World's Biggest Aircraft - The Antonov An-225 Mriya

The Antonov An-225 Mriya (Ukrainian: Антонов Ан-225 Мрія, Dream, NATO reporting name: 'Cossack') is a strategic airlift cargo aircraft, designed by the Soviet Union's Antonov Design Bureau in the 1980s. The An-225's name, Mriya (Мрiя) means "Dream" (Inspiration) in Ukrainian. It is generally acknowledged as the largest airplane in the world; it is the heaviest aircraft with a gross weight of 640 tonnes and the biggest heavier-than-air aircraft in terms of length and wingspan in operational service.
The An-225, originally developed specifically to transport the Buran orbiter, was an enlargement of the successful Antonov An-124. The first An-225 was completed in 1988 and a second An-225 has been partially completed. The completed An-225 is in commercial operation with Antonov Airlines carrying oversized payloads. Among its many records, it holds the absolute world record for airlifted payload at 189,980 kilograms (418,834 pounds).

Development
The Antonov An-225 was designed to airlift the Energia rocket's boosters and the Buran space shuttle for the Soviet space program. It was developed as a replacement for the Myasishchev VM-T. The An-225's original mission and objectives are almost identical to that of the United States' Shuttle Carrier Aircraft.
An-225 with Buran atop lands at the Paris Air Show in 1989.
The An-225 first flew on 21 December 1988 with a 74 minute flight from Kiev. The aircraft was on static display at the Paris Air Show in 1989 and it flew during the public days at the Farnborough air show in 1990. Two aircraft were ordered, but only one An-225 (registration CCCP-82060 later UR-82060[6]) was finished. It can carry ultra-heavy and oversize freight, up to 250,000 kg (550,000 lb) internally, or 200,000 kg (440,000 lb) on the upper fuselage. Cargo on the upper fuselage can be 70 metres (230 ft) long.
A second An-225 was partially built during the late 1980s for the Soviet space program. The second An-225 included a rear cargo door and a redesigned tail with a single vertical stabilizer. It was planned to be more effective for cargo transportation. Following the collapse of the Soviet Union in 1991 and the cancellation of the Buran space program, the lone operational An-225 was placed in storage in 1994. The six Ivchenko Progress engines were removed for use on An-124s, and the second uncompleted An-225 airframe was also stored. The first An-225 was later re-engined and put into service.
By 2000, the need for additional An-225 capacity had become apparent, so the decision was made in September 2006 to complete the second An-225. The second airframe was scheduled for completion around 2008, then delayed. By August 2009, the aircraft had not been completed and work had been abandoned In May 2011 Antonov CEO is reported to have said that the completion of a second An-225 Mriya transport aircraft with a carrying capacity of 250 tons requires at least $300 million, but if the financing is provided, its completion could be achieved in three years. According to different sources, the second An-225 Mriya is 60–70% complete.