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June 2, 2015

U.S. Department of Transportation Docket Operations 

### West Building Ground Floor, Room W12-140 1200 New Jersey Avenue, SE Washington, DC 20590 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, Alaska Airlines petitions for a limited Exemption from 14 CFR §121.629(b). Specifically, Alaska Airlines 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 inay 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 limitingconditions are not met, i.e. CSFF is present within the limit lines and other specified adverse

conditions do not exist, operation should be permissible. An example of such permissible operation would be an airplane that has arrived in a moderate temperature, humid climate after 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. Regulation 14 CFR 121.629 does not allow for any exception, including the OEM's safety 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 (100-500) series aircraft or B737NG aircraft that has not been delivered or later modified with the CSFF boundary lines.A Summary of this Petition that FAA Could Publish in the Federal Register

Petitioner: Alaska Airlines Affected Regulations: 14 CFR 121.629(b) Summary of Relief Sought: FAA is requested to provide relief from the cited rule when the OEM, Boeing allows operation of B737-600, -700, -800, and -900/-900ER "NG" aircraft with Cold Soaked Fuel Frost present in defined areas of the wing upper surface and states conditions in 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.

Sincerely,

0-- i Winkelma irector, Flight Operations Regulatory Compliance Alaska Airlines