The Philippine Air Force has grounded its 11 remaining FA-50 jets after one of its fighter aircraft crashed in the southern province of Bukidnon on Tuesday, resulting in the deaths of two pilots.

An investigation has been launched to find the cause of the crash, as the fighter jets are vital to the military’s air defense, local Cebu Daily News reported on Thursday.

The military confirmed Wednesday that both pilots were found dead on Wednesday near the wreckage of the missing South Korea-made fighter jet near Mount Kalatungan in Bukidnon.

The fighter jet went missing on Tuesday during a tactical night operation as ground troops engaged in clashes with members of the New People's Army, a Maoist armed group, in Bukidnon.