Deicing operations include removing ice from aircraft, applying chemicals to prevent initial icing or further icing (anti-icing), and removing (and preventing) ice from airfield pavement (runways, taxiways, aprons, and ramps). Prior to departure, the removal of ice, snow, slush, or frost from an aircraft’s critical surfaces can be accomplished by mechanical means, using heat, using a heated fluid, using forced air, or a combination thereof. When frost, snow, or ice adheres to an aircraft surface, the surface must be heated or sprayed with pressurized fluid to remove the contaminant. Anti-icing on the ground is accomplished by applying a freezing point depressant to a surface either following deicing or in anticipation of subsequent winter precipitation; it is intended to protect the critical surfaces from ice adherence for a limited period of time. The fluid is capable of absorbing freezing or frozen precipitation until the fluid freezing point coincides with the ambient temperature. Once this fluid freezing point has been reached, the fluid can no longer protect the aircraft from ground icing conditions. During in-flight operations, an anti- icing system is expected to keep ice from forming in all but severe icing conditions and is accomplished with the use of engine bleed air, electro- thermal heaters, or fluid freezing point depressants. Table 1 describes the tools and processes used for ground deicing and anti-icing procedures on aircraft; table 2 describes systems found on aircraft for in-flight ice protection. FAA issues regulations, airworthiness directives, and other guidance and monitors industry compliance as part of its mission to ensure safe, orderly, and efficient air travel in the national airspace system. FAA regulations contain a number of parts, and different parts apply to aircraft based on their size and type and the activities they are used for. In this report we use the term “large commercial airplanes” to refer to those airplanes operating under part 121 of title 14 of the United States Code of Federal Regulations. Among other things, part 121 applies to air carrier operations involving turbojet airplanes or any airplane with a seating capacity of more than nine passenger seats or a maximum payload capacity of more than 7,500 pounds. We use the term “small commercial airplanes” to refer to those airplanes operating under part 135 of title 14. Among other things, part 135 covers certain commuter and on-demand operations on airplanes, other than turbojet powered airplanes, with nine passenger seats or less, and a payload capacity of 7,500 pounds or less. Some commuter and most air tour operators and medical services (when a patient is on board) fall under the purview of part 135. By “noncommercial airplanes,” we mean airplanes that are privately operated under part 91 of title 14. These types of operations are often referred to as “general aviation” and include, among other things, flights for recreation and training and certain business flights. Although noncommercial flights usually involve small aircraft, the definition we are using depends on the nature of the operation, not the size of the aircraft. In developing regulations, FAA follows the rulemaking process used by all federal agencies, which is established in the Administrative Procedure Act (APA). This act establishes procedures and broadly applicable federal requirements for informal rulemaking, also known as notice and comment rulemaking. This process is designed to provide the opportunity for public participation in rulemakings by submission of written comments and to ensure that all aspects of any regulatory change are fully analyzed before the change goes into effect. Starting early in a rulemaking, FAA may seek input from its Aviation Rulemaking Advisory Committee (ARAC), and during the course of a rulemaking it may conduct research related to the rulemaking. In addition, the APA generally requires agencies to publish a notice of proposed rulemaking in the Federal Register. During the public comment period that follows the publication of the proposed rule, interested parties may submit written comments, which FAA examines and may consider when making any changes before publishing the final rule. The final rule is then incorporated into the United States Code of Federal Regulations, but it may not take effect immediately. For example, FAA may phase in requirements over time or it may give industry time— sometimes several years—to implement changes. FAA can also issue airworthiness directives. An airworthiness directive is a legally enforceable rule that may apply to an aircraft or its parts, such as engines and propellers. FAA issues an airworthiness directive when it determines that (1) an unsafe condition exists in the product and (2) the condition is likely to exist or develop in other products of the same type design. NTSB investigates and reports on civil aviation accidents, which it defines as occurrences whereby a person suffers death or serious injury, or in which the aircraft receives substantial damage. FAA and NTSB also investigate aviation incidents, which NTSB defines as occurrences other than an accident associated with the operation of an aircraft that affects or