Nowshera, May 17 (ANI): Two trainer aircraft of Pakistan Air Force (PAF), on a routine training mission in northwest of Islamabad, collided mid air and crashed today killing all four pilots on board, and injuring at least five persons on the ground. The two planes had taken off from an air base in Resalpur and crashed shortly after take off into a civilian area near Nowshera close to the air base. Residents said that the aircraft burst into flames after hitting the roofs of two houses.