Air Tankers
Various airplanes of differing size and function are used to aid in wildfire suppression efforts. In the past, World War II-era bombers were the mainstay of the aerial fleet. In the present day, however, newer, purpose-built air-tankers are being brought into service.
Air-tankers have the capacity to drop large amounts of water and/or fire retardant— the largest (an IL-76 air-tanker) has the capacity to carry 15,000 gallons of water/retardant, and there are plans to develop a Boeing 747 aerial fire-fighter (which could carry up to 24,000 gallons).
photo by spotfireimages
The smallest aircraft used in fire suppression drops are Single Engine Air Tankers, or SEATs. These are agricultural sprayers that can drop about 800 gallons of water or fire retardant. Smaller air-planes often serve as lead planes or spotters. Spotter planes can be found at high altitudes, coordinating suppression efforts of the larger air-tankers. Lead planes fly ahead of air-tankers (which must drop their loads of retardant/water bomber-style),marking the trajectory for the wildfire assault.
Water loads are often dropped directly on wildfire flames (the effects of water are rather short-lived). Retardant drops, however, can be made ahead of flame fronts or along their edges, creating an artificial firebreak. This is especially useful in areas too rugged or remote for ground crews to access.
In the past, retardants were comprised of borate salts. Nowadays, newer, more environmentally-friendly retardants are utilized in fire suppression. Ammonium sulfate and ammonium polyphosphate-based retardants actually act as fertilizers for the new growth of plants. These retardants can be harmful to fish if dropped in water sources, however.