SouthwestAirlines Co. Alan Kasher Managing Director/Director ofOperations Regulatory Programs &Compliance 2702 Love Field Dr. P.O. Box36611, TOP-1DO Dallas, Texas 75235 (469) 603-0948

June 5, 2015

U.S. DepartmentofTransportation Docket Operations West Building Ground Floor, RoomW12-140 1200 NewJerseyAvenue, SE Washington, DC 20590 

# Southwesf.

Subject: Petition ofExemption- 14 CFR §121.629(b)- Operation in Icing Conditions

Dear Siror Madam:
In accordancewith the provisions ofTitle 14, Code ofFederal Regulations (14 CFR) §11.63 and §11.81, SouthwestAirlines Co. petitions for a limited Exemptionfrom 14 CFR §121.629(b). Specifically, Southwest requests an Exemption on the Boeing B737-700 and -800 "Next Generation" (B737NG) series aircraftfrom the requirementthat "No person maytake offan aircraftwhen frost, ice, orsnow is adhering tothewings", where the Original Equipment Manufacturer(OEM) has determined a "safe" zone within which cold soaked fuel frost (CSFF) is permissible, hasvisibly markedthe zone on thewing, and has placed an appropriate limitation in theAirplane Flight Manual (AFM) thatthe Federal AviationAdministration (FAA) has approved. Background Airframe icing in general is known to be a hazard to safe operation ofaircraft, especially on thewing. Wing surface texture changes can disrupt laminarairflowon thewing causing degradation of lift and increased stall speed, adversely affecting aircraft performance. Ice on thewing mayform in a particular set ofconditionsthat may include near orsub-freezing temperatures in combination with precipitation and/or high humidity (especiallyfog). Additionally, frost mayform in clear meteorological conditions on wing areas with underlying cold soakedfuel caused bycruise at high altitude followed by landing in a humid climate, a condition known as CSFF. Boeing has applied painted lines defining an area on the uppersurface ofthe wings on certain B737NG aircraft, where with certain other limitations; CSFF mayexistwith negligible impairment of performance. All Southwest B737-700 and -800 NG series aircraft have the lines definingthe permissible area ofCSFF painted on the upperwing surfaces. Boeing has issued specific "Miscellaneous Limitations" regarding CSFF in its FAA-approved AFM that setforth conditions underwhich takeoff is not permitted (see attachment 1). Ifthe listed limiting conditions are not present, i.e. even with CSFF presenton the wing tank upper surfaces, operation should be permissible absentthe existence ofotherspecified adverse conditions. Forexample, consider an airplanethat has arrived in a moderatetemperature, humid climate after a long-range high altitude cruise. Frost mayform in the limited area dueto cold fuel, butthe outside conditions are not otherwise conducive to icing, and Boeing's limitation would not preclude takeoff. FAA approval ofthe AFM provides the basis uponwhich operation with CSFF is permissible and should be allowed pursuantto 14 CFR 121.629 (b) which providesthat "Takeoffswith frost underthewing in the area ofthe fuel tanks may be authorized bytheAdministrator."Subject: Petition of Exemption- 14 CFR §121.629(b)- Operation in Icing Conditions June 5, 2015 2

The Applicable Regulations and ReliefSought Southwest seeks an exemption from 14 CFR §121.629(b)to permit operation with CSFFwithin a defined area ofthe wing's uppersurface. The exemption would be limited by Boeing'sAirplane Flight ManualMiscellaneous Limitations regarding CSFF that defines conditions underwhich takeoffwith CSFF is not permitted (attachment 1).
Reasonsforseekingthe reliefatthistime include: 1) In conjunction with NASA, the FAA has approved Boeing's conservative determination through aerodynamic analysis ofthe conditions underwhich operation with CSFF is and is not permitted. 2) Boeing's application ofpainted lines on the wing, which FAA also approved, definesthe area of acceptable CSFF. 3) The AFM limitation assures that operations are only permitted in certain instances ofcold soaked fuel; operations are notauthorized (without deicing) when airframe icing conditions otherwise exist. Grantingthe ExemptionWould NotAdversely Affect Safety Safetywill not be adversely impacted ifthe FAAgrantsthis petition because, by approving the Boeing AFM, FAA has concluded thatthe conditions underwhich operation with CSFF present is permitted on B737NG are sufficiently conservative and tested by Boeing and NASAto be safefortakeoff.
The requirements contained in thisAFM limitation prevent application on aircraftthat are noteligible. A visual inspection ofthe upperwing surface is required to ensurethat CSFF is not beyond the lines defining the boundaries ofthe cold soaked fuel frost area. To apply the revised B737NGAFM limitation for Cold Soaked Fuel Frost, the B737-NG must havethe "permissible" lines definingthe boundaries ofthe CSFF area on the upperwing. B737 Classic series aircraftdo not have lines defining a permissible CSFF area, which disqualifies application ofthe B737NG AFM limitationfor CSFF.
A Summaryofthis Petition that FAA Could Publish in the Federal Register
Petitioner: Affected Regulations: Summary of ReliefSought: SouthwestAirlines Co. 14 CFR 121.629(b)

