Supporting arms synchronization of fires: altitude separation of FA and fixed-wing CAS.

Joint fire support manuals provide guidance for altitude separation of FA and fixed-wing aircraft yet fail to present detailed instructions to fire supporters in calculating the "stay aboves" and "stay belows." This article shows the calculations that allow fixed-wing aircraft to fly closer to the artillery trajectory rather than having to use maximum ordinate (MAXORD) during the ordnance delivery portion of the flight profile.

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Suppression of Enemy Air Defenses (SEAD). The SEAD mission may be used when friendly aircraft can't complete their mission without critically exposing themselves to a ground threat, such as air defense artillery (ADA). (Throughout this article, any ground threat to friendly aircraft will be referred to as "ADA.") Indirect fires suppress the ADA via SEAD missions and mark the target (threat to ground forces) for the aircraft to attack. If ADA is suppressed, it's less likely to acquire and engage the aircraft.

There are two types of SEAD missions: standard, and non-standard.

There are two types of standard SEAD missions: continuous and interrupted. The continuous timeline has rounds impacting at -1, -:30, 0, +:30 and +1 minutes. The mark is at -:30 for white phosphorous (WP)/red phosphorous (RP) or -:45 for illumination on the deck (IOD). The interrupted timeline has rounds impacting at -1 and -:30. The mark is at -:30 for WP/RP or -:45 for IOD.

The non-standard timeline can include any coordinated and deconflicted supporting arms, as long as they are tailored to support the ground scheme of maneuver, suppress the ADA and mark the attack target.

Marks can be provided by indirect fire, direct fire or by laser. Laser marks (i.e., infrared pointers) and direct fire should be initiated 30 seconds before the close air support (CAS) time-on-target (TOT) and continued until 30 seconds after the CAS TOT. This provides Dash-2 (second aircraft of the two-ship section) the same redundant marks to orient onto if Dash-1 does not release its ordnance (Dash-2 usually orients off Dash-1's effects).

Types of Separation. Aircraft and SEAD fires may be separated by distance or time. This is commonly subdivided into lateral, time and altitude separation or any combination of these.

Lateral separation is effective for synchronizing indirect fire and aviation attacks against two adjacent targets. A specific distance separates the suppression fires from the targets aircraft are attacking. The minimum separation distance between suppression targets and aviation attack targets varies and should be based on the caliber of indirect fire fired at the suppression target. Based on the fixed-wing aircraft's ordnance, the pilot determines how far to stay above the fragmentation pattern.

Each unit must develop a minimum lateral separation for friendly units used in conjunction with indirect fires. A recommended minimum is 1,000 meters for artillery (155-mm) and 400 meters for mortars (81-mm). Units are not recommended to pass underneath active mortar gun-target lines (GTLs).

Establishing a temporary, informal air-space coordination area (ACA) is one method of maintaining lateral separation. For example, such an ACA could be, "Stay east of the Euphrates River."

If fixed-wing aircraft are attacking a target below 2,000 feet above ground level (AGL) in conjunction with artillery or mortars, the same lateral separation restrictions should apply. This is based on the vertical portion of the fragmentation pattern of indirect fires (155-mm) plus a 1,000-foot safety buffer.

Time separation may be required when aircraft can't be routed away from indirect fire trajectories or suppressed targets or must use extremely low ingress and egress flight profiles. This technique requires SEAD fires to be coordinated with the routing of aircraft so that although aircraft and SEAD fires occupy the same space, they don't do so at the same time.

Time separation should be used with mortar fires suppressing a fixed-wing aircraft target. It allows suppression before and after the CAS attack while not forcing the aircraft to stay above the mortar trajectory.

Mortar trajectories can be as high as 10,000 feet AGL. At this altitude, fixed-wing aircraft may have difficulties acquiring the mark or target and the forward air controller (FAC) may have difficulty acquiring the aircraft.

The SEAD interrupted mission is a good use of time separation while synchronizing mortars and fixed-wing aircraft against the same target. If suppression is desired after the aircraft attack, a separation of two minutes from the CAS TOT allows Dash-2 to clear the area before mortars fire again. This is based on the mortars' average time-of-flight (TOF) and an additional 15-second safety factor in case Dash-2 is late or mortars fire early.

A separation of one minute and 30 seconds from the CAS TOT is recommended for artillery (based on a smaller average TOF). Using time separation for artillery is not recommended and will not be necessary when using altitude separation.

Altitude separation is effective when aircraft can safely remain above or below indirect-fire trajectories and above their effects. This technique supports low-altitude or high-altitude CAS attacks and is the least restrictive to both indirect fire agencies and fixed-wing aviation. It allows indirect fires to continuously suppress the target the aircraft is attacking.

