Redesign to cure acoustic engine phenomenon linked to A220 failures
Redesign to cure acoustic engine phenomenon linked to A220 failures
By David Kaminski-Morrow5 March 2021
Pratt & Whitney is aiming to introduce redesigned bleed-valve ducts for Airbus A220 engines by the fourth quarter of this year, to eliminate a resonance phenomenon linked to a series of powerplant failures.
Four instances of PW1500G low-pressure compressor stage-one rotor separation, affecting A220-300s operated by Swiss and Air Baltic, occurred in the seven months between July 2019 and February 2020.
Engine parameters at the time of each failure, and the resulting damage, was “consistent” for all the events, says the US National Transportation Safety Board, which has completed an investigation into the first incident, involving a Swiss A220 (HB-JCM).
The aircraft’s left-hand engine failed as it climbed through 32,000ft over Perrigny-sur-Armancon in France while en route to London Heathrow. Examination of the twinjet after it diverted to Paris Charles de Gaulle revealed a hole in the low-pressure compressor casing and the stage-one rotor was missing.
Source: NTSB
Analysis of the failed engine from HB-JCM traced the rotor fracture to resonance
Investigators conducted multiple tests including computational fluid dynamic and acoustics analysis to identify the cause of the failure.
These tests identified a mechanically-coupled mode excitation between the stage-one and stage-three rotors of the low-pressure compressor, driven by an “acoustic coincidence” with the 2.5 bleed-valve duct cavity.
At high engine speeds in specific operating conditions, says the inquiry, the low-pressure compressor rotor blade tips could cause turbulent airflow that generated an acoustic tone as it passed over this cavity, which is situated immediately behind the compressor.
This tone excited a stage-three rotor blade bending mode which was then mechanically transferred, through the low-pressure compressor module, to the stage-one rotor – generating a bending mode in that rotor which exceeded the stress limits on its blades.
The stresses created cracks in the blade root and rotor which worsened until the rotor failed from overload.
Source: NTSB
Damage to the low-pressure compressor case resulting from the rotor failure
Three of the A220 engine failures involved the PW1524 variant of the powerplant while the other occurred to a PW1521.
Investigators determined that a software revision to the electronic engine control, which altered the compressor’s variable inlet guide vane schedule, increased the likelihood of blade-flutter onset.
Operating restrictions – including a thrust limitation at high altitude – were imposed on A220s in the aftermath of the engine failures to reduce the chances of the phenomenon being initiated, and amended engine-control software was also introduced to restore the original vane schedule.
But Pratt & Whitney is also modifying the geometry of the 2.5 bleed-valve duct, says the inquiry, in order to increase frequency margins and eradicate the problematic resonant response. It adds that the redesigned hardware is scheduled to be available by the fourth quarter.
Fuel did not feed PW4000 engine fire following engine failure: NTSBFuel did not feed PW4000 engine fire following engine failure: NTSB
A Boeing 777-200 engine fire following an engine failure last month was not fed by fuel and burned outside the core of the Pratt & Whitney PW4077 turbofan.www.flightglobal.com
By Jon Hemmerdinger6 March 2021
A Boeing 777-200 engine fire following an engine failure last month was not fed by fuel and burned outside the core of the Pratt & Whitney PW4077 turbofan.
That is according to the National Transportation Safety Board (NTSB), which on 5 March says the pilots were successful in shutting off fuel to the badly damaged engine.
Source: National Transportation Safety Board
Fire damage to the inboard side of the 777-200 PW4077 engine that failed on 20 February 2021
In an investigation update, the NTSB also reveals more details about the incident and says investigators found evidence of metal fatigue on the engine’s failed fan blade.
The 20 February incident involved a United Airlines 777 (registration N772UA) operating flight 328 from Denver to Honolulu.
“Initial examination of the right engine fire damage… found it was primarily contained to the engine’s accessory components, thrust reverser skin and composite honeycomb structure of the inboard and outboard thrust reversers,” the NTSB says.
Early after the accident, the agency said it was seeking both to understand why the engine failed and why it remained on fire following the failure.
Source: Screenshot of Twitter post by Marc Sallinger, @marcsallinger
Video of a PW4077 engine failure on 20 February 2021. The engine was powering a United Airlines 777-200.
“The spar valve, which stops fuel flow to the engine when the fire switch is pulled in the cockpit, was found closed. There was no evidence of a fuel-fed fire,” the NTSB says. “Examination of the engine accessories showed multiple broken fuel, oil and hydraulic lines, and the gearbox was fractured.”
The engine’s aft cowling “appeared to be intact and undamaged, and all four pressure relief doors were found in the open position”.
Shortly after taking off from Denver, at about 12,500ft altitude and travelling at about 280kt (519km/h), the pilots of United flight 328 “advanced power” to limit the amount of time the aircraft would be flying through turbulence.
“Immediately after the throttles were advanced a loud bang was recorded on the [cockpit voice recorder],” the NTSB says. Information from the flight data recorder indicates “the engine made an uncommanded shutdown”.
