~BEING 

Y1-D300-AC-15-416 

November 19,2015 

Docket Management Facility 

U.S. Department of Transportation 

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 of Federal Regulations (CFR) §25.341(a) in 

Support of FAA Project ST00279MC-T (ODA Project 192) for the Model767-2C 

The Boeing Company respectfully submits the enclosed Petition for Exemption from Title 14 Code of Federal 

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 of the 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 of the 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 conventional transport aircraft. The design of the boom and local 

attachment structure provides sufficient and appropriate structural capability as it is designed to the static gust 

requirements of the KC-10A as well as USAF-approved military gust requirements. The boom design provides 

the same or better structural capability as the KC-1 OA 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 petitioner requests that this Petition for Exemption not be delayed by the public 

process, which includes publication of the subject petition. If this exemption is not granted, it could lead to 

delays in the delivery of the STC modified 767-2C to the USAF at a critical time of need. The STC modified 

767-2C approved aircraft will not be eligible to receive a civil airworthiness approval or standard certificate of 

airworthiness. It is intended that the aircraft will be maintained as a public use aircraft only for the life of the 

product. However, if the FAA chooses to solicit public comment, the petitioner respectfully requests the FAA to 

use the paragraph on the last page of the enclosure entitled "Summary to be Published in the Federal Register". 

Granting of this exemption petition is kindly requested by May 19, 2016. 

If you have any questions, please do not hesitate to contact the 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 of Federal Regulations 

§25.341(a) Arndt. 25-86 

cc: Joel Ligon (FAA Wichita MCO Program Manager) 

JeffDuven (FAA Transport Airplane Directorate Manager) 

Enclosure to Yl-D300-AC-15-416 

Pagel of5 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.341(a) Arndt 25-86 for 

the Aerial Refueling Boom (ARB) 

Name and Address of the Petitioner 

David Hom 

The Boeing Company 

6001 S. Air Depot, MIS R7-53 

Oklahoma City, OK 73135 

Section(s) of the Regulations from which Relief is sought: 

14 CFR § 25.341(a) Tuned Discrete Gust 

(a) Discrete Gust Design Criteria. The airplane is assumed to be subjected to symmetrical 

vertical and lateral gusts in level flight. Limit gust loads must be determined in accordance 

with the following provisions: 

(1) Loads on each part of the structure must be determined by dynamic analysis. The analysis 

must take into account unsteady aerodynamic characteristics and all significant structural 

degrees of freedom including rigid body motions. 

(2) The shape of the gust must be: 

for 0 5. s 5. 2H 

where--

s =distance penetrated into the gust (feet); 

Uds =the design gust velocity in equivalent airspeed specified in paragraph (a)(4) of this 

section; and 

H =the gust gradient which is the distance (feet) parallel to the airplane's flight path for the 

gust to reach its peak velocity. 

(3) A sufficient number of gust gradient distances in the range 30 feet to 350 feet must be 

investigated to find the critical response for each load quantity. 

(4) The design gust velocity must be: 

Utb = Urtf[i'g(H I 350) 116 

where--

Urer= the reference gust velocity in equivalent airspeed defined in paragraph (a)(5) of this 

section. 

F g = the flight profile alleviation factor defined in paragraph (a)( 6) of this section. 

(5) The following reference gust velocities apply: 

(i) At the airplane design speed V c: Positive and negative gusts with reference gust velocities 

of 56.0 feet/sec EAS must be considered at sea level. The reference gust velocity may be 

reduced linearly from 56.0 ft/sec EAS at sea level to 44.0 ftlsec EAS at 15000 feet. The 

reference gust velocity may be further reduced linearly from 44.0 ftlsec EAS at 15000 feet to 

Enclosure to Yl-D300-AC-15-416 

Page2of5 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.34l(a) Amdt 25-86 for 

the Aerial Refueling Boom (ARB) 

26.0 ftlsec ES at 50000 feet. 

(ii) At the airplane design speed V0 : The reference gust velocity must be 0.5 times the value 

obtained under Sec. 25.341 (a)(5)(i). 

(6) The flight profile alleviation factor, Fg, must be increased linearly from the sea level 

value to a value of 1.0 at the maximum operating altitude defmed in Sec. 25.1527. At sea 

level, the flight profile alleviation factor is determined by the 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.:U mum l UJr.(!f - o..u w ezg t 

Maximum Zero Fuel Weight 

Rl = Maximum Take -off Weight ; 

Zmo =Maximum operating altitude defined in Sec. 25.1527. 

(7) When a stability augmentation system is included in the analysis, the effect of any 

significant system nonlinearities should be accounted for when deriving limit loads from 

limit gust conditions. 

The Extent ofReliefSou~bt and Reason(s) 

Regulation Requires: Relief is Necessary because: 

14 CFR § 25.341(a) Gust analysis with dynamic tuned Applying this requirement to the aerial 

Amendment 25-86 discrete gust with gradient refueling boom would drive significantly 

distances ranging from 30 feet to increased gust loads resulting in impractical 

350 feet redesign of the boom and local attachment 

structure. 

