ISAF 2009-2013 - ACO Building - Air-to-Air Refueling Areas (2/x)

Once we have included all the civilian airspace as described in the AIP (2009 example here), we can start the ACO building by placing AAR Areas.

Let's summarize here the minimum requirements for such areas.

I. Altitude

I.1 - Vertical space

By default, a single tanker needs a 4,000 ft altitude block to operate: that's the minimal vertical extension you need to book for any AAR Area. Increasing that block with an additional 1,000 or 2,000 ft when possible will give the tanker's crew some flexibility, for example to remain VMC when cloud tops reach the Base Level.

Single tanker operations: vertical space.

If you intend to let several tankers operate in the same area, you need to allow them more vertical space. By default, a 7,000 ft altitude block will be required to operate 2 tankers in the same area.

Multiple tanker operations: vertical space.

That vertical airspace can be drastically reduced if tankers are operating in formation. In that case, vertical spacing between 2 tankers is 500 ft VMC, and 1,000 ft IMC. But since the ACO should anticipate the worst case, a 1,000 ft spacing will be used at this stage.

Multiple tankers in formation: vertical space.

As a consequence, I suggest allowing by default between 5,000 and 10,000 ft of vertical spacing for AAR Areas: it will enable you to fit multiple tankers configurations.

I.1 - Minimum refueling altitude

As discussed previously, a minimum altitude of 10,000 ft AGL for AAR operations is advised in order to remain above MANPADS and AAA threat.

For Afghanistan, it means that FL150 is generally the lowest Base Level in the south of the country, while in the North flying above FL200 is always necessary, and it's sometimes even impossible to remain above 10'000 AGL.

Note: the issue of HAAR (Helicopter AAR) or C-130 should be treated separately.

In both cases, the standard 10,000 ft AGL buffer is not compatible with their performances. The C-130 family aircraft have an optimal AAR altitude at FL100, while helicopters have a ceiling well below 10,000 ft for AAR. In fact, standard HAAR operations are supposed to take place in low altitude, from 500 to 1,000 ft AGL. However, in Afghanistan, with a widespread small arms fire (SAF) threat, remaining above 3,000 to 5,000 ft AGL is already a good preemptive measure.

HAAR Operations in DCS World, using the UH-60 mod.

Consequently, HAAR operations in Afghanistan can only be planned in the lowest regions, preferably over desert places in order to remain clear of possible SAF threat.

II. Horizontal Plane

II.1 - AAR Areas Location

As discussed in the previous post, we need to place AAR Areas out of airways and Class C and D controlled airspace.

If you did not include all the airways and civilian airspace in your ACO yet, using Skyvector's map will be very helpful: both current airways and controlled airspace clearly appears on this map, contrarily to older ONC and TPC maps that don't present them.

Skyvector map for CombatFlite.

Don't hesitate to create a lot of AAR Areas: they will be activated on demand, and are totally transparent to operations when not in use. It's better to have a ROZ already created, and not activated, than requesting a last minute ACO change to create a new ROZ!

For HAAR areas, refer to my previous posts on CSAR basing in Afghanistan. Around 2010, CSAR HH-60s were based at Bagram and Kandahar. Placing HAAR areas at the edge of their unrefueled range is a sensible choice, since that effectively doubles their operational radius. A HAAR planned near Camp Bastion, mid-way between Qalat and Ghazni, or near Mazar-e-Sharif would make most of the country directly reachable.

In red, proposed low-level HAAR areas. These positions will double CSAR helicopters’ effective operational radius.

II.2 - AAR Areas Dimensions

The question of AAR Areas dimension is theoretically not a big question. However, in DCS World, it can become an issue...

Let's start by saying that ATP 3.3.4.2 describes the Anchor pattern as a 7 to 20 Nm wide and 50 Nm long pattern.

Anchor Pattern as described in ATP 3.3.4.2

But in theaters like Afghanistan, if all areas are dedicated to "Anchor" patterns (RV Alpha), the standard patterns are generally 15' long to accommodate a 2-ship fighter flight, and sometimes 20' long for bigger formations (4-ships) or bigger receivers (like AWACS).

