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By Sebastien Roblin,The National Interest
In 2018 the Air Force plans to bring its first eighteen KC-46A refueling tankers into service—paving the way for the replacements of its vast fleet of KC-135 Stratotankers that date back to the 1950s. The Pegasus should prove significantly more efficient and survivable than its predecessor, but its final rounds of testing have been bedeviled by a few persistent bugs.
his piece originally appeared in 2018 and is being republished due to reader's interest.
Sleek warbirds like the F-15 Eagle and the F/A-18 Super Hornet may attract the most attention, but these aircraft can only reach distant war zones and stay active above them for useful amounts of time thanks to a veritable horde of tanker planes. In fact, the U.S. military’s air-refueling capacity is one off its unique force multipliers—while tankers in most air forces around the globe number in the single digits to the low dozens for China and Russia, the United States operates over four hundred.
By far the most numerous tanker in U.S. service is the KC-135, an aircraft based on the venerable four-engine Boeing 707 jetliner. The type entered service in the late 1950s and, despite numerous upgrades, is showing its age. However, the Defense Department has had a rocky time finding a replacement. In 2004, the Pentagon proposed leasing tankers adapted from the Boeing 767 midsize airliner. Congressional scrutiny over this unusual arrangement eventually uncovered corruption, leading to the scheme’s cancellation.
Afterwards, Boeing proposed a revised KC-767 tanker—the KC-46—but it lost in a competition versus the Airbus A330MRTT in 2008. However, the the Government Accountability Office found that the competition had been mishandled; when it was held a second time, Boeing’s design won out.
Since then the KC-46 program has suffered some delays and cost overruns—taxpayers have footed $4.82 billion so far, while Boeing has taken on $2.9 billion—but it looks like development is finally nearing completion.
Tanker of the Future
The Pegasus is based on the 767-200 widebody airliner, though it incorporates technology from the -300F and -400ER models, and even the digital “glass cockpit” of the 787 Dreamliner. The new tanker can carry up to 212,300 pounds of jet fuel—only slightly more than a KC-135. However, because the Pegasus’s two turbofans are more fuel efficient than the Stratotanker’s four, it can effectively distribute more to thirsty warplanes. To put things in perspective, an F-15 Eagle can carry around thirteen thousand pounds of internal fuel, or three times that amount if maxing out external drop tanks.
The KC-46A sports no fewer than four refueling systems to ensure compatibility with a wide spectrum of aircraft types: two wing-mounted “probe and drogues” (they resemble long hoses with a conical “basket” at the end), a third drogue under the belly and a more rigid, extendible refueling boom.
Rather than peering out at incoming planes from a special station on the belly of the plane, Pegasus boom operators sit near the cockpit and use fly-by-wire controls and remote 3D cameras to guide the probes and booms to intercept the refueling probes of friendly aircraft. A Pegasus can refuel up to three aircraft at once, pumping them full of four hundred gallons of fuel per minute on each drogue and 1,200 gallons per minute using the boom.
You can see how the Pegasus’s remote operator’s station works in this video, which depict both boom and probe refueling.
The KC-135 and KC-10 tankers are also frequently assigned cargo-hauling duties—and the Pegasus is designed from the outset to perform such missions much more efficiently. While a KC-135 can carry eight standard cargo pallets and thirty-six personnel in the hold, a KC-46A can cram up to eighteen pallets or fifty-six seated personnel—or up to 114 with some standing. The Pegasus is also designed to perform medical evacuation missions, with accommodations and power outlets for up to fifty-eight litters.
The KC-46 is also designed to be more survivable in the event of a high intensity conflict with near-peer enemy. This is accomplished through the addition of armor around the cockpit and fuel tank, a large-aircraft infrared countermeasure (LAIRCM) system to decoy heat-seeking missiles, and a Radar Warning Receiver to alert the crew if they are being targeted by enemy weapon systems.
These additions are important because potential adversaries are well aware that refueling tankers and radar planes form the logistical sinew that keeps U.S. fighters in the air and on target. While tankers would try to remain far “backfield” of the action in the event of a major air war, both China and Russia are beginning to field small numbers of stealth fighters that could be used to sneak past fighter screens to pick off support planes. There are also specialized extra-long-range air-to-air missiles such as the Russian R-37 (range: over two hundred miles) designed to snipe low-maneuverability targets while safely out of reach of their escorts.
Scratchy Refueling Booms, Dodgy EMP Tests, and Sparky Radios
By December 2017, the Pegasus had already undergone 2,300 hours of flight testing, and refueled numerous aircraft including an F-16, a Marine AV-8B Harrier jump jet, a C-17 Globemaster cargo plane, an A-10 Thunderbolt attack jet, a Navy F/A-18 Super Hornet and even another KC-46 tanker. However, an annual Department of Testing & Evaluation report reveals that certain niggling flaws have persisted despite the tanker’s imminent entry into service.
The most notable is that the boom refueling system continues to have accuracy problems. Sometimes, boom operators have impacted the receiving aircraft, often without realizing it. On other occasions, the boom has extended outward for no apparent reason after completing a refueling. In either case, this has the effect of scratching receiving aircraft, which is particularly problematic for stealth fighters, which are coated with expensive radar-absorbent materials. (Note that none appear to have tested refueling with a KC-46 so far.) This problem may in part be due to operator unfamiliarity with the new remote viewing system, though Boeing claims it is implementing a software fix to correct the issue.
A second concern is that while the KC-46 passed a test to see whether it could remain airborne after withstanding a six-decibel electromagnetic pulse (EMP), it hasn’t been verified whether it could still perform its aerial refueling mission after such a shock. The report acerbically notes that the Pegasus’s refueling, communication and defensive systems were removed prior to the EMP test, meaning there was no way of knowing whether they would still have remained functional. This at least gives the impression that those carrying out the test feared that valuable equipment could be damaged.
Nuclear detonations can create a significant EMP effect, and the Pentagon wants its tankers to remain mission capable in a nuclear-war scenario. In such an event, tankers might provide the only refueling available to key command aircraft such as Air Force One or an E-6 “Doomsday plane.”
A third issue noted by some sources is that the KC-46 has a high-frequency radio that uses the plane’s metal skin surface as an antenna. This can generate sparks and arcs that could have scary results when pumping hundreds of tons of jet fuel into another plane. Therefore, engineers are looking for an extra-secure system for rendering the radio inert during refueling operations.
Despite these problems, the new tankers are on track to enter service in the next few months. By October 2018, there should be eighteen operational KC-46As at McConnell and Altus Air Force Bases.
Currently, the Pentagon plans to acquire 179 KC-46As for $44 billion dollars and have them replace the oldest KC-135 airframes. This comes out to $245 million per airframe, compared to around $212 million for a civilian 767. Japan has also ordered three KC-46s for its self-defense force, and the aircraft may be considered for service with the air forces of Canada, India and Indonesia as well.
As plans for a more advanced KC-Y tanker have been shelved, there could be additional orders for more Pegasuses as more KC-135s age out in coming decades. If this comes to pass, the new tankers may remain active through the end of the twenty-first century.
Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing and refugee resettlement in France and the United States. He currently writes on security and military history forWar Is Boring. This piece originally appeared in 2018 and is being republished due to reader's interest.