The pilots declared an emergency and “discharged both fire bottles into the engine”. Needing to get on the ground quick, they did not dump fuel, the NTSB says.
On the power of a single engine, the captain piloted the aircraft back to Denver, landing without injuries to any passengers or crew.
Examining the engine, investigators found one blade “was fractured transversely across the airfoil about 5in above the base of the blade at the leading edge and about 7.5in above the base of the blade at the trailing edge”.
Source: National Transportation Safety Board
Damage to fan blades of a United Airlines Boeing 777-200’s PW4077 engine, which failed in flight on 20 February 2021
“Preliminary findings from the scanning electron microscope examination have identified multiple fatigue fracture origins on the interior surface of a cavity within the blade,” the NTSB says. “The blade’s fracture surface was consistent with fatigue.”
When the blade failed, the engine had been in service for 2,979 flight cycles since its previous inspection. It had undergone thermal acoustic image (TAI) inspections in 2014 and 2016, and the 2016 data had been re-examined in 2018 following a similar inflight failure that year of a 777’s PW4000, the NTSB notes.
On 22 February, P&W issued a “special instruction” that calls for affected engines’ fan blades to undergo TAI inspections at 1,000-cycle intervals. The following day, the US Federal Aviation Administration issued an emergency order requiring airliners to complete the inspections before further flight.
Source: National Transportation Safety Board
This PW4077 turbofan, powering a United Airlines 777-200, failed in flight on 20 February 2021
Pratt & Whitney Makes Hypersonic Revival As Pentagon Pushes ReusePratt & Whitney Makes Hypersonic Revival As Pentagon Pushes Reuse | Aviation Week Network
A secret program inside GatorWorks seeks to deliver a high-speed, reusable propulsion system.aviationweek.com
Guy Norris Steve Trimble March 05, 2021
The turbo-ramjet configuration of the J58 engine inspires the reusable, high-speed propulsion technology for Pratt & Whitney’s Metacomet program.
Credit: U.S. Air Force
As reusable hypersonic propulsion rises up the list of U.S. Defense Department priorities, Pratt & Whitney now confirms it is working on a secretive development program called Metacomet aimed at solving the problem of fielding high-speed, reusable propulsion systems at low cost.
Already at least two years old, Metacomet—a name linked to a 17th century Wampanoag chief, the namesake of a ridge overlooking a Pratt & Whitney research facility in Connecticut—marks the company’s return to Mach 3-plus propulsion nearly a decade after selling its scramjet pioneer Rocketdyne arm to the parent company of Aerojet in 2012.
With the intellectual property of the former Rocketdyne off limits, Pratt & Whitney’s GatorWorks division—a prototyping unit formed in 2018—launched Metacomet to focus on low-cost alternatives to ramjet and scramjet propulsion for high-speed flight.
- Metacomet leverages SR-71 engine architecture
- Pentagon strategizes for reusable hypersonic push
- NASA, commercial sectors offer new options
The effort draws on the company’s expertise with gas turbine combat engines, and in particular reaches back to decades-old experience with the unique J58 engine developed for the Mach 3-plus Lockheed SR-71. That aircraft achieved sustained flight above the Mach cutoff point of a normal turbojet by diverting inlet air from the compressor directly into the afterburner.
“The faster you go, the larger the propulsion system is relative to the vehicle and how much payload and fuel you can actually fit in,” says David Stagney, senior director of GatorWorks. “So, we have spent a lot of time going back to the fundamentals and thinking about how to solve that problem differently. We know the Air Force wants to go really fast. They also want to have some very low-cost solutions, and to be able to have a large quantity of vehicles.”
As a result, Stagney says Pratt & Whitney is tackling the problem from a new perspective. “We think that we can provide unique capabilities building on the legacy we have from the Mach 3 engine that we built [several] decades ago,” he says. “Those core skills are still there, and our goal in GatorWorks is to come up with a whole portfolio of different solutions for a range of high-Mach solutions.”
The engine-maker believes its design approach, which is thought to be tailored to higher speeds above Mach 3 but below Mach 5, is simpler and more affordable because it avoids the need for pure ramjet/scramjet cycles or the complexities of mode transition to and from turbine power.
“Obviously, there are trade-offs between speed, range, cost and the amount of payload that you can take and fit onto a vehicle that makes sense economically,” Stagney says.
Metacomet appears to blur the normal distinction between “high-supersonic” and “hypersonic” regimes. Describing hypersonic as anything that travels faster than Mach 5 is a widely accepted definition—albeit arbitrary. To air vehicle designers, a hypersonic condition refers to a range of aerodynamic and thermal effects that arise at different speeds above Mach 5. They vary depending on the vehicle design and flight profile of the vehicle. These effects strongly influence the materials and shaping of the airframe, as well as the type of propulsion that is possible.
Stagney’s remarks about Metacomet suggest the program is pursuing engine configurations that can approach or exceed the arbitrary speed definition of the hypersonic term, but fall short of encountering the special aerodynamic and thermal effects at a system level.