FAA is requested to provide relieffrom the cited rule specifictothe operation of Boeing 737-600, -700, -800, and -900/-900ER ("NG") aircraftwith Cold Soaked Fuel Frost present in defined areas ofthe wing uppersurface, subjecttothe Miscellaneous Limitations applicable to Cold Soaked Fuel Frost provided in the FAA-approved Boeing Airplane Flight Manual. Granting this Exemption is in the public interest as it maintains an equivalent level ofsafety, because Boeing has conducted aerodynamic analyses that conservatively conclude the conditions underwhich safe operation is permissible. Conclusion
Forthe foregoing reasons, we respectfully request an Exemption from the requirements of 14 CFR §121.629(b) forCSFF limited by Boeing'sAFM conditions.Subject: Petition ofExemption- 14 CFR §121.629(b)- Operation in Icing Conditions June 5, 2015 3

Sincerely,

AK!js

cc: 

### L. Paul Kriner Ill, FAA, FLM James Hardgrove, FAA, APOI Craig Drew, VP Flight Ops Jeff Hamlett, DirAirOperationsAssurance Tim Leonard, DirProcedures Compliance and Ops Jim Stieve, Sr. MgrOperCert & Compliance Barry Brown, Associate General Counsel- Operations & Environment

## rti-IIOEIND• 737-600/-700/-800/-900 Airplane Flight Manual 

### REVISION HIGHLIGHTS
Revision 20 to D631A001.F01 dated 02-17-15.
The engineering developed and the FAA certification provided by Airplane Flight Manual (AFM) revisions are applicable and valid only for the airplane in its original Boeing delivery configuration as modified by the incorporation of approved Boeing service bulletins. With respect to any other modifications, it shall be the responsibility of the operator to obtain appropriate regulatory agency approval for application of the data provided by this AFM revision. 

### The purpose of this revision is to revise the cold soaked fuel frost limitation to simplify the limitaion.
The following changes comprise this revision:
PAGE CODE EXPLANATION ' Revision Approval

1 

### 143607 This page uniquely identifies the approval authority and the reference number for this revision. Log of Pages 1,2 F01

Section 1
14A 400X Revised to reflect pages changed in this revision.

Revised the cold soaked fuel frost limitation to simplify the limitation, eliminating the symmetry requirement and physical frost measurement.

D631A001.F01 Page 1

## rti-IIDEIND® 737-600/-700/-800/-900 Airplane Flight Manual



### Revision Approval



### This Revision Approval page may only be used in conjunction with a Log of Pages that refers to Reference Number 143607 

### in the code column for the Revision Approval page.

# ~~~



# r Manager, Seattle

# Air~tification FAA Transport Airplane Directorate Date 02-17-15

D631A001 Office,

Reference 143607 Revision Approval Page 1

### Units LB/F 

## f1_BDEIND• 737-600/-700/-800/-900 Airplane Flight Manual 

### Log of Pages
The following pages comprise the manual for Boeing airplane serial numbers listed on the Airplane Serial Number 

### & Appendix Effectivity Page.
Revision 20

Page Code Date Page Code Date Title Section 1 (Cont'd)
1 700 03-13-01 6A 4000 03-08-05 6B 4000 03-08-05 Revision Approval 6C 4000 01-06-05 6D 4000 10-13-05 