could affect the safety of operations. FAA maintains an incident database generated by its investigations. NASA also administers a voluntary reporting system on aviation incidents, called the Aviation Safety Reporting System (ASRS). It contains voluntary reports, which are later de-identified, from pilots, controllers, maintenance technicians, and other operating personnel about human behavior that resulted in unsafe occurrences or hazardous situations. NASA seeks to avoid double counting of incidents by ensuring that multiple reports for a single incident are grouped together under that incident. Because ASRS reporting is voluntary, it is unlikely to cover the universe of safety events. It is also possible that ASRS incident data may overlap with FAA incident data because a single incident may be entered into FAA’s incident database by an FAA inspector and reported to ASRS by a pilot or bystander. However, the extent to which overlap occurs is unknown. When airlines and airports conduct deicing operations on aircraft and airfield pavement, the large amounts of chemicals used for deicing operations may drain off airport facilities to nearby rivers, lakes, streams, and bays and can have major impacts on water quality. In August 2009, the Environmental Protection Agency (EPA) issued a proposed rule on the use of deicing fluids at airports. According to EPA, the proposed rule would require 218 airports to collect spent deicing fluid and treat the associated wastewater, and 6 major airports would likely need to install centralized deicing pads to comply with the rule. Additionally, some airports would be required to reduce the amount of ammonia discharged from urea-based airfield pavement deicers or use more environmentally friendly airfield deicers that do not contain urea. EPA plans to issue a final rule in December 2010. According to NTSB’s aviation accident database, from 1998 to 2009 one large commercial airplane was involved in a nonfatal accident after encountering icing conditions during flight and five large commercial airplanes were involved in nonfatal accidents related to snow or ice on runways. Although there have been few accidents, FAA and others recognize that incidents are potential precursors to accidents. Data on hundreds of incidents that occurred during this period reveal that icing, contaminated runways, and other winter weather conditions pose substantial risk to aviation safety. FAA’s database of incidents includes 120 incidents related to icing, contaminated runways, taxiways, or ramps, or other winter weather conditions involving large commercial airplanes that occurred from 1998 through 2007. These data covered a broad set of events, such as the collision of two airplanes at an ice-covered gate, and an airplane that hit the right main gear against the runway and scraped the left wing down the runway for about 63 feet while attempting to land with ice accumulation on the airplane. During this same time period, NASA’s ASRS received over 600 icing and winter weather-related incident reports involving large commercial airplanes. These incidents reveal a variety of safety issues such as runways contaminated by snow or ice, ground deicing problems, and in-flight icing encounters. These incidents thus also suggest that risks from icing and other winter weather operating conditions may be greater than indicated by NTSB’s accident database and by FAA’s incident database. FAA officials point out that there is no defined reporting threshold for ASRS reports and because they are developed from personal narrative, they can be subjective. However, these officials agree that the ASRS events must be thoroughly reviewed and evaluated for content to determine the relevancy to icing and the extent and severity of the safety issue. The contents of the ASRS data system also demonstrate the importance of aggregating data from all available sources to understand a safety concern. See table 3 for the number of icing and winter weather-related incident reports from ASRS for large commercial airplanes. While our review focused on large commercial airplanes, small commercial airplanes and noncommercial airplanes experienced more icing-related accidents and fatalities than did large commercial airplanes from 1998 to 2007, as shown in table 4. They did so largely because, compared to large commercial airplanes, small commercial airplanes and noncommercial airplanes (1) may be performance-limited and therefore operate for longer periods at lower altitudes that more frequently have icing conditions, (2) have a higher icing collection efficiency due to their smaller scale, (3) are more greatly impacted by ice as a result of their smaller scale, (4) tend to have deicing equipment (e.g., pneumatic deicing boots) rather than fully evaporative anti-icing equipment, and (5) may not be approved for flight in known icing conditions. If an airplane is not approved for flight in icing conditions, it may either not have an ice protection system installed, or it may have an ice protection system that is not certified. As part of its Air Transportation Oversight System (ATOS), FAA assesses large carriers’ ground deicing programs to ensure that they meet relevant safety regulations.