A biplane taking part in the Vintage Air Rally lands, in Stellenbosch, near Cape Town, South Africa December 16, 2016. (Photo by Mike Hutchings/Reuters)

A Hot air balloon is seen at the Cup Hot Air event during the Air Sports festival titled “70 Years of Peaceful Sky” in Minsk, Belarus July 18, 2015. (Photo by Vasily Fedosenko/Reuters)

Spanish Patrulla Aguila (C-101), aerobatic demonstration team of the Spanish Air Force performs during the Radom Air Show at an airport in Radom, Poland August 23, 2015. (Photo by Kacper Pempel/Reuters)

The Screamin' Sasquatch jet powered Waco Biplane sits on display during media day for the Canadian International Air Show at Billy Bishop Airport, Toronto, Ontario, September 4, 2015. (Photo by Louis Nastro/Reuters)

A Russian air force technician reports to a pilot that a bomber is ready for a combat mission at Hemeimeem air base in Syria Wednesday January 20, 2016. Russian warplanes have flown over 5,700 combat missions since Moscow launched its air campaign in Syria on September 30, 2015. (Photo by Vladimir Isachenkov/AP Photo)

An injured girl reacts at a site hit by an airstrike in the rebel-held Douma neighbourhood of Damascus, Syria November 7, 2016. (Photo by Bassam Khabieh/Reuters)

People leave a giant air purifier, which its inventor calls a “super tree”, in Lima's district of Jesus Maria November 24, 2014. In Peru's notoriously polluted capital Lima, local inventor Jorge Gutierrez, a retired naval engineer, is deploying the giant air purifiers that double as billboards to suck up carbon dioxide and dangerous levels of smog. (Photo by Mariana Bazo/Reuters)

A grizzly bear eats a frozen fruits during a hot summer day at Rio de Janeiro's zoo January 13, 2015. According to a local climate institute, temperatures in Rio de Janeiro on Tuesday rose up to 34 degrees Celsius (93.2 degrees Fahrenheit). (Photo by Sergio Moraes/Reuters)