“We’ve come up with some really unique different solutions to that problem across the whole spectrum of speeds,” he adds. “We want to offer different solutions that aren’t being thought about right now and that are much lower cost per effect.”
The work is particularly focused on reusability and a scalable architecture that can be applied to suit varying mission priorities across a combination of different sizes, payloads, ranges and speeds.
Although the company declines to provide specifics of the Metacomet solution set, test plans or potential applications, Stagney says the Air Force Research Laboratory’s (AFRL) proposed Mayhem demonstrator vehicle for a hypersonic, air-breathing propulsion system “is definitely one of the programs that we’re looking at, for sure.”
The AFRL revealed plans for the Mayhem System Demonstrator on Aug. 13 as a “larger-scale, expendable, air-breathing, hypersonic, multimission” platform that can carry “larger payloads over distances further than current hypersonic capabilities allow,” according to a formal request for information that was released to industry.
Despite its vintage, the J58, which was developed in the 1960s and retired when NASA ended test flights of the SR-71 in 1997, remains one of the most successful and ingeniously designed high-speed air-breathing engines.
While the engine’s close integration with the SR-71 airframe played a key role, the bulk of its success can be attributed to the aero-mechanical features of the J58 turbojet itself. These included axisymmetric mixed compression inlets and airframe-mounted, convergent-divergent blow-in door ejector nozzles—all aspects that could potentially be further developed for 21st-century applications.
The J58’s inlet spike, which translated longitudinally depending on Mach number, controlled the throat area and provided a stable shock structure across the speed range close to Mach 3.3. Above Mach 2.2 some airflow was bled from the compressor and fed through bypass ducts into the augmenter, transitioning the engine from a pure turbojet into a turbo-ramjet. At design cruise speed around 70-80% of the net propulsive force is derived from flow compression pressure on the spike.
However, as the turbine section was still partially interacting with the flow path, the maximum speed was governed by aerodynamic heating of the flow and the 800F temperature limit reached shortly after Mach 3.2. Aerodynamic analysis has indicated that the inlet design has the potential for operating at speeds up to and beyond Mach 5. Moreover, a configuration based on the J58 could go significantly faster than Mach 3.3 if modern materials and advanced cooling systems were incorporated to expand the temperature limits in the compressor.
Another potential area of improvement would be the modulation of the inlet flow and boundary layer. Other inlet controls in the J58 included the forward and aft bypass doors and the cowl and spike bleeds—which controlled boundary layer growth.
Later in service, including the final operational phase with NASA, the introduction of a digital automatic flight and inlet control system to orchestrate the position of the engine spikes and forward bypass doors had virtually eliminated the problem of inlet unstarts that hampered the aircraft in its early operation. Further improvement in control, and therefore performance, could be possible through the introduction of modern processors and faster actuators.
For additional performance growth, an updated J58 cycle could also conceivably provide a step toward higher Mach numbers. Options would include changes to the compressor design, materials improvements and adding supersonic combustion capability in the afterburner section. This radical redesign would also likely include fully closing off the turbine section for the maximum cruise condition.
Pratt & Whitney may also be dusting off J58 upgrade concepts studied in the late 1990s, when NASA evaluated boosting performance of the SR-71 to support its potential use in launching high-speed research vehicles and carrying captive experimental packages to higher speeds and altitudes. Some of these additional concepts involved increasing turbine exhaust temperature, raising compressor rotor speed, augmenting afterburner flow, and modifying compressor bleed and inlet guide vane schedules.
Lockheed Martin’s 2013 concept for the SR-72 could leverage a high-speed, reusable propulsion system for surveillance and strike missions. Credit: Lockheed Martin
Pratt & Whitney’s pursuit of a reusable, high-speed propulsion system comes as the Defense Department’s Research and Engineering (R&E) branch starts to look beyond the initial rush to field multiple prototypes of offensive and defensive hypersonic weapon systems within this decade. If the push materializes into a new development program, the Defense Department could support the first reusable, operational system since the cancellation of the Lockheed Martin X-33 suborbital technology demonstrator in 2001.
The R&E branch is now developing a strategy to field reusable hypersonic systems to serve the strike and intelligence, surveillance and reconnaissance missions, as well as the first stage of a two-stage system for rapid access to orbital space, a Pentagon spokesman says.
The strategy document introduces the third element of the Pentagon’s wider plans for hypersonic technology.
Expendable missiles expected to be fielded within the next 2-5 years—such as the Lockheed Martin AGM-183 Air-Launched Rapid Response Weapon, the Army’s Long-Range Hypersonic Weapon, the Navy’s Intermediate-Range Conventional Prompt Strike and the Air Force’s Hypersonic Attack Cruise Missile-—comprise the first element. The Missile Defense Agency’s plans to deliver a terminal interceptor against hypersonic missiles in the mid-2020s, followed by a Glide Phase Interceptor in the late 2020s, represent the second element.
