Aircraft deicing fluids are required to remove frozen precipitation from aircraft prior to flight, ensuring mission capability in winter conditions. Without effective removal of frozen precipitation, lift and control might be compromised and safety of flight is jeopardized. A problem with conventional fluids in use today, however, is that the primary component is propylene glycol (PG), which can exhibit a high biochemical oxygen demand (BOD) in receiving waters when it degrades. Thus the waste fluid can either threaten aquatic life or impede the effectiveness of waste water treatment processes, depending on where runoff from airfield deicing operations is directed. Some newer deicing fluid formulations feature the reduction or elimination of PG to assuage the BOD impact and reduce related runoff handling and permitting costs.
The objective of this demonstration was to investigate whether one reduced PG aircraft deicing fluid, EcoFlo (and later EcoFlo II), was effective at deicing military aircraft while having no negative effects on flight performance, operational safety, and aircraft materials.
EcoFlo and EcoFlo II have both been tested for compliance with Society of Aerospace Engineers (SAE) Aerospace Material Specification (AMS) 1424G, the commercial specification covering aircraft deicing fluids, and EcoFlo had been marketed for commercial aircraft use. A deicing fluid transfers heat to aircraft surfaces to either melt or soften frost, ice, and snow, allowing it to run off the aircraft. The fluid is heated to approximately 180°F to increase the melting/de-bonding effectiveness. Also, pressurized application of the fluid provides mechanical force to abrade and dislodge frozen substances. It is critical that the fluid contributes to freezing point depression when mixed with the melted contamination so that nothing will refreeze on the aircraft.
Prior to the demonstration involving deicing with EcoFlo on operational Air Force aircraft, two laboratory evaluations were performed. The first consisted of observing the compatibility of EcoFlo with materials likely to be found on military aircraft but not commercial aircraft (i.e., not covered by SAE AMS 1424G). For most of the materials tested, EcoFlo was shown to either have no impact or no impact more significant than that of the baseline fluid, which is a conventional PG fluid. A few cases were identified where EcoFlo did not perform as anticipated; these instances were marked for future evaluation should the fluid be considered for aircraft featuring those specific materials.
The second laboratory evaluation involved testing in a wind tunnel. Some previously reduced PG deicing fluids showed a tendency to leave a residue that both obscured visibility through windows or observation ports and left surfaces excessively slippery, hindering post flight inspection and maintenance. The project team determined that a wind tunnel evaluation might be suitable prior to investing the time and effort in a full aircraft demonstration. Surfaces exposed to the fluid were submitted to airflow consistent with takeoff velocities and then tested for impeded visibility and slipperiness. Although this evaluation was a simple approximation and could not duplicate the complex airflows encountered by various parts of an aircraft, it provided some indication that EcoFlo was likely to act similarly to conventional PG fluids and not leave a significant residue.
Prior to the full demonstration, the manufacturer of EcoFlo informed the project team that they were planning to market a new formulation, EcoFlo II (containing more PG, but still featuring a lower BOD than conventional PG fluids), and eventually discontinue EcoFlo. The project team considered the limited information available on the proprietary formulation and determined that it was unlikely that EcoFlo II would perform worse than EcoFlo in any of the laboratory evaluations already completed. Therefore, EcoFlo II was acquired for the full scale demonstration.
The full demonstration, using EcoFlo II, was carried out at Joint Base McGuire-Dix-Lakehurst. Maintenance personnel evaluated EcoFlo II for deicing effectiveness, including time, quantity of fluid, and labor required to thoroughly remove frozen precipitation on KC-135 aircraft. For comparison, a second aircraft was deiced with conventional PG fluid. A test flight crew checked for any inflight performance impacts attributable to the fluid, and then the maintenance crew performed post flight evaluations.
The experienced maintenance crew observed that the EcoFlo II effectively deiced the aircraft in an effective time frame and used a quantity of fluid typical for that type of aircraft with a given amount of frozen precipitation. However, because of rapidly changing weather conditions, a one-to-one, quantitative comparison to the conventional PG operation was inconclusive (the PG operation was likely aided by radiant heat when the skies cleared).
Flight characteristics were not impacted after the aircraft was deiced, although windows and viewing ports were obscured by fluid residue. Also, after the flight, aircraft surfaces were observed to be extremely slippery and a fall hazard for post flight inspection and maintenance. These factors led the onsite evaluation team to discontinue any further application of fluid (effectively ending the demonstration) and conclude that the EcoFlo II was not suitable for deicing on KC-135 aircraft.
EcoFlo II (as with EcoFlo) was formulated to reduce BOD impact while not affecting aircraft flight and maintenance operations (i.e., by not leaving slippery, blurry residue). Unfortunately, EcoFlo II still showed these negative effects during this specific event. If this was an anomaly, the factors leading to this unexpected performance must be understood and controlled. Otherwise, the fluid must be reformulated to reliably prevent residue issues before implementation can be considered.