Chapter 4 - Preventative Measures and Deicing Procedures

Failed Fluid Recognition

88.  A fluid is considered failed when it is no longer able to absorb frozen precipitation. Under these circumstances it must be assumed that the contamination is adhering to the critical surfaces.

89.  Failed fluids can be difficult to recognize in that a layer of clear ice may have formed under the fluid. This clear ice can usually only be detected by a tactile inspection. A failed fluid will usually loose all its glossiness and resemble a dulled crystalline appearance. While snow fall on a wing may be readily apparent, the clear ice that may have formed underneath is not. Snow that has accumulated on a wing on top of de/anti-ice fluids means the fluid has failed and will not "blow off" on the takeoff roll. Similarly, Type I fluid when used alone, can refreeze in a matter of a few minutes after the holdover time has expired under certain precipitation conditions (especially freezing drizzle and freezing rain). The appearance is of a dulled rough coating of frost.

90.  Upon recognition of a failed fluid the aircraft must return for further de/anti-icing or take-off delayed until the weather improves and the contamination melts.