Description of Issue 

Application of 14 CFR § 25.34l(a), Tuned Discrete Gust (TDG) to the STC modified 767-2C Aerial 

Refueling Boom (ARB) would result 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 of Federal 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 by the 

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 of the tuned 

discrete criteria, as was done with conventional transport aircraft. Tuned discrete gust criteria has not been 

used for prior boom design on the KC-10A or KC-135. 

Prior to Amendment 86, static gust was the discrete gust requirement in 14 CFR § 25.341. The replacement 

of static gust with tuned discrete gust in 14 CFR § 25.341 (a) at Amendment 86 was to provide for 

hannonization of the discrete gust requirements with the Joint Aviation Requirements (JARs). Tuned discrete 

gust was incorporated into the Code of Federal Regulations so that the requirements would be common and 

Applicants would not have 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 of increasing safety as stated in the 

Preamble to Amendment 86, "The objective was to achieve common requirements for the certification of 

transport airplanes without a substantive change in the level of the safety provided by the regulations." 

Tuned discrete gust simulates the aircraft being hit with an extreme single discrete gust, with gust velocities 

backed out from the static gust fonnula using aircraft cg accelerations that occur once in 70,000 flight hours. 

This gust velocity is then coupled with the worst possible gust frequency. Loads using this type of criteria are 

more significantly affected for boom-type structure than for conventional transport 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 of the 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 or evaluated on military aircraft and the load effects of this 

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 

of some modem alloys that were implemented on the STC modified 767-2C. All modem alloys were selected 

to have equivalent or better properties than the original alloys. The critical frequencies of the first natural 

bending modes of the two booms are very similar. 

Enclosure to Yl-D300-AC-l5-4l6 

Page 4 of5 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.341(a) Amdt 25-86 for 

the Aerial Refueling Boom (ARB) 

The expected usage and gust environment ofthe STC modified 767-2C and KC-10A booms are very similar. 

The KC-1 OA Fleet has an extensive service history with over 34 years and 1.5 million flight hours (59 

aircraft). In that time, there have been no incidents of recorded boom damage due to turbulence. 

The STC modified 767-2C boom and local attachment structure is designed to both the 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 or better structural capability as the KC-10A boom. Thus, 

the STC modified 767-2C boom design provides sufficient and appropriate structural capability needed for 

USAF operations. 

Statement ofPublic Interest 

Application of 14 CFR § 25.341(a) at Amendment 86 would cause significant modification to the STC 

modified 767-2C boom that is utilized only for military missions and has no civil utility. Additionally, the 

redesign of the 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 to the KC-46A prior to delivery to the USAF. If the relief is not 

granted, it could lead to delays in the delivery of the KC-46A to the USAF at a critical time of need. It 

remains in the public's interest to grant Boeing an exemption to I 4 CFR § 25.34 I (a) for the STC modified 

767-2C aerial refueling boom and local attachment structure. 

Statement of No 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 gust related 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 petitioner requests that this Petition for Exemption not be delayed by the 

public process, which includes publication of the subject petition. The STC modified 767-2C with an aerial 

refueling boom will be converted to the KC-46A prior to delivery to the USAF. The KC-46A is for exclusive 

military use and will not be eligible for a standard civil airworthiness certificate. Due to the STC modified 

767-2C being a uniquely military aircraft, specific public comment should be withheld to avoid additional 

assessment of the petition. 

Privileges of the Exemption Outside the United States 

Not requested 

Enclosure to Yl-D300-AC-15-416 

Page 5 ofS 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.341(a) Amdt 25-86 for 

the Aerial Refueling Boom (ARB) 

Conclusion 

The Boeing position is that tuned 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 

of the KC-lOA boom in addition to the fact that the STC modified 767-2C boom and local attachment 

structure is designed to both the KC-lOA static gust requirements and USAF-approved military gust 

requirements provides justification for an exemption of 14 CFR § 25.341(a). 

Based on the rationale above, Boeing hereby requests FAA issuance of an exemption for 14 CFR § 25.341 (a) 

Amendment 25-86 for the boom and its local attachment structure for the FAA Project No. ST00279MC-T -

Model STC modified 767-2C. 

Summary to be Published in the Federal Register 

PETITIONER: The Boeing Company 

SECTION OF 14 CFR AFFECTED: 14 CFR § 25.341(a) 

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 of the 

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 conventional transport aircraft. The design of the boom 

and local attachment structure provides sufficient and appropriate structural capability as it is designed to the 

static gust requirements of the KC-10A as well as USAF-approved military gust requirements. The boom 

design provides the same or better structural capability as the KC-1 OA boom which has an excellent safety 

record. The petitioner requests an exemption from 14 CFR § 25.341(a) for the STC modified 767-2C ARB 

and its local attachment structure.