DOD memo CJCSI 3610.01A June, 2001 AIRCRAFT PIRACY (HIJACKING) AND DESTRUCTION OF DERELICT AIRBORNE OBJECTS http://www.dtic.mil/doctrine/jel/cjcsd/cjcsi/3610_01a.pdf
4. Policy.
a. Aircraft Piracy (Hijacking) of Civil and Military Aircraft. Pursuant to references a and b, the Administrator, Federal Aviation Administration (FAA), has exclusive responsibility to direct law enforcement activity related to actual or attempted aircraft piracy (hijacking) in the “special aircraft jurisdiction” of the United States. When requested by the Administrator, Department of Defense will provide assistance to these law enforcement efforts. Pursuant to reference c, the NMCC is the focal point within Department of Defense for providing assistance. In the event of a hijacking, the NMCC will be notified by the most expeditious means by the FAA.
The NMCC will, with the exception of immediate responses as authorized by reference d, forward requests for DOD assistance to the Secretary of Defense for approval. DOD assistance to the FAA will be provided in accordance with reference d. Additional guidance is provided in Enclosure A.
DoD Directive 3025.15, "Military Assistance to Civil Authorities", February 18, 1997 ("Reference D" from DOD directive DOD memo CJCSI 3610.01A June, 2001)
http://www.dtic.mil/whs/directives/corres/pdf/302515p.pdf
Nothing in this Directive prevents a commander from exercising his or her immediate emergency response authority as outlined in DoD Directive 3025.1 (reference (g))
4.5. With the exception of immediate responses under imminently serious conditions, as provided in subparagraph 4.7.1., below, any support that requires the deployment of forces or equipment assigned to a Combatant Command by Secretary of Defense Memorandum (reference (j)), must be coordinated with the Chairman of the Joint Chiefs of Staff.
4.7. Requests for military assistance should be made and approved in the following
ways:
4.7.1. Immediate Response. Requests for an immediate response (i.e., any form of immediate action taken by a DoD Component or military commander to save lives, prevent human suffering, or mitigate great property damage under imminently serious conditions) may be made to any Component or Command. The DoD Components that receive verbal requests from civil authorities for support in an exigent emergency may initiate informal planning and, if required, immediately respond as authorized in DoD Directive 3025.1 (reference (g)). Civil authorities shall be informed that verbal requests for support in an emergency must be followed by a written request. As soon as practical, the DoD Component or Command rendering assistance shall report the fact of the request, the nature of the response, and any other pertinent information through the chain of command to the DoD Executive Secretary, who shall notify the Secretary of Defense, the Chairman of the Joint Chiefs of Staff, and any other appropriate officials. If the report does not include a copy of the civil authorities' written request, that request shall be forwarded to the DoD Executive Secretary as soon as it is available.
DOD Directive 3025.1 Military Support to Civil Authorities (MSCA) (Reference G" from DoD Directive 3025.15)
http://www.dtic.mil/whs/directives/corres/pdf/302501p.pdf
4.5. Immediate Response
4.5.1. Imminently serious conditions resulting from any civil emergency or attack may require immediate action by military commanders, or by responsible officials of other DoD Agencies, to save lives, prevent human suffering, or mitigate great property damage. When such conditions exist and time does not permit prior approval from higher headquarters, local military commanders and responsible officials of other DoD Components are authorized by this Directive, subject to any supplemental direction that may be provided by their DoD Component, to take necessary action to respond to requests of civil authorities. All such necessary action is referred to in this Directive as "Immediate Response."
4.9. Emergency Priorities. When guidance cannot be obtained from higher headquarters on a timely basis, due to attack on the United States or other emergency circumstances, the DoD Components should apply DoD resources to MSCA in the following order of priority:
4.9.1. To save human life and mitigate human suffering, and to protect essential U.S. Government capabilities, including:
4.9.1.1. Continuity of the U.S. Government.
4.9.1.2. Protection of U.S. Government officials.
4.9.1.3. Prevention of loss or destruction to Federal property.
4.9.1.4. Restoration of essential Federal functions.
4.9.2. To preserve or restore services of State and local government.
E2.1.18. Immediate Response. Any form of immediate action taken by a DoD Component or military commander, under the authority of this Directive and any supplemental guidance prescribed by the Head of a DoD Component, to assist civil authorities or the public to save lives, prevent human suffering, or mitigate great property damage under imminently serious conditions occurring where there has not been any declaration of major disaster or emergency by the President or attack.
E2.1.19. Imminently Serious Conditions. Emergency conditions in which, in the judgment of the military commander or responsible DoD official, immediate and possibly serious danger threatens the public and prompt action is needed to save lives, prevent human suffering, or mitigate great property damage. Under these conditions, timely prior approval from higher headquarters may not be possible before action is necessary for effective response.