Chinese Panda Yang Guang arrives at Edinburgh Airport on December 4, 2011 in Edinburgh, Scotland. Tian Tian and Yang Guang, a pair of eight-year-old giant pandas arrived on a specially chartered flight and will be the first to live in the UK for 17 years. Edinburgh Zoo are hopeful that the pandas will give birth to cubs during their 10 year stay in Scotland. (Photo by Jeff J Mitchell/Getty Images)

Željava Air Base, situated on the border between Croatia and Bosnia and Herzegovina under Plješevica Mountain, near the city of Bihać, Bosnia, was the largest underground airport and military air base in the former Yugoslavia, and one of the largest in Europe. (Photo by Thomas Windisch/Exclusivepix Media)

Mount Agung's eruption is seen next to a Balinese temple at Kubu sub-district in Karangasem Regency on Indonesia's resort island of Bali on November 26, 2017. Indonesia authorities raised the alert for the rumbling volcano to highest level on Monday and closed the international airport on tourist island of Bali stranding thousands of travelers. (Photo by Sonny Tumbelaka/AFP Photo)

A worker looks on with his camel as he waits for tourists at the Giza Pyramids on the outskirts of Cairo, Egypt, November 8, 2015. Egypt's Tourism Minister Hesham Zaazou said Cairo regretted the suspension of flights and was doing all it could to secure its airports and tourist sites, adding that he would fly to Sharm al-Sheikh to oversee measures to support tourists there. (Photo by Amr Abdallah Dalsh/Reuters)

An injured supporter of Kenyan opposition leader Raila Odinga receives assistance in Nairobi, Kenya on November 17, 2017. Kenyan police have used tear gas and water cannons to disperse supporters of opposition leader Raila Odinga who are trying to gather near the country's main airport and Uhuru park to welcome him back from an overseas trip. (Photo by Baz Ratner/Reuters)

A soldier from the African Union (AU) peacekeeping force stands guard at the site where a cargo plane carrying supplies for AU troops crash-landed outside Somalia's capital, on October 13, 2015 at Abirska, some 18 kilometres outside Somalian capital, Mogadishu. The officials said the Egyptian-owned transport plane went down after making several unsuccessful passes over the seafront airport. Two of the six crew members suffered light injuries in the crash, the officials said, but added that the plane and those on board were safe having landed in an area controlled by the Somali government and the African Union's AMISOM force. (Photo by Mohamed Abdiwahab/AFP Photo)

Photographers gather to take pictures of pilot Andre Borschberg (C) ahead of the take off of Solar Impulse 2-a solar powered plane- in Nanjing, China, May 31, 2015. The world's largest solar-powered airplane, Solar Impulse 2, took off from eastern China's Nanjing on Sunday to continue its round-the-world voyage. The Swiss-made plane left Nanjing's Lukou International Airport at 2:39 in the early morning, with former fighter pilot Borschberg at the controls alone for the entire 8,200-kilometer flight from Nanjing to Hawaii, the toughest leg of its marathon adventure. (Photo by Reuters/Solar Impulse)