Establishing a temporary and informal ACA is one method of maintaining altitude separation. For example an ACA might be, "Stay above 7,600 feet MSL [mean sea level]" or "Stay below 4,900 feet AGL and above 2,000 feet AGL."

Attack Geometry. This refers to three general geometric possibilities in combining fixed-wing aviation and indirect fires: attacking and suppressing the same target, attacking long and suppressing short, and attacking short and suppressing long.

When attacking and suppressing the same target, there is no lateral separation of the aircraft and fires. Therefore, another separation plan must be used (see Figure 1).

The recommended technique for artillery is to suppress and mark the target while using altitude separation (i.e., stay above 2,000 feet AGL). The altitude separation should not be excessive in terms of the pilot's ability to acquire the target visually or the FAC's ability to acquire the aircraft. This allows a large caliber weapon to continually suppress the ADA during the fixed-wing attack.

The recommended technique for mortars is to suppress and mark the target while using time separation for the suppression. Due to the mortar's high trajectory, it is not recommended to continuously suppress a target while attacking it with fixed-wing aviation. This would require the aircraft to stay above the mortar trajectory. Instead, use time separation (i.e., the SEAD interrupted mission).

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If using direct fire as a redundant mark, the aircraft should stay above its potential ricochets and effects. Recommendations for altitude separation using direct fire is 5,000 feet AGL for tank main gun and 25-mm gun fires, 4,000 feet AGL for .50-caliber machine guns and 3,000 feet AGL for 7.62-mm or 5.56-mm fires.

When attacking long and suppressing short, the ADA threat is separated from the attack target and is closer to the firing agencies. Therefore, use several separation plans (see Figure 2).

The recommended technique for artillery when suppressing short is to continuously suppress the ADA target and mark the attack target. Lateral separation is used for the ADA target (it should be more than 1,000 meters from the attack target). Time separation for the marking round on the attack target should be used. The aircraft's route should not cross the active suppression GTL.

The preferred technique for mortars is to suppress and mark the attack target if artillery or a better agency is available to suppress the ADA. Because of the mortar's high trajectory, don't continuously suppress a target while attacking it with fixed-wing aviation. Instead, use time separation.

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When attacking short and suppressing long, the ADA is separate from the attack target and at a greater distance to the firing agencies. Therefore, use several separation plans (see Figure 3).

The preferred technique for artillery is to suppress the ADA target continuously and mark the attack target. There is no lateral separation from the ADA target because the aircraft is crossing the active suppression GTL. There is no time separation on the attack target because of continuous suppression GTL on the ADA threat. Therefore, use altitude separation.

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The preferred technique for mortars is to suppress and mark the attack target. Because of the mortar's high trajectory, don't continuously suppress a target while attacking it with fixed-wing aviation. Instead, use time separation.

Fixed-Wing Aircraft Attack Profiles. The enemy threat, weather conditions, type of ordnance, type of suppression, FAC's ability to acquire the aircraft and the pilot's ability to acquire the target all factor into which flight profile the aircraft will fly. The attack profile affects the attack geometry and thus the type of separation needed.

The pilot should have a final attack "cone" of between 15 and 30 degrees wide. The cone should be separated radially from an active GTL and measured in degrees and have the attack target as the common center. During ingress, the pilot should be given egress instructions not to cross active GTLs, and the cone should be separated radially from the GTL by 30-degrees to keep the aircraft from inadvertently crossing the GTL while maneuvering for a fire solution. The aircraft has a higher risk of crossing the active GTL with fewer degrees of separation. At the same time, the higher the degree of separation, the more restrictive it is for the pilot.

The final attack cone may cross the active GTL on the descending branch, straddle the summit or cross the ascending branch only. If the final attack cone straddles the summit, use the maximum ordinate of the trajectory for altitude separation (+/- a safety factor). Based on the tactical positioning of artillery units in relation to the forward line of troops (FLOT), 99 percent of the altitude separation means will have the final attack cone crossing the descending branch. At this point, this article addresses this scenario only.

Calculating Altitude Separation. Before making the decision to use altitude separation, plot everything in the battlespace. This reveals the attack geometry and, thus, the separation needed for fixed-wing aircraft and artillery.

When providing altitude separation, be as precise as possible while plotting, measuring and calculating. Precise calculations guarantee the safety of the aircrew. The following steps show how to calculate altitude separation for a specific tactical scenario.

1. Gather the materials you need: artillery trajectory charts (in this case, Charge 6 White Bag: "CHG6WB, M107 HE"), a measuring ruler (Graphic Training Aid 06-05-001, called the "pizza cutter"), map pens, a Twentynine Palms East map, a round protractor, a calculator and an altitude deconfliction cheat sheet.

