Definition

Military/Civil Coordination in aviation covers issues such as clearance of military formation flights, military air traffic controllers assisting with civil aircraft in certain airspace, and monitoring of restricted and prohibited airspace. Other coordination matters include joint use airports, military flight routing during contingencies, and airspace security.

Military Formation Flights

Military formation flights routinely transit civilian-controlled airspace. Additionally, military aircraft on cross-country flights sometimes land and depart from civilian airports. These situations require civilian controllers to be familiar with certain military procedures. 

While flying en route in standard formation, the lead aircraft normally transmits, or "squawks," a discrete transponder code. Other aircraft in the formation will keep their transponders on standby mode. This prevents signal garbling and false Traffic Collision Avoidance System (TCAS) indications.

In a standard formation, according to International Civil Aviation Organisation (ICAO) procedures, the distance between aircraft should not exceed 0.5 NM horizontally and 100 ft vertically. Some countries extend these limits. For example, in the U.S., a formation is considered standard if the horizontal spacing is within one NM. Standard formations are treated as a single aircraft with regard to navigation and position reporting.

Some operations, such as aerial refueling flights, require nonstandard formations. These formations, sometimes called "cell formations," allow for greater spacing between aircraft. This becomes necessary when, for example, multiple aircraft in a refueling operation need to maneuver into contact position behind the tanker aircraft. This may require an altitude reservation (ALTRV) and special handling.

Arrival and departure procedures for formation aircraft can vary. In some countries, formation departures and arrivals are not permitted at civilian airports. Where permitted, departures usually involve takeoff at specified intervals, such as one minute or less between aircraft. Arrivals can involve tactical procedures such as overhead breaks. In such arrivals, aircraft overfly the field at a specified altitude, then bank steeply for interval landings. These tactical procedures are designed to minimize exposure to hostile fire.

Aircraft transiting to combat zones may overfly friendly civilian airspace on an instrument flight rules (IFR) flight plan, then cancel IFR and fly under visual flight rules (VFR) as they near the combat entry point. Exiting a combat zone, they may reverse the procedure and call for an IFR clearance on the return flight.

Military Authority Assumes Responsibility for Separation of Aircraft (MARSA)

When flying in civilian-controlled airspace, military flights may in some situations declare MARSA, for Military Assumes Responsibility for Separation of Aircraft. This temporarily delegates separation responsibility to the military authority operating the flights, thereby relieving Air Traffic Control (ATC) of workload.

The procedure means the civilian controller does not have to provide separation between participating military aircraft. Civilian ATC still handles separation between the military formation and civil aircraft. MARSA is initiated only by military aircraft (and this can include civilian-owned aircraft under contract to the military).

Typically, an aircraft commander will declare MARSA for only a portion of a flight. For example, when military aircraft approach a rendezvous point for a low-level formation exercise, MARSA may be used only for the duration of the low-level training. 

Military Air Traffic Control of Civilian Aircraft

In many cases, civilian aircraft transit airspace handled by military controllers. For example, in the busy airspace of the mid-Atlantic region of the United States, approach controllers at Joint Base Andrews near Washington, DC, work as part of the larger Potomac Terminal Radar Approach Control (TRACON). A civilian Air Route Traffic Control Center (ARTCC) may hand off a civilian flight to a military controller (or vice versa) in seamless fashion. Large military air bases around the world use this arrangement to coordinate air traffic with civilian authorities.

Civil aircraft in distress can declare an emergency and land at military airfields in most countries, if no safer options exist. Military airfields may have more robust Rescue and Firefighting Services (RFFS) than small civilian airports. However, unexpected civilian aircraft present a security risk for military bases, and civilian use of military fields is considered a last resort.

In most countries, military aircraft typically operate with ultra high frequency (UHF) radios, and civil aircraft use very high frequency (VHF) radios. This requires military controllers to transmit and receive in duplex mode to avoid communication problems. Similarly, civilian controllers can communicate in duplex mode with military aircraft.

Joint Use Airports

A number of military air bases around the world share facilities with civilian operators. For example, in Honolulu, Hawaii, in the U.S., Joint Base Pearl Harbor Hickam (the former Hickam Air Force Base), shares runways with Daniel K. Inouye International Airport. Similar arrangements exist at Baghdad International Airport in Iraq, Naha Airport in Japan, and many others around the world. 

