Explained: What foaming a runway means and the controversy surrounding it

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What is a foam path?

A foam path is an aviation safety practice of spreading a layer of fire suppression foam on an airport runway prior to an emergency landing. Following a crash-landing, liquids leaking from the aircraft, which are not yet burning, start evaporating, thereby resulting in forming an air-vapour mixture that is flammable or even highly explosive. In such cases, extinguishing foam is used preventively and the liquid is covered with a foam carpet as a vapor barrier.

Airport fire brigades create a foam carpet in order to secure an emergency landing if the landing gear of an aircraft is not extended or is unstable. This is done in order to suppress sparking and burning of any aircraft metals due to friction with the runway surface.

The concerns surrounding use of foam paths

Although originally it was thought that foam paths would prevent fires, the practice is now discouraged. The United States Federal Aviation Administration (FAA) recommended foam paths for emergency landings in around 1966, but withdrew that recommendation in 1987, although not barring its use.

In 2002, a circular recommended against using pre-foaming except in certain circumstances. Explaining the operational issues related to using foam paths, the FAA stated that reliability of information on the landing techniques to be used relating to wind and visibility conditions, pilot experience and skill, visual and radio aids available and the aircraft operational problems should be considered before using the technique.

Mumbai airport officials sprayed foam on the runway to prevent fire as the aircraft made a belly landing

Moreover, data available from a study of emergency landings made with, and without, the application of foam show that no significant reduction is achieved in the risk of fire or in the extent of damage by the foaming of runways. Also, from all that is known of the fire suppression qualities of foam and the scale research tests, it is clear that a foamed runway would have no appreciable effect on the fire hazard of fuel vapours in the atmosphere over the foam.

The International Civil Aviation Organization, too, does not recommend foaming the runway in its Airport Services Manual, stating that the effectiveness of runway foaming is not fully substantiated by the real evidence of operational incident studies.