“Foaming the runway” used to be part of the standard response for emergency landings where aircraft structures were likely to contact the runway at touchdown, such as when landing gear failure is suspected or confirmed. However, this has not been common practice for quite some time.
In the U.S., Advisory Circular 150/500-4, Foaming of Runways, was cancelled in the late 1980s. The International Civil Aviation Organization still explains how the procedure should be carried out in their Airport Services Manual, but the environmental impact of the best types of foam for this purpose requires those who still want to have the capability to invest in “protein-based” foam, which is both more expensive and less effective.
Fire-retardant foam is still highly useful when fighting aircraft fires, but again, there are serious concerns regarding the biodegradability of the “aqueous film-forming foam” that has been used in this application for decades. So-called “fluorine-free foams” are being developed to try to address these problems, but the newer foam is not necessarily as effective as that which its advocates hope to replace.
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