The Air Force expects to finish qualification testing of the new engines planned for the B-52 Stratofortress by the end of 2024.

And the service plans to make a Milestone B decision on the Commercial Engine Replacement Program by the end of the summer, which would allow it to move into its engineering and manufacturing development phase, officials said in an interview with Defense News.

These developments will mark critical milestones in the Air Force’s effort to upgrade its fleet of 76 Cold War-era B-52s with new engines, radar, avionics, and other improvements to keep it flying until perhaps 2060, about a century after the B-52H was first introduced. The planes’ 1960s-era TF33 engines are at the end of their working lives, and are to be replaced by Rolls-Royce’s F130 engine.

Col. Scott Foreman, B-52 system program manager who oversees the bomber’s sustainment and modernization efforts at Tinker Air Force Base in Oklahoma, and CERP program manager Lt. Col. Tim Cleaver said in the interview that the base is also taking several steps to prepare for the significant modernization work.

This includes plans to build a massive hangar at Tinker starting in 2026, which could house up to four B-52s and increase the amount of work that can be done on the bomber at any given time.

The Air Force wants to “get these H models converted to [B-52]J models as quickly as possible, because … the clock’s ticking on those TF33″ engines, Cleaver said.

The Air Force knows the F130 engine works, Cleaver said, since a version of it has powered the Gulfstream G650 business jet for years. But the F130s will be mounted differently on the B-52, and the Air Force needs to make sure there aren’t any surprises with the bomber’s twin-pod, under-wing configuration.

Rolls-Royce last year completed much of the initial twin-pod testing of the F130 engines at NASA’s Stennis Space Center in Mississippi, Cleaver said, and the last six-week test cycle there is expected to start in early March. Those tests will involve exposing the engine pods to cross-wind blowers, and seeing what happens if one engine in the pod has to operate at reduced power or is even inoperative.

More tests will follow, Foreman said. In April, the F130 will start sea-level performance testing on a stand at a Rolls-Royce facility in Indianapolis. Another engine will undergo durability testing through 2025, Cleaver said. And this fall, F130 testing will move to the Arnold Engineering Development Complex in Tennessee, where it will be subjected to simulated altitudes to produce more data on how it might behave in flight.

Once that round is done, they said, the F130 will have finished its qualification testing that ensures it would be safe to fly, and pave the way for test modifications to begin.

The first two test B-52s will be modified at Boeing’s San Antonio, Texas facility beginning in 2026. It will take a few years to upgrade these bombers for the first time, Cleaver said, and ground and flight tests will go from late 2028 to 2031.

After this year’s testing, Boeing will set up four systems integration laboratories to ensure adding the new engines onto the B-52 will go smoothly, Cleaver said. Three will be in Oklahoma City, near Tinker Air Force Base, and the fourth — focusing on the engines’ electrical systems — will be at a Boeing facility near Seattle.

“We have a mix of simulated functions and hardware … functions to make sure that our systems are working with each other, and that we’re not using the test aircraft as our place to find problems,” Cleaver said. The labs “will really prove out the design before we even cut into a jet.”

The Air Force is still awaiting cost estimate updates from Boeing — which originally built the Stratofortress and is the prime integrator on the upgrade program — before it can finalize its own cost expectations and make a Milestone B decision, Cleaver said. Boeing is expected to provide those updates around late spring or June.

In a statement, Boeing confirmed the Air Force’s statements about the need for updated cost estimates.

The engine contract with Rolls-Royce is worth $2.6 billion; when the development, integration, test and production of other major subsystems is factored in, the cost estimate is roughly $12.4 billion.

Tinker, where all production B-52Hs will be upgraded into B-52Js, is also preparing for its role in the massive modernization effort.

“It is a large scope of work, when you include things like the radar modernization program, the [engine upgrades], integration of advanced extremely high frequency communications, [and] other programs,” Foreman said.

Tinker’s workforce will install the engines, radar upgrades, and other modernizations on B-52s as they cycle through their regular depot maintenance that occurs every four years, Foreman said.

The Air Force sends about 17 B-52s through Tinker for major maintenance each year, and wants to conduct as many upgrades to the bomber as possible as it moves through the depot. But he cautioned some modernization programs are moving at different timelines and all may not be ready when some bombers go through.

“We have a master plan that goes tail by tail, that shows over the next 10 years where [a bomber] is going to get modifications along the way,” Foreman said. “So as we get into the late [20]30s, we have a fleet of 76 aircraft with new engines, new radar, new [weapons], communications, etc. … The plan is ever-evolving as we gain more and more information and individual [modernization] programs move left or right.”

But the upgrades will mean a lot more work, and require a lot more capacity at Tinker, Foreman said. So in 2026, Tinker will start building a massive structure known as the bomber agile common hangar that could house four B-52s and allow for more upgrading work to be done. That hangar will be ready at the end of 2030, in time for the upgrades of production jets to begin in early 2031.

“If you have aircraft that are using depot docks for a longer period of time, you need more docks, and that’s what the agile common hangar brings to us,” Cleaver said.

Foreman said it typically takes a B-52 between 220 and 260 days to go through depot maintenance, depending on parts availability and whether a bomber has any age-related stress fractures or corrosion that need to be repaired. The Air Force is still trying to figure out how much more time the upgrades might add to that schedule, he said.

Cracking and other structural issues are common on the six-decade-old B-52, Foreman said, and sometimes require components to be replaced. But the Air Force is used to catching and fixing those problems, he said, and the aircraft should be able last well into the 2050s — perhaps to 2060 — without more in-depth structural upgrades.

“We’re very disciplined about [structural integrity] inspections every time [the B-52] comes in” to the depot, Cleaver said. “That’s what’s allowed this aircraft to make it here into the 2020s. But he still has life to take her into 2050 and beyond.”