In the early days of aviation, it was a preferred practice to ‘foam the runway’ if an aircraft had a landing gear emergency. The thinking behind this practice was that if an aircraft had an emergency, fire retardant foam would be sprayed on the runway by emergency personnel to prevent sparks from igniting leaking fuel or the aircraft itself on arrival.
The recent belly landing and tragic crash of Jeju Air 2216 led many online to ask why the airport did not ‘foam the runway’ prior to landing.
This practice has been largely abandoned over the years. The FAA withdrew a circular about the practice way back in 1987. While ICAO still provides procedures on how to foam a runway, the practice is rarely used today. Here’s why:
Foaming The Runway Can Induce Unnecessary Risks
In earlier days of aviation, the concept of foaming the runway was seen as a best practice. Piston driven aircraft and airliners were slower. Runway length was typically not as much of a factor due to the relatively low speed approaches of the aircraft. Foaming the runway was seen as a way to prevent fires from starting.
The video below shows how firefighters deployed foam on the runway prior to a known arrival of an aircraft with a gear malfunction.
Aircraft were generally less reliable. Landing gear issues were more common and training on such scenarios were not as rigorous. Foaming was seen as the best option at the time but has been superseded by other approaches.
Foaming The Runway Is a Time Intensive Process
There are many difficulties with ‘foaming’ a runway. First, it is a lengthy process. A runway can be anywhere from one to three miles long. This means that it can take a lengthy time to deploy the fire retardant chemicals. Emergencies can happen fast.
While firefighting crews typically respond to an unexpected incident in less than 3 minutes, the time and coordination necessary to foam a runway in a coordinated manner with many vehicles would be much lengthier and time-consuming.
Foaming The Runway Requires Significant Chemicals
The amount of fire retardant necessary to ‘foam’ a runway can be significant. All airfields have a limited amount of fire vehicles and fire retardant chemicals. This means that some retardant that could be used to put out a fire after an incident would have already been disbursed prior to the incident. An FAA circular from 1966 highlights some of the risks with foaming the runway due to a landing gear malfunction. This circular was rescinded in 1987 by the FAA.
Advances in pilot training and aircraft safety
As modern aircraft have improved over time, landing gear and hydraulic systems have improved in robustness and reliability. This makes the likelihood of a landing gear malfunction much less common. While landing gear malfunctions still occur, they are relatively rare. Aircraft systems are more robust as well to reduce the likelihood of leaks and increase the amount of redundancies in case of a malfunction.
Additionally, pilot training has better emphasized the importance of fully diagnosing emergencies and utilizing alternate systems to deploy landing gear and flaps. This means that pilots are more comprehensive in their diagnosis and resolution of issues, lessening the frequency of landing with an unresolved issue that could require foaming the runway.
Improved Firefighting Techniques
Aircraft systems and pilot training play a large part in successfully resolving aircraft incidents safely. Firefighting techniques have also improved drastically over the years. Airport firefighters regularly train to meet modern response time requirements.
They are trained how to best approach an aircraft to most effectively fight a fire and keep passengers and crews safe. Firefighters also have better tools to spot ‘hot spots’ on a stricken aircraft and more precisely target a fire.
Foam Can Introduce Additional Complexities
There are a few other reasons why foaming a runway is no longer the preferred option in an aircraft landing emergency. Modern airliners have precise landing data to ensure a safe stopping margin when landing. This information is based on the approach speed, runway available, winds, and surface friction.
A foamed runway has the effect or reducing the surface friction verses a dry runway. That means that the landing distance on a foamed runway would be significantly longer. While all aircraft have landing data for wet and snowy runways, the type of foam used could vary by airport meaning that the precise friction on a runway may be indeterminate.
In any emergency, you want to control the variables. Foaming the runway can add additional complexity and unknown risk.
Lastly, many firefighting foams contain PFAS. These are chemicals known to cause harm to the human body and the environment. While the chemicals are still needed for actual firefighting, the usage of them have been limited in training to reduce harm and long-term environmental risk.
