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56 CHAPTER 4 Increased Use of Spot Deicing for Aircraft Frost Removal Introduction The primary benefit of using spot deicing is a reduction in the amount of glycol used to achieve aerodynamically clean air- Deicing for Frost Removal craft wings prior to takeoff, compared to the amount used in Frost occurs when aircraft surfaces cool below 0°C (32°F) treating an entire upper wing surface. Reduced glycol con- due to radiation effects, and water vapor in the air sublimates sumption leads to lower fluid purchasing costs, lower fluid on the aircraft surfaces. Aircraft frost deicing (defrosting) with recovery costs, and reduced environmental impact. deicing fluids generally consists of a one-step deicing approach. Another benefit of spot deicing is a significant reduction in Defrosting is usually performed using a heated mixture of deic- defrosting time (to as short as 10 minutes, depending on air- ing fluid sprayed in a sweeping motion using a fan shaped noz- craft size, extent of frost coverage and ambient conditions). zle spray pattern. Holdover times are not required if the frost This reduced time leads to greater efficiencies in the use of deic- is not active. ing and other airport facilities. At remote deicing facilities, Frost conditions typically affect aircraft that are parked out- where aircraft are deiced with engines running, reduced engine side overnight. Thus, frost deicing activities are a concentrated run-time lowers fuel burn and its related carbon emissions, effort to deice aircraft prior to their first departure of the day. and lowers aircraft operating costs. A survey conducted in 2004 indicated approximately one third Several other relevant features of spot deicing for frost of all aircraft de/anti-icing activities worldwide occur in frost removal are: conditions (see Figure 16). In recent years, air carriers have begun to examine different · Additional operator and flight crew training is required to ways for deicing aircraft in frost conditions, as morning deic- implement this procedure; ing events can be very disruptive to operations. At airports with · Adoption of this procedure requires closer checking and centralized deicing facilities, the aircraft first pushes back from inspections by qualified personnel; and the gate, taxies to the designated deicing pad or facility, is · Conventional ground deicing equipment, suitable for nor- defrosted, and then taxies to the runway threshold for takeoff. mal defrosting usage, can be used to perform spot deicing for frost removal. Spot Deicing for Frost Removal Objective The term "Spot Deicing for Frost Removal" is defined as the use of deicing fluids to treat small affected aircraft wing upper The objective of this task was to gain a better understanding surfaces areas (patches of frost that are typically 20% of wing of the current practices employed for spot deicing for frost upper surface area) to remove (non-active) frost that may have removal, quantify its potential benefits, and provide tools for formed during a ground overnight stay. The entire wing is not decision makers to determine whether this procedure is suit- treated; however, both wings are treated symmetrically, regard- able for their operation. less if they both require defrosting. If any frost is observed on The objective was met by completing the following the leading edge of the wings, it must be removed. Depending activities: on ambient temperature and precipitation conditions, the wing may not require anti-icing. If the wing is not anti-iced, · Conducting a literature review of current government and then holdover times do not apply. industry regulations, guidance material, and standards to