Fuel Calculations and Diversion Airfields for Military Jets

graveyard4DCS · February 4

Hello !

I'd love to hear how you approach fuel calculations in a combat environment, and more specifically the minimum fuel for landing or in-flight refueling, a quantity of fuel that is closely linked to the diversion airfields you've chosen.

To kick-start the discussion, here's a short article introducing the concept of diversion airfields in the context of military aviation.

Enjoy your reading!

Diversion Airfields for HPMA: Introduction

In military aviation, safety and mission effectiveness depend heavily on having well-planned contingency options. Diversion airfields are critical elements in ensuring that HPMA (High-Performance Military Aircraft, i.e. fighter jets) have a safe haven in case their primary destination becomes unavailable. These airfields act as lifelines, particularly in dynamic operational environments where emergencies, adverse weather, or other unforeseen factors (like enemy military action) can disrupt mission plans. I'll introduce here the purpose of diversion airfields, the principles of fuel planning, and the additional considerations that ensure mission success, before a next article that will apply it to the Afghan case.

Diversion Airfields: Purpose and Selection

Diversion airfields are carefully chosen to meet the operational demands of HPMA. These selections are based on factors such as proximity to the mission area, runway capabilities, support infrastructure, and overall security. For military jets, runway length is a paramount consideration, as the runway must accommodate the high speeds and potential heavy payloads upon landing. The availability of military-grade fuel, maintenance services, and munitions handling facilities further influence the choice of suitable diversion airfields. In high-threat zones, security becomes an equally important factor. Diversion airfields in such areas must be secure from enemy activity and equipped with defensive measures to protect personnel and assets.

AIP page for Kabul International Airfield stating that military grade F-34 fuel is available: it's a suitable diversion option in terms of fuel.

Another crucial aspect of diversion airfield planning is the strategic placement of at least two suitable options near the primary recovery base. This ensures operational flexibility and contingency coverage, as the fuel requirements upon arrival at the primary airfield depend not only on its weather conditions but also on the conditions at these alternate diversion sites. This approach mitigates risks and enhances overall mission safety.

However, since alternate airfields choice is a risk management decision, the rules can be changed depending on the actual operational situation by a commander with the sufficient level of authority. For example, we can imagine that reducing the alternates option to a single airfield can be decided, or even to no alternate options, for carrier operations at large for example (also called "blue water ops").

Fuel Planning and Minimum Reserves

Given their high instantaneous fuel consumption, fuel planning for military jets needs to be a meticulous process that balances operational requirements with safety. The calculation begins with estimating cruise fuel burn, which is the amount needed to reach the diversion airfield under normal cruise conditions. Reserve fuel is then added to account for potential deviations, holding patterns, or emergencies. These reserves are critical, as they allow pilots to execute specific procedures after reaching the diversion airfield.

National regulations often dictate the specific procedures enabled by minimum fuel reserves. For example, in France, the minimum fuel for VMC/day operations ensures the ability to perform a go-around procedure followed by 10 minutes of low-level navigation before bailout. For IMC/night operations, the reserves account for a go-around, a second IMC procedure, another go-around, and an immediate bailout.

In contrast, civilian aviation adheres to stricter fuel reserve rules, such as carrying enough fuel to reach an alternate airport plus 45 minutes of holding time. While effective for commercial airliners, this approach is totally impractical for high-performance military aircraft. Following such rules would leave combat aircraft with virtually no fuel for combat operations. Instead, military fuel planning emphasizes adaptability, incorporating real-time mission demands and environmental conditions.

Note that additional fuel reserves are often allocated to account for local circumstances. For example, operations may require extended holding times due to heavy air traffic or regular runway closures. For example, in Afghanistan these closures could result from routine inspections, such as those conducted after mortar attacks on airfields. By anticipating these factors, mission planners ensure that pilots have the fuel needed to navigate complex and unpredictable scenarios.

Military personnel taking cover in a bunker during a rocket attack at Kandahar airbase.

Essential Diversion Data for Mission Planning

The effective use of diversion airfields relies on having accurate and comprehensive data. Inflight guides and mission planning tools need to be created in order to provide essential information to ensure safe and efficient in-flight decision-making. Key data points include:

Relative Location: information on range and heading to diversion airfields helps pilots quickly assess options. For example, Creech AFB is located 36 NM from Nellis AFB on a heading of 290°, while Edwards AFB is 160 NM away at 225° (see picture below).

Runway Dimensions: runway length and orientation are critical for landing and takeoff. Diversion airfields like Edwards AFB offer long runways (15,000 feet), while others like Creech AFB provide shorter options (9,000 feet) suitable for day/VFR conditions .

Navigation Aids (NAVAIDs): TACAN or VOR frequencies allow for precise navigation. For instance, Creech AFB operates on TACAN Channel 87 (INS), while Edwards AFB uses Channel 111 (EDW) .

Ideal Transit Altitude: specified altitudes optimize fuel consumption and air traffic deconfliction. For example, en route altitudes to diversion bases in the Red Flag exercise range from FL190 to FL250, depending on the distance .

Fuel Consumption for Transit: guides often include fuel usage for specific routes. For example, transitioning to Fallon NAS from a specified location requires 5,000 pounds of fuel with reserves .

Example of diversion data for Nellis. This picture is not specific to an aircraft type.

Understanding the assumptions underlying these fuel calculations is also vital for their effective application. Assumptions often include factors such as the aircraft’s load, weather conditions, expected airspeeds, and transit altitude. Assumptions about payload configuration will impact fuel burn rates, particularly for aircraft carrying external stores. By knowing these underlying assumptions, pilots can adjust calculations to reflect real-world conditions and adjust the fuel to the closest necessity.

Detailed assumptions made for fuel calculation by a A-10 crews for a live fire exercise.

Another important consideration is how this data is presented. Diversion data is typically displayed in either tables or graphical representations. Tables provide structured, detailed information such as range, headings, runway lengths, and fuel requirements. However, graphical presentations, such as maps with overlayed annotations or visualized flight paths, are often more effective in operational contexts. A visual representation allows pilots to quickly grasp critical information, including the relative positions of airfields and key navigation details. This is particularly useful in high-stress situations where rapid decision-making is essential. While tables remain a valuable planning tool, graphical presentations offer a clearer, more intuitive way to process information during flight operations.

Another example of divert data presented in a table: while all the information if readily available, it's certainly less easy to use in flight than a schematic representation.

These data points, combined with mission-specific factors, enable pilots and planners to make informed decisions. By integrating this information into pre-flight planning and real-time operations, military aviation maintains its focus on safety and mission success.

As a conclusion, we can say that developing accurate diversion data and graphical kneeboard pictures for every deployment base is a mandatory step to improving mission planning and in-flight diversion execution. These resources ensure that pilots can make efficient and reliable decisions, both on the ground and in-flight. In a following post, I will give you an example by as creating detailed diversion data for operations in Afghanistan, focusing particularly on Kandahar.