In addition to Mayhem and Pratt & Whitney’s offerings, the Defense Department also continues to develop a turbine-based combined-cycle engine. The Advanced Full-Range Engine, a project sponsored by DARPA and the Air Force, combines an off-the-shelf turbine engine—for flight up to Mach 2.5—with a dual-mode ramjet engine capable of supersonic combustion to reach speeds greater than Mach 5.
The path to reusable hypersonic propulsion also includes civil and commercial programs. NASA’s aeronautics research arm, for example, has launched the Hypersonic Technology project, which includes a special focus on reusable vehicle technologies for the airframe and propulsion system. The Air Force’s AFWerx innovation unit also is conducting market research on a proposal to provide financial and engineering support to commercial companies developing hypersonic passenger jets under the Vector Prime program.
The AFWerx effort could give a boost to several companies, including Reaction Engines and startup Hermeus.
“We are glad to see that initiative gaining momentum,” says Hermeus CEO AJ Piplica in an interview. “In our past lives, we’ve certainly been able to benefit from that kind of situation where the government opens up test facilities—whether it’s ground test or flight test—and then partners with commercial industry to generate data in new parts of the flight regime that we’ve never been in before.
“Being able to do that for supersonic and hypersonic flight could really provide some acceleration to both the industry and an Air Force road map for reusable hypersonic flight that is currently 15-20 years out,” Piplica adds. “So, if by partnering together with industry we’re able to shave 5-10 years off that road map, that would be a major win for the country.”
Guy Norris
Guy is a Senior Editor for Aviation Week, based in Los Angeles. Before joining Aviation Week in 2007, Guy was with Flight International, first as technical editor based in the U.K. and most recently as U.S. West Coast editor. Before joining Flight, he was London correspondent for Interavia, part of Jane's Information Group.
Steve Trimble
Steve covers military aviation, missiles and space for the Aviation Week Network, based in Washington DC.
Japan Airlines Permanently Grounds PW4000-powered 777s
by Gregory Polek
- April 6, 2021, 1:16 PM
Japan Airlines has decided not to return its 13 Pratt & Whitney PW4000-112-powered Boeing 777s to service following their suspension of operations due to recent in-flight engine failures, including a December 4 incident involving a JAL 777-200. The airline had planned to retire its Pratt-powered 777s by March of next year but has accelerated their removal in favor of service with Airbus A350-900s on domestic routes out of Osaka and shift other aircraft flying international service to maintain frequencies on flights within the country.
Japan grounded a total of 31 PW4000-112-powered 777s flown by JAL and All Nippon Airways on February 21, a day after a United Airlines 777-200's PW4000-112 failed soon after taking off from Denver on a flight to Honolulu. U.S. investigators found evidence of fan blade metal fatigue in the PW4000-112 engine that failed, raining nacelle debris over a mile-long area of a Denver suburb.
National Transportation Safety Board examinations found one blade fractured at the root, an adjacent blade fractured at about mid-span, and a portion of one embedded in the containment ring. The remainder of the blades showed damage to the tips and leading edges.
The NTSB continues to investigate the relationship between the latest PW4000 failure and previous events, such as a 2018 incident in which another of the engines in a United Airlines 777-200 suffered a fan blade failure on approach to Honolulu.
In the 2018 incident, investigators determined that a fractured fan blade caused the failure. Last year the NTSB determined that insufficient training for a thermal acoustic imaging (TAI) inspection process developed by Pratt & Whitney led to technicians misdiagnosing a problem with the fan blade that ultimately failed in the 2018 incident. Since then Pratt & Whitney developed a formal training curriculum for the inspections. The FAA issued an airworthiness directive in March 2019 requiring repetitive inspections of all PW4000s in service.
Meanwhile, Japanese investigators continue their probe into the case of a PW4000 failure that involved a Japan Airlines 777-200 flying from Naha Airport in Okinawa to Tokyo Narita Airport. That airplane also landed safely after returning to Naha Airport.
“We will continue to fully cooperate and respond to the investigation by the Japan Transport Safety Board to determine the cause of the incident,” said JAL in a statement.
Turkey’s removal from F-35 program to cause hike in engine price
By the end of the year, Turkey will no longer supply parts for the F-35's engine.www.defensenews.com Turkey’s removal from F-35 program to cause hike in engine price
By: Valerie Insinna 23 hours ago
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A Pratt & Whitney F135 engine, used to power the F-35 Lightning II fighter aircraft, undergoes testing at Arnold Air Force Base in Tullahoma, Tenn. (PRNewsfoto/Pratt & Whitney)
WASHINGTON — The cost of the F-35′s engine is set to increase by 3 percent due to Turkey’s removal from the program in 2019, the head of Pratt & Whitney’s military engines division said Thursday.
The company’s F135 engine — which is used in all three variants of the Lockheed Martin F-35 joint strike fighter — was initially manufactured with a total of 188 parts produced by Turkish suppliers, Matthew Bromberg told lawmakers during a House Armed Services Committee hearing.
