25.341(a) tothe STC modified 767-2C aerial refueling boom (ARB) would drive significantly increased loads resulting in impractical redesign ofthe boom and local attachment structure. The boom is unique military structure. The tuned discrete gust requirements of 14 CFR § 25.341(a) were derived for conventionaltransport aircraft. The design ofthe boom and local attachment structure provides sufficient and appropriate structural capability as itis designed tothe static gust requirements ofthe KC-10A as well as USAF-approved military gustrequirements. The boom design provides the same orbetter structural capability as the KC-1OA boom whichhas an excellent safety record. The petitionerrequests an exemption from 14 CFR 

### § 25.341(a) for the STC modified 767-2C ARB and its local attachment structure.