Related Rule
Practice Relating to Rule 17. Choice of Means and Methods of Warfare
The Joint Circular on Adherence to IHL and Human Rights (1991) of the Philippines states:
The use of aerial/naval and artillery/mortar fires for interdiction and harassment especially when the fire missions are unobserved and near populated areas and when civilian casualties/material damages are likely to be incurred is strictly prohibited … Air strikes may be used under judicious circumstances. Targets shall be carefully evaluated by the close air support commander for approval by the Area Commander. During an actual engagement where the security of an AFP/PNP unit or critical installation/facility is threatened and time is of the essence, the commander of the engaged unit, on his own authority, may selectively apply available fire support means to defend his unit or position, however exercising utmost care to prevent or minimize civilian casualties/material damage. 
Philippines, Implementation Guidelines for Presidential Memorandum Order No. 393, dated 9 September 1991, Directing the Armed Forces of the Philippines and the Philippines National Police to Reaffirm their Adherence to the Principles of Humanitarian Law and Human Rights in the Conduct of Security/Police Operations, Joint Circular Number 2-91, Department of National Defense, Department of Interior and Local Government, 1991, § 2(c).