“These are some of the most critical parts of the engine, and the Turkey suppliers were high-quality, low cost,” he said. “Seventy-five percent of them have been qualified in new suppliers. Most of those are domestic here in the United States.”
Pratt & Whitney expects to have the remaining 25 percent of Turkish-made parts for the F135 qualified by the end of 2021, with all Turkish parts flushed from the system by the time engines for the fifteenth lot of aircraft roll off the line in 2020. At that point, about 20 percent of the F135′s parts will be made by international vendors.
Turkey, once a partner in the F-35 program set to buy 100 F-35A conventional takeoff and landing models, was expelled from the program after accepting delivery of the Russian S-400 air defense system. At the time, the Pentagon hoped to remove all Turkish suppliers from the program by 2020, but it will take until 2022 for all contracts with Turkish companies to come to a close, said Greg Ulmer, head of Lockheed’s aeronautics programs.
The Pentagon’s F-35 joint program office is “continuing to work with Pratt and Whitney on steps to address the projected cost growth to ensure that the F135 Propulsion System remains affordable component of the F-35 air system,” F-35 program executive Lt. Gen. Eric Fick stated in written testimony to lawmakers.
Aside from the forthcoming engine cost increase, the F-35 program is also grappling with difficulties in sustaining the F135 due to a power module shortage.
On April 22, a total of 21 Air Force F-35As were grounded due to engine problems, said Brig. Gen. David Abba, who leads the F-35 integration office. Fifteen of those aircraft would be flyable with engine repairs.
In a March interview, Bromberg told Defense News that a complicated array of factors had caused the engine shortage — which was further exacerbated by the COVID-19 crisis — and it would take time for corrective actions to take effect.
Unlike most fighter engine programs, where a spare ratio of about 20 to 30 percent is maintained to ensure parts are available on the flight line or the depot, the F-35 program funds a spares ratio of only about 10 to 12 percent, he said.
“The whole program was designed to eliminate intermediate maintenance and have a very robust international sustainment depot system that will be able to turn modules very effectively in the field,” Bromberg explained. “The lower spares ratio, though, is making all that a little bit more exposed than you would have seen on another program. And we have to get through that.”
Another issue is that much of the planning and funding of spare parts, repair activity and logistics processes years before it is actually needed. For a program like the F-35, which has only been operational for a couple years, those plans were based on estimates — not hard data from decades of flying and maintaining the plane.
That analysis left Pratt & Whitney a bit late when it came to fielding certain support equipment and technical data, which Bromberg said has since been delivered. On top of that, the COVID-19 pandemic added about three months delay to the company’s plans to ramp up engine production and sustainment efforts.
“We pick our best estimate. In some cases, you’re over. In some cases, you’re under. All that was in place a years ago,” Bromberg said. “But in light of 2020, we probably didn’t have enough margin.”
The F-35 program is beginning to see increased output of F135 power modules due to the arrival of needed support equipment and technical data, Fick said. The F135 engine depot at Tinker Air Force Base, Okla., plans to end a second shift by the end of the year, and the program office is also working to accelerate the stand up of F135 engine maintenance at the Fleet Repair Center South East in Jacksonville, Fla.
“The actions we have taken to date have begun to show benefit, as power module production at the Oklahoma City Air Logistics Complex has increased significantly in the last year and the projected readiness impacts, while still above our requirement, have started to stabilize,” he said.
The Tinker depot plans to produce 40 power modules this year and ramp up to 60 modules in 2022, Abba said.
However, because the services will begin conducting 2,000 hour overhaul inductions in 2022, the program office estimates the costs to maintain the F135 will grow over the next five years, Fick stated.
Pratt & Whitney Hybrid-electric System To Fly in a Dash 8 in 2024 | AIN
The governments of Canada and Quebec have committed to providing half of a C$163 million investment in Pratt Canada’s hybrid-electric demonstrator program.www.ainonline.com Pratt & Whitney Hybrid-electric System To Fly in a Dash 8 in 2024
by Gregory Polek
- July 15, 2021, 2:00 PM
A De Havilland of Canada Dash 8-100 demonstrator powered by a Pratt & Whitney Canada hybrid-electric propulsion system will fly in 2024, according to a new partnership agreement. (Image: Pratt & Whitney)
https://www.facebook.com/sharer/sha...hitney-hybrid-electric-system-fly-dash-8-2024
Pratt & Whitney Canada is partnering with De Havilland of Canada in a program to test hybrid-electric propulsion technology in a Dash 8-100 flight demonstrator, the engine company said Thursday. Expected to undergo ground testing next year and fly in 2024, the demonstrator will include an electric motor and controller from fellow Raytheon Technologies unit Collins Aerospace. The governments of Canada and Quebec have committed to contributing roughly half of the total C$163 million investment the program will require.
“Pratt & Whitney Canada is proud to be a leader toward ever more sustainable aircraft propulsion technologies and be an integral part of Canada’s green recovery plan,” said Pratt & Whitney Canada president Maria Della Posta. “With a long-time commitment to sustainability and as Canada’s top aerospace investor in research & development, having invested C$500M annually, we are driving economic growth, innovation, and workforce expertise to benefit the environment.”
