Fluid flammability for TKS fluid

Fluid flammability for TKS fluid

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. As a result, the concerns of 14 CFR, part
23, § 23.853(e), § 23.863, and § 23.1365(c) should be appropriately addressed.
In 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.
Aviation Safety
April 5, 2010
SUBJ: Flammable Fluid Considerations for TKS Fluid
This is information only. Recommendations aren’t mandatory.
This Special Airworthiness Information Bulletin (SAIB) alerts type certificate, amended type
certificate, and supplemental type certificate applicants of an airworthiness concern regarding the
issue of fluid flammability for TKS fluid.
At this time, this airworthiness concern is not considered an unsafe condition that would warrant an
airworthiness directive action under Title 14 of the Code of Federal Regulations (14 CFR part 39).
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 document is available at
http://www.fire.tc.faa.gov/pdf/TN08-9.pdf. 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.

A drip or stream directed onto a hot surface will not ignite.

We recommend that all type certificate, amended type certificate, and supplemental type certificate
applicants assess the pertinent regulations (14 CFR, part 23, §23.853(e), §23.863, and §23.1365(c))
for their TKS system and take any appropriate action. Specifically:

14 CFR, part 23, §23.853(e), which requires lines, tanks, and other equipment containing
flammable fluids not be installed in passenger compartments unless shielded, isolated, or
otherwise protected such that the fluid is not a hazard.

14 CFR, part 23, §23.863, which requires minimization of the probability of ignition of fluids
and vapors for each area where flammable fluids or vapors could escape.

14 CFR, part 23, §23.1365(c), which requires main power cables be separated from TKS fluid
lines or be shrouded by electrically insulated flexible conduct or equivalent, in addition to the
normal cable insulation.
In summary:

TKS anti-icing fluid requires consideration of flammability characteristics in order to
determine its appropriate classification. FAA testing has revealed that the fluid must be
considered as flammable under certain conditions. Specifically, TKS fluid must be considered
flammable when fluid pooling may occur under conditions that may then elevate the
temperature of the pool to a level that would support sustained combustion.

TKS fluid must also be considered flammable when conditions could present a situation
where a fine spray is directed onto a sustained flame source.

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