Aerial Refuelling Options in North America and Europe

Armed forces in North America and Europe are seeking to upgrade their aerial refuelling capacity. Currently two options dominate the market.

Aerial refuelling is essential for long-range combat missions and for long distance transport flights, especially when there is limited capacity for intermediate landing. This has long been a major priority for the US armed forces, given their global commitments and the vast distances their aircraft need to cover in peacetime and in war. European nations have increasingly discovered the value of aerial refuelling as they have accepted out-of-area commitments and recognised the need for greater power-projection capabilities. Even operations in peripheral regions require this capacity, especially when tactical strike aircraft are involved, as they discovered during the 2011 air campaign over Libya.

Roughly a dozen different types of refuelling aircraft are in service in the various European nations, with another four dedicated refuelling types active with the US armed forces. In addition to dedicated refuellers, numerous large and medium transport aircraft models and even combat aircraft can be outfitted with tanker modules enabling them to serve as ad hoc refuellers on demand. However, currently only two large, dedicated refuelling aircraft models are in production, one each in Europe and the United States.

Airbus A330 MRTT

Figures published in March 2023 by the Center for Strategic & International Studies (CSIS) in Washington show that, while the European NATO partners currently own circa 160 aircraft capable of aerial refuelling operations, only a quarter of these are dedicated refuelling aircraft. The long-range refuelling capability of the European NATO partners is steadily improving through ongoing procurement of the A330 MRTT (Multi-Role Tanker Transport); 30 aircraft are currently operational in Europe, with another 10 on order. In addition to national armed forces, operators include the NATO Multinational Multirole Unit (MMU) which is actively supported by six European members of the alliance. Additional units serve with the armed forces of several Middle Eastern and Asia-Pacific nations. The Royal Australian Air Force was the first service to introduce the A300 MRTT (under the designation KC-130A) in 2011, followed by the British RAF (as the Voyager) in 2012.

The twin-engine A330 MRTT is based on the commercial Airbus A330-200. The MRTT designator reflects the fact that the wide-body plane – like other major tanker aircraft – retains the capacity to transport cargo and/or passengers, including medical evacuation (medevac) personnel across intercontinental distances. The total payload capacity is 45 tonnes, including the passenger deck and the lower (cargo) deck. The 120 m3 cargo deck itself can accommodate up to 37 tonnes, including either 27 LD3 containers or eight military pallets, as well as bulk cargo. For personnel transport, the A330MRTT can seat – depending on configuration – up to 300 passengers. In the medevac configuration the plane can accommodate 40 stretchers and 100 seated passengers (plus 20 medical staff) or up to 130 stretchers in bunk-bed configuration; alternately, the passenger deck can be outfitted with six intensive care stations while accommodating 47 seated patients and another 16 on litters.

The A330 MRTT can refuel all classes of fighter, transport, and surveillance aircraft in NATO service. For this mission, the A330 MRTT has a fuel capacity of 111,000 kg, the highest capacity of all operational tanker models. According to Airbus the plane can offload 50,000 kg of fuel to a broad range of aircraft during a four-hour loitering mission at over 1,000 NM (1,852 km) from its take-off point. In addition to operational refuelling missions the tanker can support four fighter aircraft on a 2,800 NM (5,185.6 km) ferry flight to a distant operating zone – approximately the distance from Athens to Kabul or Rome to Addis Ababa.

Refuelling operations are controlled via the onboard refuelling console which is located in the cockpit. Stationing the boom operator here enhances safety by allowing the flight crew to react immediately to unexpected developments. The digital high-definition 2D/3D Enhanced Vision System which feeds into the boom operator’s console supports both day and night refuelling and provides high resolution video recording of the refuelling operation.

The aircraft can deploy either a tail-boom system or a wing mounted probe and drogue system, depending on the aircraft to be serviced. Airbus Military’s Aerial Refuelling Boom System (ARBS) supplies receptacle equipped aircraft, including most US-designed fighters; the fuel transfer rate via the ARBS is 3,600 kg per minute. The ARBS can also be used to transfer excess fuel to another A330 MRTT via a Universal Aerial Refuelling Receptacle Slipway Installation (UARRSI) mounted atop the receiving aircraft. Cobham 905E pods can be attached under each wing for drogue and probe refuelling, which accommodates most European designed fighters as well as the F/A-18. The fuel transfer rate is 1,300 kg per minute per fuel pod. Additionally, a removable Cobham 805E Fuselage Refuelling Unit (FRU) can be mounted centreline beneath the stern to permit drogue and probe refuelling of transport aircraft such as the A400M or C295, which require a different fuel than the fighter aircraft. The FRU’s transfer rate is 1,800 kg per minute.

Since the A330 MRTT’s introduction Airbus has continued to upgrade the technology and the design to ensure state-of-the-art status. In 2020 Airbus teamed with the Republic of Singapore Air Force (RSAF) to develop the A330 SMART MRTT. According to Airbus, the new design will be the world’s first to integrate a fully Automatic Air-to-Air Refuelling (A3R) capability. It will also provide an enhanced vision system for night-time covert operations. Prototype testing is ongoing in Singapore.

Boeing KC-46A

The United States Air Force (USAF) is currently replacing its legacy tanker aircraft through a three-phase cycle initiated in 2006. Since the program’s inception the three phases have been designated KC-X, KC-Y and KC-Z. The KC-X phase was to represent extant technology and provide a readily available solution to replacing the oldest active tankers. KC-Y was conceived as a “bridge tanker” with some advanced technologies, paving the way for a revolutionary next generation KC-Z. In 2008 USAF selected the KC-45A (a derivative of the Airbus A330 MRTT, which was jointly offered by then EADS (now Airbus) and Northrop Grumman) as the winner of the KC-X competition. Following Boeing’s protest the competition was repeated. In 2011, Boeing won the contract to supply up to 179 KC-46A Pegasus aircraft.

