By Hyonhee Shin SEOUL (Reuters) -Two South Korean air force planes collided in mid-air on Friday during a training exercise, killing four pilots, authorities said. A total of 130 troops, 95 police officers and 60 firefighters as well as three helicopters have begun a search at the crash site, the Yonhap news agency said, citing local government officials. The crash happened about 6 km (3.7 miles) south of the KT-1 airplane base in the southeastern city of Sacheon, at about 1:37 p.m.(0437 GMT), the air force said. “Despite their attempts at an emergency escape … all of the two student pilots …