A quick calculation gives us more details: an 300 kt IAS at FL200 is around 450 kt TAS, or 7,5 Nm/min. At the same speed, a 15° AoB gives us a turn radius of 10 Nm, a 20° AoB 7 Nm and a 25° AoB 5.5 Nm: the width of the track will be 10 to 20 Nm large. In reality, 15 Nm is a good reference. The 2 x 360° turns normally take around 5 minutes.

For the legs, we need to accommodate the 10' or 15' remaining, i.e. 5' or 7'30" per leg. At 7.5 Nm per minute, it represents respectively 35 and 55 Nm. But that's on paper only... In reality, in Afghanistan, tankers did not abide by strict time references (or ARCT = AAR Control Time), and the leg length did not really matter... A 35 Nm length is therefore perfectly correct.

Now that we have calculated the width and length of our racetrack pattern, we just have to add some lateral buffers, and we can build an AAR Area: a 25 x 50 Nm box is perfectly able to accommodate a standard 15 minutes refueling pattern.

All 15 minutes refueling patterns can fit in a 25x50 Nm box.

But here come the difficulties of DCS World: if a tanker alone will nicely follow this track, it's not the case once it started refueling... As it has been mentioned on numerous occasions in DCS forums, our tankers currently take a roughly 10° AoB only during their turns, resulting in very wide racetracks, sometimes more than 20 Nm wide...

Tanker's track compared: more than 20 Nm wide during AAR, less then 10 Nm otherwise.

As a consequence, I suggest using the "tanker alone" behavior to create your AAR Areas, and accept that it will briefly go outside on cold leg during refueling operations. In order to minimize consequences, always put the "hot" leg along the closest factor area. In the example below, the hot leg is along the airway on the West, and the tanker will turn towards the East. Of course, if risking entering Pakistan is an issue in your scenario, you'll have to move the track further north.

Carefully choose your ARCP and "hot" leg to anticipate DCS tanker's behavior.

III. Mission Editor Setup Advice

Here are a few advice to help you make your tanker tracks more realistic:

• Tanker tracks typically have designated names, and across the theater, these names often follow a specific theme. As we've seen it previously, in 2001 AAR areas were named after figures from Greek mythology. After 2004, the new ACO adopted a “Muppets” theme, using names like Scooter, Pepe, and Clifford. Choose a theme of your own, and use it to name your areas accordingly.

• Tanker frequencies can be assigned in two ways: by callsign or by area. In general, tanker crews monitor their callsign frequency while in transit, then switch to the designated area frequency upon arrival. This ensures that if a replacement tanker is assigned in place of the original ATO tanker, the transition is seamless for receivers. Additionally, if you need to contact a tanker transiting between areas, you can reach it on its callsign frequency. It is recommended to assign one frequency per area and ensure that tankers switch to that frequency once on station.

• Tanker A/A TACAN channels are assigned in a similar manner: each area is allocated its own channel. Note that A/A TACAN normally provides range only, not bearing. Although the “Bearing” option is apparently currently non-functional, it’s good practice not to select it. Additionally, individual TACAN channels are often assigned to specific tankers in the ATO.

It's good habit not to select the "Bearing" option in tanker's TACAN options.

• Tanker speed is another recurring issue. To make it simple: the tanker will adapt its speed to the receiver, and each receiver has an optimal speed for AAR. Between two receivers, the tanker will reduce speed to its Max Endurance AOA, in order to preserve fuel. Best tanker speeds can be found in what's called "National SRD" for each country. For example, optimal FL/IAS/Mach are:

  • KC-135 + A-10A/C: 150/220/0.68

  • KC-135 + F-4A/F: 300/315/0.81

  • KC-135 + F-16: 300/315/0.81

  • KC-135 + F-15: 200/300/0.82

• Keep in mind that at FL200, indicated airspeed (IAS) differs significantly from ground speed (GS). Since GS = true airspeed (TAS) ± wind, you’ll need to convert IAS to TAS to determine the correct ground speed. I discussed some mental calculation methods in an earlier post, but using an online calculator can also be a quick and reliable option.

Optimal refueling speeds and altitudes for KC-135 and KC-130. Official recommended speeds may differ depending on aircraft versions.

Conclusion

Using the information above, you can now build a realistic AAR Area configuration for the Afghanistan theater to replicate the 2009–2013 operational environment. I will publish my own configuration in a next post.