Laboratory Testing of Aircraft Anti-Icing Fluid Rehydrated Gel Residues 2007-01-3303

Gel residues occur as the result of repeated anti-icing fluid application that leaves a powdery film upon dryout that, when rehydrated, can swell up to over 600 times its weight. When these gels collect on aircraft flight control surfaces in aerodynamically quiet areas and freeze, they give rise to reduced performance, increased stick force, slowed rotation and have caused jammed flight controls. Laboratory tests have been developed to simulate the gel formation by drying out fluids and rehydrating them. However, by their complex nature, much variation is seen between test results from different laboratories and the results are not yet considered by fluid users.

Testing carried out at AMIL on different fluids with different test methods has led to a more reproducible results and a potential classification of fluids based on their gel formation potential (GFP). It was found that complete dryout of the fluid, steady immersion, plate etching, wait times, oven temperature, and number of fluid immersions are important factors to the reproducibility of the test method. While, bubbles in the test sample, fluid dilutions, fluid viscosity and weight of the dryout residues had little effect on the tests results. From this study, a classification of the fluids into three categories is proposed: (1) high GFP, (2) high GFP that rinses off and (3) low GFP. Finally, the effect of Type I rinses and runway deicing fluids on gel residues was also examined.