The new hybrid-electric propulsion technology will help optimize performance across the different phases of flight, allowing the demonstrator to target a 30 percent reduction in fuel burn and CO2 emissions compared with a modern regional turboprop.
As part of Canada’s green recovery plan, the government of Canada’s Strategic Innovation Fund is backing the technology demonstrator, while the government of Quebec supports the project through Investissement Quebec and the Ministère de l’Économie et de l'Innovation.
Combining advanced technologies developed by P&WC and Collins, the project serves as a successor to Project 804, launched in 2019 as a joint development program between the two companies.
Pratt & Whitney Outlines Vision for Renewing the B-52
Aug. 5, 2021
The Air Force has set an ambitious goal for the B-52 Stratofortress: Update the aircraft for the modern battlefield so the legendary bomber can continue flying combat missions at least 100 years after its first flight. Central to the Air Force’s plan are new engines, which should slash maintenance and fuel costs while delivering significantly improved mission performance and reliability.
“There’s never been a better time to upgrade the B-52 with a modern commercial engine that will provide huge benefits to both the warfighter and the taxpayer,” said former B-52 pilot, retired Lt. Gen. Michael R. Moeller, who is now Vice President for military engines and integrated customer solutions at Pratt & Whitney.
Emerging weapons systems and technologies, evolving mission requirements, and budgetary necessity make the case for engines that deliver better fuel burn, more electrical power generation, and lower life-cycle costs while reducing environmental impacts such as carbon and noise emissions.
Today’s B-52 is a lot like the one Air Force Maj. Gen. Andrew J. Gebara, the director of strategic plans at the Air Force Global Strike Command, piloted early in his career. But once new engines are on board it will be “a very different B-52 than what I flew as a lieutenant.”
With nearly 70 years of experience in the B-52 world, Pratt & Whitney could yet again have the best solution for powering this aircraft. It’s offering the award-winning PW800, which Moeller said is the right fit, offering best in class fuel burn, maintainability, and will be the most sustainable option on the table. Additionally, the size and weight savings of the PW800 avoids the significant integration risks of larger, heavier engines.
A B-52 powered by eight PW800s would meet the Air Force’s goal to extend the jet’s range by up to 40 percent and increase time on station—or loiter time—in the bargain Moeller said.
The Air Force’s request for proposals (RFP) for the engine replacement program, issued in May 2020, stated a requirement for 608 new engines, which would equip all 76 of the B-52 bombers still in its inventory. The service wants a modern, reliable commercial engine in the growth phase of its life cycle and intends to mount them—as in the past—in pairs, with four engines on each wing. To hold down development costs, Air Force leaders ruled out changing the engine configuration or making any significant change in size. The intent is that these engines will essentially be one-for-one replacements with minimal integration work, and no impact to the aircraft structure.
“The replacement engine must have good physical and performance fit,” said Moeller. “It should provide affordability with low integration risk. It should have life-cycle cost benefits, significant savings in fuel-burn, and operate without scheduled overhauls over the life of the program. Overall, maintenance should be significantly less than the current engine. And the PW800 demonstrated all these capabilities through data-based digital engineering during the Air Force’s integration study.”
One unstated benefit of the PW800 is that it’s in the “sweet spot of its life cycle,” Moeller said. The Air Force will want an engine that is sustained by commercial market volume today and decades into the future. The Service doesn’t want an engine that is nearing its commercial sunset and is unsustainable in the future because the commercial market disappeared. The “sweet spot” is that period when a product is in its growth phase with an active commercial market for decades to come. This ensures spare parts availability with a pool of experienced maintainers working with a global sustainment support structure for the life of the program.
Chris Johnson, Vice President of Fighter and Mobility Programs, said, in addition to being in that “sweet spot,” the PW800 is perfectly matched to the mission. “The PW800 is a combination of the right thrust, the right physical size, and very low weight to provide all the required aircraft performance with exceptionally low fuel consumption,” he said.
Pratt & Whitney’s PW800 engine is a proven commercial product, promising 30 percent less fuel burn and saving some 5,400 pounds of weight per aircraft. Pratt & Whitney
The PW800 will stay on wing for decades longer than the RFP requires, Johnson said, and will meet or exceed every capability requirement. While the engine is almost the same dimensional size as the legacy TF33, the combined weight savings over eight engines is 5,000 pounds. That means less wing stress, improved fuel efficiency, and increased capacity for under-wing payloads.
No other option delivers so much weight savings, Johnson said. “The nearest competitor is over 3,000 pounds heavier than the PW800 [for all eight engines],” Johnson said. The other competitors are as much as 6,000 pounds heavier.
As a modern, commercial engine, “the PW800 is fundamentally designed for long life,” said Paraag Borwankar, associate director for PW800 customer programs at Pratt & Whitney. “This design philosophy means the engine won’t require its first overhaul until well beyond the expected life of the B-52 program.”
