84. The following authorities shall have power to convene a field general court martial, namely:-(a) an officer empowered in this behalf by an order of the Government or of the Chief of Army Staff;(b) on active service, an officer commanding a portion of the Bangladesh Army, not below the rank of ¹[Brigadier General], if in the opinion of such officer commanding, such opinion to be recorded in writing and to be conclusive, it is not practicable with due regard to discipline and the exigencies of the service to try the alleged offender by a general court martial.