FOAMING OF RUNWAYS...definitive answers to:
This cert alert gives updated AFFF user guidelines in the following areas:
1. Aqueous Film Forming Foam (AFFF) - less than 3% Concentration
AFFF in concentrations less than 3% is not acceptable to the FAA for use on airports.
The 1% concentrate that is available should not be used in ARFF applications because of the difficulty in consistently providing an accurate mixture. Any attempt to use 1% foam would necessitate the installation of a computer-controlled system and each load would have to be checked carefully. There are other means of proportioning but they are not accurate at low percentage proportioning settings. Experience and testing have shown there is no consistency between different loads. Also, at low concentration, there is no room for error on the fire ground. If a mixture is discharged on the lean side, the result is plain water being applied to a fuel fire. The opposite of lean can be problematical also, because at 2% (only 1% off), you are consuming concentrate at twice the designed rate.
2. Use of Alcohol Type Foams
The FAA does not approve the use of alcohol type foams in ARFF vehicles on airports and part 139 does not provide for substituting Aqueous Film Forming Foam (AFFF) with alcohol type foams.
Alcohol type foams are typically used by city and industrial fire departments because they are effective on both hydrocarbons, such as gasoline, and polar solvents such as alcohol. They have to carry only one type of foam on their trucks if they use alcohol type foams. These foams are labeled AFFF/ATC or Alcohol Resistant AFFF, which gives airport operators and firefighters the impression that the foam is okay for airport use. We are aware of several airport ARFF stations using alcohol type foams because the foam was ordered using city fire department specifications for ATC/AFFF.
The following problems are associated with the use of alcohol type foams on an airport. Alcohol type foams are usually not compatible with AFFF currently in use at airports, and ARFF vehicles cannot proportion alcohol foams correctly without changes in the mechanical proportioning systems. Also, a special additive to the alcohol foam can produce, over time, a scale that can form in and obstruct the metering valves on truck foam systems.
3. ARFF Foaming of Runways for Emergency Landings
The FAA does not recommend the foaming of runways for emergency landings and warns against the practice with any foam other than “Protein” foam. Fluroprotein foam, film forming fluroprotein foam, and aqueous film forming foam are not considered suitable for runway foaming operations due to their short drainage time. It is recommended that ARFF personnel decline to foam a runway when requested by a pilot because they do not have the specialized equipment and protein foam
The effectiveness of runway foaming is not fully substantiated by the real evidence of operational incident studies. Neither the International Fire Service Training Association (IFSTA) nor the National Fire Protection Association (NFPA) recommends the practice. The International Civil Aviation Organization (ICAO) Airport Services Manual Part 1, Rescue and Fire Fighting, Third Edition - 1990, contains a chapter (Chapter 15) on foaming runways for emergency landings. The chapter addresses the theoretical benefits from foaming runways, but then describes the shortcomings of those benefits. It also describes operational problems that should be evaluated to determine the feasibility of foaming a runway.
Some of the problems are as follows:
* The difficulty of determining for certain the type of emergency that would lend itself to the practice such as the position and condition of landing gear.
* The time element available for accomplishing the production and distribution of the foam covering that may take up to an hour or more.
* The 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.
* The foam-making capability and adequacy of the equipment available. Airports not having adequate equipment should not attempt to lay a foam blanket. If the runway is to be foamed, it is essential that additional supplies of foam are available and the ability of the ARFF service to deal with any concurrent or subsequent aircraft accident must be assured.
* The effect the foam laying and clean-up operations will have upon the aircraft movements at the airport and how this will affect the safety of all aircraft operations in progress.
* The weather conditions during and immediately after the laying of a foam blanket. Foam should not be laid during heavy rain or snowfall conditions.
Techniques of runway foaming differ, depending on the numerous variables involved. Without the proper equipment, training and material, the desired effectiveness of the practice will be difficult to achieve. Foaming a runway can also result in the airport fire department being short of agent at a critical time, if the firefighters are involved in fire suppression after the landing.