Potential Fire Hazard Not Know At Initial Certification

The FAA has issued a Special Airworthiness Information Bulletin for TKS de-icing fluid due to a potential flammability hazard. At this time, this airworthiness concern is not considered an unsafe condition that would warrant an airworthiness directive action.

In prior certifications of TKS systems on board aircraft, the issue of fluid flammability was not a concern; the fluid was simply considered to be non-flammable. However, recent testing has shown that the fluid is in fact flammable under certain conditions.

Per 14 CFR §23.863(b)(2), it is appropriate to consider the flammability characteristics of the specific fluid in question. In 2008, flammability testing of TKS fluid was documented by the FAA Technical Center in Report No. DOT/FAA/AR-TN08/9. The findings of the Technical Center report are that the TKS fluid is flammable only under very specific conditions:

• Sustained surface ignition will sometimes occur if a pool of fluid is heated to approximately 150°F and an ignition source is introduced. Above approximately 150°F the ignition is self-extinguishing. However, sustained surface ignition will occur if a pool of fluid is heated to approximately 250°F and an ignition source is introduced.
• A spray mist will ignite when exposed to a flame, but is not self-sustaining when the ignition source is removed.
• A spray mist will undergo “sporadic ignitions” confined to small areas when exposed to a spark, but is not self-sustaining.

It was determined that drip or stream directed onto a hot surface will not igniteIn short, the fluid is only self-sustainingly flammable when allowed to both pool and heat. Further, a spray mist is only flammable in the presence of a sustained ignition source. In essence the report supports the argument that it is appropriate in certain conditions to treat the fluid as non-flammable.

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