A Russian ground staff member signals to the pilot of a Sukhoi Su-25 fighter jet at the Hmeymim air base near Latakia, Syria, in this handout photograph released by Russia's Defence Ministry October 22, 2015. (Photo by Reuters/Ministry of Defence of the Russian Federation)

North Korean leader Kim Jong Un smiles as he attends a flight training session by female fighter pilots Jo Kum Hyang and Rim Sol in this undated photo released by North Korea's Korean Central News Agency (KCNA) on June 22, 2015. (Photo by Reuters/KCNA/Antara Foto)

A Syria Democratic Forces (SDF) fighter comforts a civilian who was evacuated with others by the SDF from an Islamic State-controlled neighbourhood of Manbij, in Aleppo Governorate, Syria, August 12, 2016. The SDF has said Islamic State was using civilians as human shields. (Photo by Rodi Said/Reuters)

Participants pass an egg using their mouths during a religious ritual as they play the role of traditional fighters in a parade during the Popo (Mask) Carnival of Bonoua, in the east of Abidjan, April 18, 2015. The carnival has its origins in the changes that Aboure youths in Bonoua introduced to the annual festival of yams. (Photo by Luc Gnago/Reuters)

A U.S. Army B-24 Liberator Bomber is hailed by a ground crewman as it takes off over a line of shark- nosed fighter planes at an advanced base in China on a mission on October 10, 1943, to bomb Japanese installations. (Photo by AP Photo)

Tajammu Al-Ezza brigade fighters react while firing a Grad shell towards forces of Syria's President Bashar Al-Assad stationed in Salhab village, Hama countryside, May 7, 2015. (Photo by Mohamad Bayoush/Reuters)

A French Air Force Mirage 2000 fighter jet takes off during the close air support (CAS) exercise Serpentex 2016 hosted by France in the Mediterranean island of Corsica, at Solenzara air base, March 17, 2016. Serpentex is an annual exercise that involves joint terminal attack controllers (JTACs) from 12 countries from March 7 to March 25, 2016. (Photo by Charles Platiau/Reuters)