2. Plot a mechanized company at grid NU702064 (see Figure 4). Plot an artillery battery at grid NU724035. Plot an enemy mechanized company at grid NU702091; this is the attack target. Plot enemy ADA at grid NU657114; this is the suppression target.

3. Draw a line from the battery to the suppression target. This line is the active suppression GTL the aircraft will cross. Measure this range.

The range to target is 10,300 meters. The mission will be fired using Charge 6 White Bag.

Extract the suppression target altitude from the map. The target altitude is 880 meters. Convert that into feet by multiplying by 880 X 3.3. The target altitude is 2,900 feet.

4. Ask the FAC for the final attack cone and plot it on the attack target. Draw out both sides of the cone because it helps you visualize the potential ingress and egress routes in relation to geography, friendly and enemy units and the active GTL. If there are specific egress instructions, then draw them on the map.

For this scenario, the final attack cone is 045 to 090 degrees magnetic. When drawing the final attack cone, remember you must convert degrees magnetic to degrees grid--the grid to magnetic (GM) angle at Twentynine Palms is--240 mils.

To "declinate" the protractor, draw a permanent line on the protractor from 6160 mils to 2960 mils. This allows the protractor to orient on the map in degrees magnetic. Place two elastic "bowties" on the protractor and mark off the final attack cone.

Place the center of the protractor over the attack target and place pen marks on the map that represent both sides of the final attack cone. Draw the final attack cone by connecting the pen marks; ensure the cone intersects the GTL.

5. Measure the range from the battery to the point(s) of intersection between the final attack cone and the GTL. The ranges are 6,000 meters and 8,300 meters.

6. Locate the trajectory chart for Charge 6 White Bag and place a mark at range 10,300 meters along the 0 meter line. (See Figure 5.) If there is no trajectory that intersects this range, construct a trajectory by visually interpolating the distance between the next highest or lowest trajectory on the chart. Place pen marks along the 0 meter line at ranges 6,000 meters and 8,300 meters. Draw a straight-line perpendicular to the base of trajectory up toward the trajectory for 10,300 meters. Between where these lines intersect is where the aircraft will cross the GTL.

7. From these two intersections, draw a straight line from them to the left side of the trajectory chart until the line is perpendicular to the origin. Read (visually interpolate as necessary) the ordinate of each line. Extract the chart ordinates for these intersections. The ordinates are 1,400 meters for the higher line and 1,000 meters for the lower line.

8. Use the altitude deconfliction sheet to quickly calculate the chart ordinate times 3.3 +/- 1,000 meters for both stay aboves and stay belows (see Figure 6).

For stay aboves, multiply the higher chart ordinate times 3.3 and add a safety buffer; 1,000 feet is recommended. (This safety buffer assumes several risks in this calculation and will be discussed later.) As necessary, you express the stay-above number up to the next highest 100 feet listed on the altitude deconfliction cheat sheet. In this case, the results are 4620 expressed up to 4,700 feet + 1,000 feet = 5,700 feet. Add the target altitude: 5,700 feet + 2,900 feet = 8,600 feet at MSL, the final stay-above altitude.

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For stay belows, multiply the lower chart ordinate times 3.3 and subtract the safety buffer of 1,000 feet. As necessary, you express the number down to the next lowest 100 feet on the cheat sheet. In this case, the results are 3,300 feet - 1,000 feet = 2,300 feet (expressing the number down unnecessary). Add the target altitude: 2,300 feet + 2,900 feet = a final stay-below calculation of 5,200 feet MSL.

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9. Another fire supporter should verify the calculation. If the verifier calculates the stay above at a higher number, use it (it is safer). If the verifier calculates the stay below at a lower number, use it (it is safer). Ensure the FAC passes the stay-above and stay-below altitudes to the pilots.

Risks in Using a Rigid Trajectory. Using this method of altitude separation assumes three things. First, it assumes a rigid and parabolic artillery trajectory instead of a non-rigid and unpredictable trajectory. This allows a simple calculation using trajectory charts. Second, it assumes no inherent (systemic) errors that cause dispersion and that all conditions are standard. Third, it assumes the vertical interval (VI) between the firing unit and the suppression target is zero.

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These assumptions make for easy calculations, but they introduce a difference between the actual trajectory fired and the trajectory we use for the calculation (assumed trajectory). We can diminish the risks of this difference by factoring in a safety buffer. One thousand feet above and below the assumed trajectory is recommended as this safety buffer. The safety buffer of 1,000 meters is based on several factors. First, it is common sense to add a safety buffer. It is not an arbitrary number, such as 4,862.9 meters or 3,009 meters.

Second, adding 1,000 meters is easy, even when under combat stress, without a calculator, etc. Last, the 1,000-meter safety buffer (plus or minus) has a historical basis. It has been used through decades of combined-arms exercises (CAX) without incident.

