Subject: Petition for Exemption 

Reference: 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, United Airlines petitions for a limited Exemption from 14 CFR §121.629(b). Specifically, 

A4A requests an Exemption on the Boeing B737-600, -700, -800 and -900/-900ER "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 has approved. 

Background 

Airframe icing in general has long been 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 loss of lift and reduced stall speed, adversely affecting aircraft performance. Further, 

the weight of accumulated ice may present a weight and balance issue unknown to the crew 

and that cannot be accurately estimated from visual observation. 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 on a cold 

wing, particularly in areas with underlying cold soaked fuel as in the case of an airplane recently 

exposed to high altitude cruise conditions that has landed 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. Boeing has issued a new limitation in the AFM that sets forth conditions under 

which takeoff is not permitted with CSFF (attachment 1 ), stating that CSFF outside the painted 

limit lines, extremely cold fuel, or the presence of other common airframe icing conditions 

preclude takeoff in accordance with 14 CFR §121.629(b). However, if the above-listed limiting 
determination set forth in the Airplane Flight Manual, an FAA approved document. By approving 

the AFM, FAA provides the basis upon which operation with CSFF can be permitted if this 

petition is granted. 

The Applicable Regulations and Relief Sought 

We seek 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 Manual - Miscellaneous Limitations notation that defines conditions under which takeoff 

with CSFF is not permitted. 

Reasons for seeking the relief at this time include: 

1) 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, define the 

areas 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 FAA has concluded 

by approving the AFM that the conditions under which operation with CSFF present is permitted 

on B737NG by the AFM are sufficiently conservative and tested by Boeing 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. The B737NG 

AFM limitation for CSFF cannot be applied to a 737 Classic (1 00-500) series aircraft or B737NG 

aircraft that has not been delivered or later modified with the CSFF boundary lines. 
the FAA-approved Airplane Flight Manual when operations are not 

permitted. 

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. 

Steven Bastas 

Manager - Winter Operations 

United Airlines - 233 South Wacker Drive 

WHQAO -17th Floor I Chicago, IL 60606 

0 872-825-1209 I M 224-735-6029 

steve.bastas@ united.com