USAF Breathing New Life Into Ancient KC-135 Tankers With This New Glass Cockpit

Digital displays and other systems, along with improved software, could keep the aircraft going for more than 80 years.

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As we’ve said many times before, one of the U.S. military’s greatest strengths is its ability to respond on short notice to crises anywhere in the world. It has that capability in no small part thanks to a fleet aerial refueling tankers give bombers, multi-role combat aircraft, and cargo planes essentially unlimited range. So, it’s no surprise that the U.S. Air Force is looking to keep at least a portion of its fleet of KC-135R Stratotankers flying for at least two more decades, if not longer.

On Aug. 25, 2017, a KC-135R from the Iowa Air National Guard’s 185th Air Refueling Wing returned to its base in Sioux City after receiving a series of upgrades to bring it up to the Block 45 standard. With the upgrade package, the tankers get completely glass cockpits with large, central digital display, as well as upgraded radio altimeters, autopilots, and digital flight directors, and upgrades for various computer modules.

“The jet that we are bringing home was built in 1958 and most of the instrumentation is original to the aircraft,” Lieutenant Colonel Shawn Streck, the maintenance commander for the 185th, said, according to Avionics. “This upgrade will put our aircraft on par with its civilian counterpart.”

The Block 45 upgrade relies heavily on commercially available systems to both reduce cost and simplify up the modification process, which takes less than two months on average. The modifications make the jets safer and more reliable, as well as just providing a good opportunity to replace obsolete gear.

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The modernized KC-135R Block 45 cockpit.

Specifically, the improved KC-135s have systems that can connect seamlessly with civil navigation and air traffic control setups around the world, allowing them to safely transit through both civilian and military air space without any undue risk of accidents. The digital computers allow ground crews to easily install software updates to keep these systems up to date, too.

On top of that, the new systems allow for the aircraft to take over some of the work KC-135 crews used to have to do manually, including transferring information from analog systems into digital ones. The updated equipment also provides more accurate maintenance alerts and data, speeding up the repair process if something breaks.

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The older KC-135R cockpit, full of analog dials and gauges, which is still in service as the Block 45 upgrades continue.

“Rather than us trying to troubleshoot and figure out what’s wrong with the system, the system is now better able to tell us exactly what’s wrong with it and what we need to replace,” Staff Sergeant Daniel Swinehart, a technician from the 507th Aircraft Maintenance Squadron, part of the Air Force Reserve’s 507th Air Refueling Wing, said in an interview in 2016. “Instead of analog gauges trying to talk with digital signals, it's all digital now, so we don’t have to convert from one to the other.”

The Air Force says these additions could keep the aircraft airworthy and capable through at least the 2040 fiscal year and possibly for another decade after that. As of 2014, the Air Force had more than 400 KC-135 in service across the active component, reserve, and Air National Guard.

The present plan is to convert the entire fleet of KC-135s to the new standard by the end of 2024. Given both the increasing age of this fleet and the high demand for its services, it’s hard to overstate the importance of the Block 45 upgrade.

The Air Force’s KC-135Rs are upgraded versions of older KC-135 models, the last of which rolled off Boeing’s production line in the early 1960s. The big change was the replacement of the older aircraft’s jet engines, four Pratt & Whitney J57s, with an equal number of more powerful and efficient CFM-56s.

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A KC-135R.

Much of the avionics and other cockpit components remained the same, just as they were when the Boeing engineers designed it in the early 1950s. Beyond the engine upgrades, there have been other, smaller upgrade programs over the years. The last of these, nicknamed Pacer Crag, ran from 1997 until 2001 and replaced various portions of the cockpit and fuel management system.

In 2001, of course, the 9/11 terrorist attacks occurred, kicking off what has now been nearly two decades of near constant conflict. Tanker support has been in high demand to support aerial campaigns across the Middle East, Central Asia, and Africa. On top of that, routine missions in Europe and the Pacific have also increased in response to a host a different security concerns, including, but not limited to international terrorism.

The KC-135 provides by far the bulk of the aerial refueling for all of these missions. The Air Force has less than 60 KC-10 Extenders, which is its other major tanker. The service, along with the U.S. Marine Corps, has a number of smaller tankers based on the C-130 Hercules cargo plane, but primarily to support helicopter operations.

So, in 2010, the Air Force began work on developing what turned into the Block 45 upgrade program. Between 2010 and 2016, the service spent more than $900 million doing the research and development on what it would take to upgrade the KC-135s, building the initial prototypes, and then starting to the kits in active, reserve, and Guard tankers, including the one from the 185th.

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One of the first two KC-135R Block 45 prototypes takes off in 2013.

The age of the aircraft meant adding the new equipment wasn’t as easy as it might sound. Engineers spent a significant amount of time working out how to fit everything into the early Cold War-era airframe.

“Gutting old wiring and then reinstalling new kits, liquid crystal display screens, and supporting equipment is a multi-person job,” Belinda Schantz, the Block 45 unit chief at Tinker, said in an interview the Air Force published in January 2017. “Complicating the installation is having to work around installed controls such as the throttle quadrant and trim wheel located in the middle of the flight deck.”

But by the end of 2016, the program had hit an important milestone, having converted 45 total tankers to the new standard. The year before, the Air Force had moved all of the upgrade work, which defense contractor Rockwell Collins provides, to a single shop at Tinker Air Force Base. 

At present, Rockwell Collins has secured more than $105 million to do the actual upgrade work, but its not clear whether this initial contract covers updating the entire KC-135 fleet. Still, this lucrative and long-term deal is probably among the many reasons why United Technologies Corporation, already a massive supplier of aircraft equipment that owns engine maker Pratt & Whitney, is interested in buying Rockwell Collins.

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A technician prepares the wiring ahead of the installation of Block 45 upgrades into the cockpit of a KC-135R.

There is a concern that at some point the KC-135’s basic structure will just give out, no matter how advanced the gear inside gets. The KC-135 turned 60 in 2016. If the Air Force does keep them in operation through to 2050, the very youngest ones will be nearly 90 years old. 

There’s also a reasonable debate to be had about the vulnerability of a decidedly non-stealthy support plane in an era of rapidly improving long-range integrated air defenses and low-observable multi-role combat aircraft. That doesn't mean that even decades into the future there won't be a role for these tankers, they will be just as useful for operations in permissive environments, tanking in otherwise well protected areas, and for testing and training purposes. 

Also, if the USAF doesn't pursue a stealthy tanker, tactics and procurement will have to be adapted to accommodate the changing realities of the modern battlefield. The KC-135 could end up receiving survivability upgrades, like electronic warfare capabilities and surveillance systems that will allow them to better understand the threats around them. Even a laser defense system is a possibility. 

Perhaps more importantly, demand has only increased while the Air Force has struggled to purchase newer tankers. Delays have plagued Boeing’s KC-46A Pegasus and it’s still unclear when the first of these will be ready for active service, let alone available in sufficient quantities to begin really easing the strain on the KC-135 fleet. 

As it stands now, the service is only expecting to purchase nearly 180 of the aircraft, with the first batch arriving in 2018, too. It's possible that contractor-operated tankers could help make up some remaining capability provided by the KC-135s, but not necessarily all of what a fleet of more than 400 planes provides.

This means that, unless the global situation changes dramatically, there will be a need for many of the KC-135s for the foreseeable future and the Block 45 upgrade will help make sure they’re ready to go.

Contact the author: jtrevithickpr@gmail.com