The 747 Supertanker (Evergreen)

The Evergreen Supertanker is a Boeing 747-100 widebody aircraft that was modified into an aerial firefighting aircraft by Evergreen International Aviation. The aircraft was originally manufactured by Boeing in 1971 for Delta Air Lines.[1] With a capacity of 20,500 US gallons (77, 600 liters), it is the largest aerial firefighting aircraft in the world.[2] The next largest firefighting tanker aircraft is the Ilyushin Il-76P. The Supertanker entered service for the first time in 2009, fighting a fire in Cuenca, Spain.[3] The tanker made its first American operation on 31 August 2009 at the Oak Glen Fire.[4][5] The current tanker is N479EV, tanker/tail number 979. (The previous plane was: N470EV, tanker/tail number 947.) Development Development started after the 2002 fire season, which saw the fatal crashes of two air tankers in the USA. The accidents, involving a Lockheed C-130A Hercules and a Consolidated PB4Y-2, prompted the U.S. Department of Interior to issue an official Request for Information on next-generation airtankers.[6] Evergreen proposed to convert up to four of its Boeing 747-200 Freighters into massive 'Supertankers'. The first converted Boeing 747 (N470EV) made its maiden flight on February 19, 2004.[6] The current Supertanker is N479EV, a 747-100. By June 2006, Evergreen had spent $40 million on the project and was hopeful of both FAA certification, and an evaluation contract from the US Forest Service.[7] In October 2006 the FAA issued Evergreen a supplementary type certificate for the installation and removal of internal tanks, associated systems and support structure for the aerial dispersant of liquids.[8] An issue that impacted usage by the Forest Service was the USFS requirement for using fire retardant rather than water. When Evergreen attempted to convert the system from water dispensing to retardant, they encountered objections from the FAA. The FAA's issue related to the much greater density of fire retardant and the corresponding increased stress on the airframe thus delaying the FAA certification. The FAA determined that the Supertanker's service life would be diminished and also raised concerns about the dangers of additional stress on the airframe during firefighting operations and heavy weight maneuvering. From Wikipedia