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Aerial Refuelling of Airborne Early Warning and Control Aircraft

12/06/2017

The combat power of a nation is greater than the total potential of all the combat elements it possesses. This is because some combat elements magnify the potential of others. Such boosters are normally referred to as Force Multipliers. An exponential enhancement of combat power takes place by of a process that combines the effects of multiple force multipliers. 

In one aspect, such a beginning was made on November 30, 2017, when the Indian Air Force (IAF) undertook aerial refuelling of its Netra Airborne Early Warning and Control (AEW&C) aircraft from a IL78 refueller.1 Although the IL78 fleet has been operational since 2002 and the Airborne Warning and Control (AWACS) were inducted in 2009, it is only after the induction of the Embraer 145 platform based Netra earlier this year that such a combination of force multipliers has been operationalised. 

In the current operational scenario, force multipliers can be classified in three broad categories – Battlespace Transparency and Control Systems (BTCS), Range and Endurance Enhancers (REE), and Weapon Precision and Range Enhancers (WPRE) for targeting. 

BTCS include all sensors and networks that assist an accurate assessment of the location, potential and intent of all combat assets in a predefined battlespace as well as help control own assets for force application. These include ground/sea based and airborne/ space-based electronic, optical and infra-red sensors in combination with the requisite communication networks to create the battlespace awareness for friendly elements and deny the same to the hostile elements. 

Amongst these, airborne sensors are the most flexible and can be deployed in the area of interest at very short notice. Airborne sensors overcome the line of sight limitation of surface based sensors and help effective surveillance and control in mountainous terrain in particular. Airborne Warning and Control Systems (AWACS) and Airborne Early Warning and Control (AEW&C) aircraft are classic force multipliers in this category. 

REE are aircraft capable of dispensing fuel to other aircraft in the air in order to enhance the range and endurance of aerial platforms. The concept of aerial refuelling is nearly a hundred years old, with the first recorded refuelling occurring on June 27, 1923. Aviation in general and military aviation in particular has come a long way since then. Aerial refuelling helps fighter/bomber aircraft to stay in combat for a longer duration or reach targets farther than their inbuilt fuel capacity permits. It also enables them to carry more weapon load and less fuel to stay within the safe operational limits especially at high and hot airfields. 

After take-off, these aircraft take in the balance fuel from the aerial refueller as per the mission requirement. That is why, today, nearly two thirds of the fighter/bomber aircraft deployed worldwide are capable of receiving aerial refuelling. 

The profile of the Indian combat fleet is changing too. In a few years, with the phasing out of the MiG21 and MiG27 fleets, the entire Indian combat aircraft fleet will be capable of receiving aerial refuelling. However, this is not the case for wide-bodied and large aircraft. Range and endurance have rarely been an operational issue for large-bodied aircraft owing to large internal fuel carrying capability. But, when such aircraft are modified and deployed as AWACS and AEW&C, this dynamics changes. 

Effective mission duration of AWACS/AEW&C is a subset of its endurance. Transit time between the parent base and operating area and fuel required for a possible diversion during recovery has to be managed within the overall platform endurance. During hostile conditions, the base of operation is required to be in depth to minimize the risk of an enemy attack while the aircraft is on the ground for refuelling or servicing. This reduces the time AWACS/AEW&C can remain on station for operational tasks. 

In a typical AWACS/AEW&C mission profile, “On Station” duration varies between 70 to 80 percent of platform endurance. However, in case of missions over the sea and far from any friendly/safe air base, this could reduce to 30 or 40 percent. After each mission, the aircraft requires to be refuelled and serviced on the ground. This process is time-consuming and can take up to three hours. 

The combination of these two factors (on ground time and transit time to mission area) limits the effective mission duration for each platform. 

In a 24-hour cycle, an AEW&C platform will be mission effective for about 12 hours. The remainder is spent on the ground refuelling and servicing, as well as transiting to and from the operational area for each sortie. In case the aircraft is refuelled in the air, at or near its operational area, there is a major change in this mission effective time. For AEW&C, aerial refuelling for 10 minutes enhances their endurance by four hours.2 In practical terms, the mission effective time increases to 18 hours in a 24-hour cycle. Simply stated, aerial refuelling reduces the number of platforms for round the clock surveillance in a specified area with AEW&C from two to 1.33. 

This can be operationally employed by bringing a larger area under AEW&C surveillance. Resorting to multiple aerial refuelling improves this matrix further. However, this has to be within the overall limit imposed by crew fatigue as well as maintenance imperatives in terms of replenishing other consumables (oil/gases) and replacing/servicing components (due after a specified duration of operation). An additional advantage of such a profile is reduced “on ground” time. This reduces the vulnerability of large sized aircraft. This dimension is significant as large-bodied aircraft do not have hardened aircraft shelters for protection and are most vulnerable when on the ground. 

Since induction in 2002, the refueller fleet of IL78 has primarily been utilised by the IAF and the Indian Navy’s fighter fleet. Jaguar, SU30MKI and Mirage 2000 have been the major receivers. They have utilised this capability for participating in international exercises from the USA in the west to South Africa in the south and Singapore in the east. A set of additional receivers in terms of AEW&C will stretch the limited fleet. Mission planning for aerial refuelling will get more complicated trying to meet the demands of receivers planned for offensive and defensive missions and now for surveillance platforms as well. Each element would be looking for an optimal refuelling corridor as per its mission objectives. 

The requirement of all three types of missions will be concurrent but not co-located. The situation will ease as and when more refuellers are inducted. The process of increasing the fleet of refuellers has been in the pipeline for over a decade. Perhaps, the latest development with respect to the refuelling needs of AWACS and AEW&C will give the required impetus for this project. 

Aerial refuelling is considered as one of the most challenging exercises. More so in the probe and drogue method employed by the IL78.3 This method is defined as a controlled collision between the probe and the drogue. The fighter class of aircraft are inherently designed as manoeuvring platforms and have an adequate reserve of power, two attributes needed for this exercise. High momentum, limited power reserve and sluggish control response make this exercise very difficult for a transport aircraft. This is further complicated when there are additional external surfaces as in the case of the AEW&C. Operating an aircraft for a precise manoeuvre in the downwash of four-engined wide-bodied aircraft tests the skills of the aircrew. 

That is why not many air forces in the world have attempted or developed this capability. IAF has attempted this within months of operationalisation of AEW&C. With the experience gained in this exploitation, IAF will surely graduate to the more difficult task of aerial refuelling of AWACS based on the IL76 platform. Its large size and momentum, huge radome and high tail stabilizer design reduce the operational window for aerial refuelling. A very high level of precision is warranted with negligible margins. 

To truly exploit this newly tested operational capability, IAF will have to augment its fleet of in-flight refuellers and train an adequate number of aircrew, mission commanders, fighter controllers and systems operators for AEW&C for enhanced mission effective time. The in-flight refuelling of AEW&C leads to an overall enhancement of IAF’s combat potential, the multiplication effect of force multipliers. A new chapter has thus begun. 


Views expressed are of the author and do not necessarily reflect the views of the IDSA or of the Government of India. 

Date: 
12/06/2017
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Institute for Defence Studies and Analyses

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