## * 1 143607 02-17-15 6E 4000 03-08-05 7 0001 05-17-11 Log of Pages 7A 4000 04-18-07 8 0001 02-27-09 

## * 1 F01 02-17-15 9 4000 11-20-02 

## * 2 F01 02-17-15 10 0001 04-16-01 11 07000 02-12-03 ASN & 

### App. Effectivity 12 0001 12-15-03 13 4002 09-11-03 1 F01 12-16-13 13A 4IIIB 09-11-03 14 CPDLC 03-19-12 App. Apl. & 

### AFM-DPI 

## * 14A 400X 02-17-15 15 4000 01-10-07 1 OF01 02-27-09 16 4000 09-25-03 2 OF01 12-16-13 17 4000 10-02-03 2A OF01 12-16-13 18 4000 09-25-03 3 4000 07-25-03 Section 2 Section 1 1 OF01 07-27-06 1 4002 03-24-05 2 4001 07-25-03 1A 4000 01-10-07 3 4000 04-16-01 2 OF01 04-17-02 4 4000 07-27-06 2A 1715 04-17-02 5 4000 07-26-07 3 4000 04-16-01 5A OF01 07-27-06 4 OF01 02-13-14 5B OF01 04-17-02 5 1550 06-20-01 5C 4000 09-12-02 5A 1715 04-17-02 6 4000 04-16-01 6 4000 01-06-05 7 0001 07-19-01 

## * - Revised Pages FAA Approved 02-17-15 D631A001.F01 Date 02-17-15 Page Code Section 2
8 4000 9 4000 10 4002 11 4001 11A 4001 11B 0001 12 4000 12A 4000 12B 0001 13 4001 13A 4000 14 

### 4000 15 4000 16 4001 17 4001
Section 3
1 4EIIIB 2 CPDLC 2A CPDLC 3 4001 4 4002 4A 4002 4B 4702 4C 4002 4D 4002 5 4IIIB 5A 4IIIB 5B 4IIIB 5C 4IIIB 6 4IIIB 7 4008 Date (Cont'd)
04-16-01 04-16-01 08-15-01 12-12-02 12-12-02 04-16-01 04-17-02 06-04-02 04-16-01 04-13-04 04-17-02 07-25-03 05-29-02 12-12-02 12-12-02

02-13-14 03-19-12 01-27-12 02-15-02 04-13-04 09-11-03 09-11-03 09-11-03 09-11-03 09-11-03 09-11-03 09-11-03 09-11-03 09-11-03 12-16-08

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### Revision 20 Page Code Date Section 3 (Cont'd)
7A 4009 06-17-10 7B 4ETOP 10-13-10 

## s 4000 10-06-03 SA 4000 10-06-03 SB 4000 10-06-03 9 4000 01-06-05 9A 4000 03-0S-05 9B 4000 03-0S-05 9C 4000 03-0S-05 9D 4000 10-13-05 10 0002 02-13-14 lOA 0001 02-13-14 11 4000 12-15-03 12 0001 04-16-01 13 0001 04-16-01 14 0001 10-16-01 15 0001 02-04-03
Section 4
1 467S 12-19-03 2 4ALTAP 12-16-13 3 0001 04-16-01 4 4ALTAP 12-16-13 4A WSRL 07-05-13 5 0001 04-16-01 6 4000 04-16-01 7 4000 04-16-01 

## s 0001 04-16-01 SA 4000 09-19-02 9 0001 04-16-01 9A 0001 04-16-01 10 4000 04-16-01 11 0001 04-16-01 12 4000 05-03-02 13 0001 04-16-01 14 0001 04-16-01 15 4000 03-14-02 16 0001 04-16-01 

### * - Revised Pages FAA Approved 02-17-15 

## rtl--BOEINO• 737-600/-700/-800/-900 Airplane Flight Manual



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17 00012 05-14-01 lS 17300 11-07-97 19 17000 11-07-97 20 17000 11-07-97 21 17000 11-07-97 22 17000 11-07-97 23 00000 04-16-01 23A 00900 05-17-11 24 4724 02-05-02

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# rp__aoE.ING" 737-600/-700/-800/-900 AIRPLANE FLIGHT MANUAL


### M I S C E L L A N E 0 U S L I M I T A T I 0 N S

COLD SOAKED FUEL FROST Takeoff with cold soaked fuel frost on the wing tank upper surfaces is not permitted if any of the following conditions are present: 1. The ambient air temperature is below +4°C, +39°F. 2. The tank fuel temperature is below -16°C, +3°F. 3. There is cold soaked fuel frost on the wing tank upper surfaces that is beyond the lines defining the permissible cold soaked fuel frost area. 4. There is precipitation or visible moisture (rain, snow, drizzle, or fog with less than 1 mile visibility).

Code 400X FAA APPROVED 

### 02-17-15 D631A001 Section 1 Page 14A