Helicopters are seen in the China Helicopter Expo 2019 held from Oct. 10 to 13 at the China Tianjin Port Free Trade Zone. [Photo/VCG]

A helicopter is seen in the China Helicopter Expo 2019 held from Oct. 10 to 13 at the China Tianjin Port Free Trade Zone. [Photo/VCG]

Helicopters are seen in the China Helicopter Expo 2019 held from Oct. 10 to 13 at the China Tianjin Port Free Trade Zone. [Photo/VCG]

Helicopters are seen in the China Helicopter Expo 2019 held from Oct. 10 to 13 at the China Tianjin Port Free Trade Zone. [Photo/VCG]

A helicopter is seen in the China Helicopter Expo 2019 held from Oct. 10 to 13 at the China Tianjin Port Free Trade Zone. [Photo/VCG]