Southwest Airlines Co. 

Alan Kasher 

Managing Director /Director of Operations 

Regulatory Programs & Compliance 

2702 Love Field Dr. 

P.O. Box36611, TOP-1DO 

Dallas, Texas 75235 

(469) 603-0948 

June 5, 2015 

U.S. Department of Transportation 

Docket Operations 

West Building Ground Floor, Room W12-140 

1200 New Jersey Avenue, SE 

Washington, DC 20590 

Southwesf. 

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

Dear Sir or Madam: 

In accordance with the provisions of Title 14, Code of Federal Regulations (14 CFR) §11.63 and §11.81, 

Southwest Airlines Co. petitions for a limited Exemption from 14 CFR §121.629(b). Specifically, Southwest 

requests an Exemption on the Boeing B737-700 and -800 "Next Generation" (B737NG) series aircraft from 

the requirement that "No person may take off an aircraft when frost, ice, or snow is adhering to the wings", 

where the Original Equipment Manufacturer (OEM) has determined a "safe" zone within which cold 

soaked fuel frost (CSFF) is permissible, has visibly marked the zone on the wing, and has placed an 

appropriate limitation in the Airplane Flight Manual (AFM) that the Federal Aviation Administration (FAA) 

has approved. 

Background 

Airframe icing in general is known to be a hazard to safe operation of aircraft, especially on the wing. 

Wing surface texture changes can disrupt laminar airflow on the wing causing degradation of lift and 

increased stall speed, adversely affecting aircraft performance. Ice on the wing may form in a particular 

set of conditions that may include near or sub-freezing temperatures in combination with precipitation 

and/or high humidity (especially fog). Additionally, frost may form in clear meteorological conditions on 

wing areas with underlying cold soaked fuel caused by cruise 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 upper surface of the wings on certain B737NG 

aircraft, where with certain other limitations; CSFF may exist with negligible impairment of performance. 

All Southwest B737-700 and -800 NG series aircraft have the lines defining the permissible area of CSFF 

painted on the upper wing surfaces. Boeing has issued specific "Miscellaneous Limitations" regarding 

CSFF in its FAA-approved AFM that set forth conditions under which takeoff is not permitted (see 

attachment 1 ). If the listed limiting conditions are not present, i.e. even with CSFF present on the wing 

tank upper surfaces, operation should be permissible absent the existence of other specified adverse 

conditions. For example, consider an airplane that has arrived in a moderate temperature, humid climate 

after a long-range high altitude cruise. Frost may form in the limited area due to cold fuel, but the outside 

conditions are not otherwise conducive to icing, and Boeing's limitation would not preclude takeoff. FAA 

approval of the AFM provides the basis upon which operation with CSFF is permissible and should be 

allowed pursuant to 14 CFR 121.629 (b) which provides that "Takeoffs with frost under the wing in the 

area of the fuel tanks may be authorized by the Administrator." 
Subject: Petition of Exemption- 14 CFR §121.629(b)- Operation in Icing Conditions 

June 5, 2015 

2 

The Applicable Regulations and Relief Sought 

Southwest seeks an exemption from 14 CFR §121.629(b) to permit operation with CSFF within a defined 

area of the wing's upper surface. The exemption would be limited by Boeing's Airplane Flight ManualMiscellaneous Limitations regarding CSFF that defines conditions under which takeoff with CSFF is not 

permitted (attachment 1 ). 

Reasons for seeking the relief at this time include: 

1) In conjunction with NASA, the FAA has approved Boeing's conservative determination through 

aerodynamic analysis of the conditions under which operation with CSFF is and is not permitted. 

2) Boeing's application of painted lines on the wing, which FAA also approved, defines the area of 

acceptable CSFF. 

3) The AFM limitation assures that operations are only permitted in certain instances of cold soaked 

fuel; operations are not authorized (without deicing) when airframe icing conditions otherwise exist. 

Granting the Exemption Would Not Adversely Affect Safety 

Safety will not be adversely impacted if the FAA grants this petition because, by approving the Boeing 

AFM, FAA has concluded that the conditions under which operation with CSFF present is permitted on 

B737NG are sufficiently conservative and tested by Boeing and NASA to be safe for takeoff. 

The requirements contained in this AFM limitation prevent application on aircraft that are not eligible. A 

visual inspection of the upper wing surface is required to ensure that CSFF is not beyond the lines defining 

the boundaries of the cold soaked fuel frost area. To apply the revised B737NG AFM limitation for Cold 

Soaked Fuel Frost, the B737-NG must have the "permissible" lines defining the boundaries of the CSFF 

area on the upper wing. B737 Classic series aircraft do not have lines defining a permissible CSFF area, 

which disqualifies application of the B737NG AFM limitation for CSFF. 

A Summary of this Petition that FAA Could Publish in the Federal Register 

Petitioner: 

Affected Regulations: 

Summary of Relief Sought: 

Southwest Airlines Co. 

14 CFR 121.629(b) 

FAA is requested to provide relief from the cited rule specific to the operation of Boeing 737-600, -700, 

-800, and -900/-900ER ("NG") aircraft with Cold Soaked Fuel Frost present in defined areas of the wing 

upper surface, subject to the 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 of safety, because 

Boeing has conducted aerodynamic analyses that conservatively conclude the conditions under which 

safe operation is permissible. 

Conclusion 

For the foregoing reasons, we respectfully request an Exemption from the requirements of 14 CFR 

§121.629(b) for CSFF limited by Boeing's AFM conditions. 
Subject: Petition of Exemption- 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, Dir Air Operations Assurance 

Tim Leonard, Dir Procedures Compliance and Ops 

Jim Stieve, Sr. Mgr Oper Cert & 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 

Page 1 

Continued 
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 

Page Code Date 

Section 4 (Cont'd) 

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 

D631A001.F01 

Page Code 

Log of Pages 

Date 

Page 2 

Last Page 
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