The PW800 features large access panels to facilitate inspections and a modular design that supports quick access to swap out line-replaceable units (LRU), ensuring rapid intervention capability for Air Force maintenance crews and high mission-readiness rates.
For those rare cases where more extensive maintenance is necessary, Pratt & Whitney has invested $30 million in its Bridgeport, W.Va., maintenance, repair, and overhaul facility, which is dedicated to working on PW800 engines.
“The thing about this program is that the PW800 just works. It really does,” said Johnson. Not that this was easy or without effort, he added. “We’re integrating an electronically controlled entity into what used to be a hydraulically controlled aircraft,” Johnson explained. It’s complex, but a workable challenge. “The system engineering works. It’s all been pretty seamless.”
The Air Force will rely on the B-52 for decades longer as the stand-off element of a multi-level bomber strategy. In hotly contested airspace, the B-2 Spirit and stealthy F-22 and F-35 fighter aircraft will penetrate air defenses and attack as “stand-in” forces, while B-52s and B-1s, without their radar-evading properties, will be used as “stand-off” forces, firing weapons from a safe distance and benefitting from the increased range and loiter times the PW800 will deliver. B-52s can also serve as nuclear-capable bombers and for close air support of ground combat troops, as was frequently the case in Afghanistan and Iraq.
“We understand the critical role the B-52 plays in defending our country and protecting freedom around the world,” Moeller said. “We’re committed to providing a propulsion solution that keeps the B-52 operationally viable for decades to come. And we look forward to the opportunity to continue this partnership with the USAF to power the B-52 with the PW800.”
FAA order targets PW1500G and PW1900G high-pressure compressors
In a move responding to inflight engine shutdowns, the Federal Aviation Administration is requiring airlines to replace components in the high-pressure compressors (HPC) of Pratt & Whitney PW1500G and PW1900G turbofans.
The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all PW1519G, PW1521G, PW1521G-3, PW1521GA, PW1524G, PW1524G-3, PW1525G, PW1525G-3, PW1919G, PW1921G, PW1922G, PW1923G, and PW1923G-A model turbofan engines. The NPRM published in the Federal Register on June 3, 2021 (86 FR 29707). The NPRM was prompted by reports of cracks in the HPC rotor shaft that resulted in vibration and subsequent IFSDs and UERs. The manufacturer determined that the threads on the HPC rotor shaft were not optimized for load distribution, which resulted in vibration stresses. During one occurrence, oil was released at the high-pressure turbine (HPT) disk bore location. The manufacturer redesigned the HPC front hub and HPC rotor shaft for increased durability and decreased vibration stress. The redesigned HPC front hub is made from nickel to help with corrosion resistance. The threads on the HPC rotor shaft were also redesigned to help distribute the load on the threads and decrease vibration stress. In the NPRM, the FAA proposed to require removal and replacement of the HPC front hub and HPC rotor shaft. The FAA is issuing this AD to address the unsafe condition on these products.Airworthiness Directives; Pratt & Whitney Turbofan Engines
The FAA is adopting a new airworthiness directive (AD) for all Pratt & Whitney PW1500G and PW1900G series turbofan engines. This AD was prompted by reports of cracks in the high-pressure compressor (HPC) rotor shaft that resulted in in-flight shutdowns (IFSDs) and unscheduled engine removals...www.federalregister.gov
Pratt & Whitney And Rolls-Royce Downplay CFM Open-Fan Threat | Aviation Week Network
CFM’s open-fan plan grabbed the headlines, but its dependence on gear development has the attention of Pratt and Rolls.aviationweek.com Pratt & Whitney And Rolls-Royce Downplay CFM Open-Fan Threat
Guy Norris August 31, 2021
Shorter inlets, like this Pratt & Whitney test unit, are under study to further improve ducted-turbofan efficiency.
Credit: Pratt & Whitney
Absent for 20 years, open-rotor engines are back on the power agenda for next-generation single-aisle aircraft. What does that mean for the future of conventional turbofans, geared or otherwise, and how might that technology influence the trajectory of tomorrow’s large-engine designs?
These and other questions follow CFM International’s recent seismic decision to focus on an open-fan demonstrator as the most promising route toward a more sustainable successor to today’s medium-thrust turbofans. Aftershocks from the June announcement are still rumbling through the industry and already appear to have factored into the apparent slowdown of Boeing’s next all-new airliner studies.
The General Electric and Safran joint venture program, called Revolutionary Innovation for Sustainable Engines (RISE), targets a 20% reduction in fuel consumption and carbon dioxide emissions compared with current engines and is squarely aimed at a successor to the current Leap 1 turbofan in the 20,000-35,000-lb.-thrust class. The demonstrator program is expected to culminate in 2024-25 with flight tests of a single-stage, gear-driven fan paired with active stators in a tractor configuration—a design never previously tested at full scale.