Using exactly 1,000 meters is irrelevant as long as you consider the risks involved. The smaller the safety buffer, the less safe the calculation is. The larger the safety buffer, the safer the calculation is, but it also is more restrictive.

The calculation becomes less safe under several conditions.

* The farther the assumed trajectory is away from the actual trajectory, the less safe the calculation is. (The converse is true: if the assumed trajectory equals the actual trajectory, the calculation is 100 percent safe.)

* There are two possible examples of the differences between the trajectories: the assumed trajectory is generally above the actual trajectory (see Figure 7) or the assumed trajectory is generally below the actual trajectory (see Figure 8).

* The closer the final attack cone comes to the summit where it crosses the GTL, the less safe it is. This is due to the larger difference in the assumed trajectory and the actual trajectory near the summit. At the level point, the trajectories are closer together.

* The farther the VI is from zero, the more the actual trajectory becomes less like the assumed trajectory and, therefore, less safe.

The successful synchronization of supporting arms fires puts the enemy in a dilemma. If he defends against one, he makes himself vulnerable to another.

This altitude separation technique increases the fire supporter's tools available to destroy the enemy using the suppressive effects of large caliber indirect fires and the large ordnance of fixed-wing aviation while minimizing risks to the aircrew.

A more in-depth explanation of this technique and other TTPs for synchronizing indirect fires and aviation is available from the author at [e-mail].

The joint community has several broad tactics, techniques and procedures (TTPs) for separating aircraft and indirect fires, but the TTPs fall short of providing specific scenarios and calculations to fire supporters. The TTPs in this article should be adopted by the Army, Navy, Marine Corps and Air Force and move the services toward developing more JCAS TTPs.

1. Range to Target: 10,300 Meters
2. Charge: 6 White Bag
3. Target Altitude: 880 Meters (Meters X 3.3 = Feet): 2,900 Feet
4. FAC: 045 to 090 Degrees Magnetic
5. Range to Intersection of the FAC: 6,000/8,300 Meters
6. Chart Ordinates: 1,400/1,000 Meters

Chart Ordinate  Stay Above      Stay Below

<300            2000            N/A
 400            2400            N/A
 500            2700            N/A
 600            3000            N/A
 700            3400            N/A
 800            3700            N/A
 900            4000            N/A
1000            4300            2300 5,200 MSL
1100            4700            2600
1200            5000            2900
1300            5300            3200
1400            5700 8,600 MSL  3600
1500            6000            3900
1600            6300            4200
1700            6700            4600

Figure 6: Altitude Deconfliction "Cheat Sheet." For the stay-above
altitude, multiple the higher chart ordinate times 3.3 and add 1,000
feet as a safety buffer (1,400 X 3.3 + 1,000 = 4620 feet expressed up to
the next 100 feet on the cheat sheet to 5,700 feet). Then add the 5,700
feet to the target's altitude (2,900 feet) and you have the stay above
altitude of 8,600 feet at mean sea level (MSL). For the stay-below
altitude, multiple the lower chart ordinate times 3.3 and subtract 1,000
feet (1,000 X 3.3 - 1,000 = 2,300 feet). Then add the 2,300 feet to the
target's altitude (2,900 feet) for the stay below altitude of 5,200 feet
MSL.

References:

1. Joint Publication 3-09.3 Joint Tactics, Techniques, and Procedures for Close Air Support (CAS)

2. Major Donald L. Barnett, "Altitude Separation: TTPs for Artillery Fires and CAS," FA Journal, March-April 1998.

3. MCWP 3-1.6.19/FM 6-40 TTPs for Field Artillery Manual Canon Gunnery

4. MCWP3-16 Fire Support Coordination in the Ground Combat Element

5. MCWP 3-16.6 Supporting Arms Observer, Spotter and Controller

6. MCO P3500.4F Standard Operating Procedures for Range Training Areas and Airspace

7. Combined Arms Exercise (CAX) Safety Handbook, Marine Air Ground Combat Center, Twentynine Palms, California

By Captain John S. Gilbert USMC

Captain John S. Gilbert, USMC, until recently, was an Assistant Fire Support Representative in the Tactical Training and Exercise Control Group (TTECG) of the Marine Air Ground Task Force (MAGTF) Training Command (MAGTFTC) at the Marine Corps Air-Ground Combat Center (MCAGCC), Twentynine Palms, California. Currently, he is a Naval Aviatior Student, Marine Aviation Training Support Group 21 at Pensacola Naval Air Station in Florida. He also has been a Forward Observer; Liaison Officer to 2d Battalion, 3d Marines; Headquarters Platoon Commander; Guns Platoon Commander; and Assistant Executive Officer, all in C Battery, 1st Battalion, 12th Marines based at Kaneohe Bay, Hawaii. While serving with C Battery, he deployed to Okinawa twice.