Joint use airports are normally configured so that the civilian terminals and other facilities occupy one side of the airport property, and the military base occupies space on the other side of the runway complex. Civilians have the usual access on the civilian side, and the military maintains restricted access on the other. Certain taxiways that lead to the military ramp are closed to civilian traffic. Military police enforce these taxiway and ramp restrictions. Signage may carry warnings such as: MILITARY TRAFFIC ONLY. USE OF DEADLY FORCE AUTHORIZED.

Air traffic controllers at joint use airports can be military or civilian, or a combination of both.

Management of Special Use Airspace

Certain airspace around the world is prohibited for all civilian aircraft. Such airspace is known as Prohibited Areas. Controllers monitor these areas for violations, and when appropriate, warn aircraft nearing the areas and alert military authorities. Other airspace, such as Restricted Areas, may be transited by civilian aircraft when not in use for military purposes. Military and civilian air traffic controllers and other authorities coordinate times for activation and deactivation of Restricted Areas. This protects civilian aircraft from areas where military aircraft may be conducting weapons training, low-level flight, and other potentially hazardous operations. 

Planned flights for civilian aircraft may cross Restricted Areas as long as the crossing takes place when the area is inactive. Pilots and controllers often refer to active Restricted Areas as "hot," and inactive Restricted Areas as "cold." Civilian aircraft entering a hot Restricted Area are warned by controllers and usually given a heading for departing the area. Violating a Prohibited Area or a hot Restricted Area can involve penalties by the relevant Air Navigation Service Provider (ANSP).

Another important area of coordination is the use of Air Defense Identification Zones (ADIZ). An ADIZ is an area of airspace over land or water, usually extending out from a national border, in which the ready identification, location, and control of aircraft is required in the interest of national security. Entering an ADIZ normally requires an approved and activated flight plan. Most countries also require certain equipment for ADIZ penetration, such as a transponder and two-way radio. Flights entering an ADIZ without meeting these requirements may be intercepted by military aircraft. 

Airspace Security

In extreme situations, military and civilian air traffic controllers and other authorities can coordinate restriction or complete shutdown of civil air traffic. Such an event took place in the U.S. following the terrorist attacks of Sept. 11, 2001. This involved the activation of what was then called Security Control of Air Traffic and Air Navigation Aids (SCATANA).

According to the National Air Traffic Controllers Association (NATCA), when an order went out to land every civilian aircraft at the nearest airport, controllers guided 700 aircraft to land in the first four minutes, 2,800 in the first hour, and more than 4,500 within the first three hours. Civilian air traffic in the U.S. remained grounded for two days.

A similar program now exists under the name Emergency Security Control of Air Traffic (ESCAT), described in the U.S. Code of Federal Regulations 32 CFR 245 and the U.S. Federal Aviation Administration's (FAA) Advisory Circular (AC) 99-1E. The AC defines ESCAT as "an emergency preparedness plan that prescribes the joint action to be taken by appropriate elements of [the Department of Defense], the Department of Transportation, and the [Department of Homeland Security] in the interests of national security to control air traffic under emergency conditions."

Other countries have similar programs. 

Intercept Procedures

Civilian pilots are expected to know procedures to follow in case of intercept by military aircraft. Intercept could happen for any number of reasons, including navigation error or sudden and unexpected shutdown of airspace due to a contingency. Procedures are established by State regulators, and they are fairly standard from country to country. More detail can be found in  Military Interception Signalling. Signalling methods include rocking wings and flashing navigation lights to communicate acknowledgement of the interception.

All pilots are urged to monitor emergency frequencies 121.5 VHF and/or 243.0 UHF to help avoid intercept situations. These frequencies are sometimes referred to as the "guard" frequencies. An intercepted aircraft, or an aircraft about to penetrate special use airspace or an ADIZ without clearance, may be addressed as "Unknown Rider." Controllers or intercepting military pilots may also refer to such aircraft simply as "Aircraft squawking (transponder number) at (altitude) and (heading)."