The twin-engine KC-46A is derived from Boeing’s civilian 767 airframe. In the transport role, the plane has a maximum payload capacity of 29.5 tonnes (including up to 18× 463L pallets) or up to 114 passengers. In the medevac configuration the Pegasus accommodates 30 ambulatory and 24 litter patients, plus up to six intensive care stations. The aircraft can be converted between the three transport missions – cargo, personnel or medevac – within two hours. In addition to the tanker and transport missions, the KC-46A is designed to serve as a communications node, using the integrated data links and Advanced Battle Management System to provide tactical situational awareness to combat aircraft.

The KC-46A has a fuel payload capacity of 97,000 kg to serve US, allied and coalition forces. The aircraft is equipped with a refuelling boom for receptacle equipped aircraft; the boom is a modernised variant of the system used on the KC-10 tanker. The Pegasus also has a permanent centreline drogue system for probe-equipped fighters. Additionally, two Wing Aerial Refuelling Pods or WARPs can be carried to permit drogue refuelling, servicing two fighter aircraft at the same time. Transfer rate is 4,500 kg per minute via the tail boom and 1,500 kg per minute via either drogue system.

Unlike on earlier USAF tankers, the KC-26A’s boom operators are not seated aft; instead, the two-seat Aerial Refueler Operating Station (AROS) is located at the front of the aircraft. The refuelling process is conducted via fly-by-wire controls, guided by imagery and flight data provided via three displays on the AROS console. The imagery is provided via the Collins Aerospace high resolution Remote Vision System (RVS) which operates a number of externally cameras and sensors designed to provide a 185° stereoscopic view of the airspace below and aft of the plane.

Delayed Evolution

Unfortunately the RVS, in its original configuration, was seriously flawed. It reacted poorly to lighting changes, and tended to relay distorted images which misrepresented distances. The USAF deemed this as a category 1 deficiency. A revised RVS design was finally accepted in mid-2022. This RSV 2.0 system has two pairs of 4K ultra-high definition 3D colour day cameras and two improved infrared cameras, as well as redesigned image processors and panoramic sensors. However, supply chain issues are expected to delay serial production until October 2025.

RVS was not the KC-46A’s only issue. Technical problems surrounding the plane’s design and major subsystems delayed delivery of the first units to USAF by over a year, to early 2019. As recently as March 2023, Boeing announced that ongoing deliveries were being delayed over a supplier quality control issue related to the plane’s centreline fuel tank. To date delays, refitting and re-design measures have cost Boeing a cumulative USD 7 Bn; the firm is locked into a fixed-price development contract and therefore responsible for all expenses above the original award’s USD 4.9 bn cost ceiling.

Overall, however, Boeing and the Air Force agree that the new plane has weathered the worst of its problems. The 68 airframes currently in service with USAF conduct an average of 400 missions monthly. In 2022 the KC-46A made first deployments to the Indo-Pacific and Middle Eastern regions. The first ‘real-world’ operation was recorded in August 2022 with the refuelling of F-15Es on patrol in the US Central Command (CENTCOM) area of responsibility. The Pegasus is now officially authorised to conduct worldwide refuelling of every US military fixed-wing aircraft except the A-10; seven international aircraft types have also been cleared for refuelling. However, the KC-46A is not expected to achieve formal initial operational capability (IOC) until installation of the RVS begins in 2025. Deliveries under the KC-X contract are expected to be completed in 2029.

Moving Forward – Next Generation Air-Refuelling System (NGAS)

This notwithstanding, USAF is currently planning the next two acquisition phases. With the Pegasus approaching maturity, USAF is leaning toward skipping the re-compete for the KC-Y procurement phase, stated USAF acquisition chief Andrew Hunter on 7 March 2023. Recent Pentagon analyses predict that neither Boeing nor Lockheed Martin could develop an advanced-capability derivative of an existing airframe before the 2032-2034 timeframe, leaving a multi-year procurement gap between KC-X and KC-Y. USAF plans to decide in mid-2023 whether or not to compete the KC-Y contract, Hunter said. Many observers now expect the Pentagon to award Boeing a non-competitive contract for another 75 Pegasus tankers.

Looking forward, the Pentagon has changed the third tanker production phase’s designation from KC-Z to NGAS (Next Generation Air-refueling System). The Air force launched initial capabilities studies in January 2023, including a Request for Information (RFI) posted online on 31 January. The analysis of alternatives is set to begin in October 2023, based on the proposals received from industry. According to Andrew Hunter, the USAF is planning a full and open competition for a clean-sheet high performance tanker capable of operating in a contested environment. Hunter cited the goal of acquiring an initial increment in the mid-2030s, several years earlier than the 2040 timeframe mentioned in the RFI. Both Boeing and Lockheed Martin (working in partnership with Airbus) have announced plans to compete. In this context Lockheed Martin has already proposed to base its NGAS design on the LMXT, a further derivative of the A330 MRTT. Larry Gallogly, Lockheed’s LMXT campaign director, stated in early March 2023 that his team could potentially deliver NGAS capabilities by 2031, by working from the LMXT design. Whether this would be sufficiently innovative remains to be seen. Air Force Secretary Frank Kendall stated in January 2023 that the increased long-range threats to aircraft being devised by potential opponents could preclude a design based on a commercial airframe. “They’re not designed with a high set of requirements for survivability, for resilience. The threat’s taking that freedom away from us,” stated Kendall.

Provided below is a table summarising current aerial tanker procurements in progress:

Sidney Dean