Which procedure increases holding time when de-icing/anti-icing an airplane using a two-step process?

Using a two-step process for de-icing or anti-icing an airplane, the procedure that increases holding time involves applying heated type one fluid followed by cold type two fluid.

Type one fluid is designed to remove ice and snow from the aircraft surface while providing anti-icing protection. When heated, it becomes more effective at melting existing ice and snow. The application of heated type one fluid ensures that the aircraft surface is clean and free of contaminants. Following this, applying cold type two fluid provides a protective layer. Type two fluid is designed to remain on the aircraft longer and provides extended anti-icing protection due to its higher viscosity and lower freeze point compared to type one fluid.

The sequence of using heated type one fluid creates a warm surface that helps to prevent immediate ice reformation, thus enhancing the holding time of the cold type two fluid that is applied afterward. This two-step process, with the ideal temperature dynamics, maximizes the effectiveness of the anti-icing fluids, allowing for a longer time during which the aircraft can remain protected from ice accumulation.

In contrast, the other options do not effectively promote increased holding time due to their temperature profiles or fluid properties.