The Evergreen Supertanker is a Boeing 747-200, modified by Evergreen International Aviation into a 24,000 US gallon (94,850 litre) capacity aerial firefighting aircraft. This is double the capacity of the next largest air tanker in operation, the Tanker 910. The Evergreen Supertanker was scheduled to be available to fight fires from summer 2008 but has not yet entered service.
Unique technology is used on the Evergreen Supertanker in order to allow an aircraft as large as a 747 to carry out aerial fire fighting.
Current fire fighting aircraft use a gravity drop system. Doors in the underside of the aircraft open, allowing the contents of the tanks to discharge. This type of system requires an aircraft to fly very low, typically 200ft above ground level. The Evergreen Supertanker has a pressurised system. This can disperse retardant under high pressure, for an overwhelming response, or drop retardant equivalent to the speed of falling rain. This system allows the aircraft to operate within its design criteria.
Using the pressurised system, the aircraft can deliver retardant to the scene of a fire whilst flying at a height of 400 to 800ft, at approximately 140kts (160mph) (260kph), configured as if it were on approach for landing.
The Evergreen Supertanker’s tank system can be configured for segmented drops, allowing the contents of the tank to be released at multiple intervals while in flight.