Yet the RISE effort, which incorporates planned tests of a rotor more than 12 ft. in diameter, is about far more than just the propulsor. The demonstrator program will also include a suite of disruptive technologies that support CFM’s long-term sustainability goals. Among these technologies are multiple new combustor designs to ensure future compatibility with both sustainable aviation fuels and liquid hydrogen. The program also embraces the integration of motors and starter-generators for hybrid-electric adaptation.
Beyond these features, RISE will also include the test and development of a compact high-pressure core to boost thermodynamic efficiency as well as a recuperating system to preheat combustion air with waste heat from the exhaust. In addition, the demonstrator will incorporate the use of advanced materials such as ceramic matrix composites in the hot section and resin-transfer-molded composite fan blades.
Other than the overall open-fan concept itself, however, most if not all these technology areas are also being tackled in some form or other by competitors Pratt & Whitney and Rolls-Royce. The big “new” area, as CFM’s challengers see it, is the low-pressure turbine-driven gearbox interposed between the booster (compressor) and the rotating fan stage.
“It’s still a geared turbofan [GTF]—they downplay that aspect of it—but you cannot make that configuration without a gear configuration,” says Michael Winter, senior fellow for advanced technology at Pratt & Whitney. “In essence, this really is a full-on affirmation that geared turbofans are the future—full stop.” If the open fan does not prove feasible for various aeromechanical or certification-related reasons, the baseline development would also clearly support an alternate ducted, geared-fan configuration. CFM declined to be interviewed for this story, but speaking for Pratt, Winters says: “That is consistent with our assessment.”
After more than a decade of research in Europe and the U.S. into optimized blade designs for aeroacoustics, noise is no longer considered a showstopper for open rotors. Although acoustic challenges remain, the focus is shifting to the equally significant hurdles of integration, mechanical complexity and certification.
CFM believes integration with conventional tube-and-wing configurations will be easier because the overall diameter of its open-fan design has shrunk. When open rotors were tested and flown in the 1980s, they required fans up to 16 ft. in diameter to match the power of a midthrust engine, compared with a planned diameter of just more than 12 ft. for RISE. Although this represents a significant improvement, it still presents an installation challenge for wing mounting on aircraft such as the current single-aisle generation. The Leap 1A on the Airbus A320neo, which is enclosed in a 8.3-ft.-deep nacelle, has a ground clearance of just over 1.5 ft.
Much of CFM’s RISE technology will be equally applicable to an open-fan or geared engine. Credit: CFM International
Even if an open fan is cantilevered up and forward of the wing, Winters says the turbulent wake of the rotor will mitigate against many of the aerodynamic advantages planned for the efficient high-aspect-ratio wing designs under study for next-generation aircraft. “One way Boeing picked up so much efficiency on the 787 wing was by maintaining laminar flow for much of the front section,” he says.
“If you think about where Boeing wants to go with a truss-braced wing in that same time frame—the company’s ongoing transonic truss-braced wing (TTBW) concept study with NASA—it’s a really long, really thin wing,” Winters says. “And for all intents and purposes, I believe it’s assuming laminar flow.” This aerodynamic advantage, he adds, would likely be lost in the wake downstream of an open fan.
Another major integration hurdle will be protecting the structure from blade loss and subsequent imbalance forces, Winter says. Plans to flight-test the Safran-developed counter-rotating open-rotor test engine—the forerunner to RISE—on an Airbus A340 flying testbed were shelved in 2017 after concerns arose about airframe strengthening and weight gain around the tail to counter potential blade separation events.
Winter says open rotors might represent a more significant installation challenge for advanced configurations such as the TTBW. “That truss is a safety-critical structure, and you’ve got this big whirling mass right next to it with the possibility of losing a blade. So you have to worry about the imbalance loads and the structural mass associated with coping with those,” he adds.
CFM notes, however, that the demonstrator will also pave the way for development of a certified product, various issues for which were considered as early as 2015 in a European Union Aviation Safety Agency (EASA) notice of proposed amendment. “The open-rotor concept is not intended to be certified as a propeller-engine installation,” EASA says. “Due to the complex integration, it is instead intended to be certified as an integrated engine concept.”
Based on current airframe and engine certification requirements, the open-fan propulsion system is likely to meet existing turboprop rules, under which the propeller manufacturer has to demonstrate, by design and tests, that a fan blade will not detach. In addition, the system will also have to meet current requirements on blade pitch control and avoiding overspeed conditions. Blade-off requirements similar to current turbofan regulations will also be a factor.
Rolls-Royce, which has bet its future on the geared, ducted UltraFan family, is also skeptical about the prospects for the broader applicability of the open-fan concept. “The ducted fan is far and away the most versatile, and an entirely necessary, solution,” says Andy Geer, chief engineer of UltraFan product development and technology. “You can come up with open-rotor and maybe open-fan configurations for bespoke short-range small airplane applications, perhaps, but only if those applications can tolerate the installation challenges and the sort of cruise-speed limitations that are likely to go with that kind of architecture.”
The issue becomes even more critical with the increasing scale necessary for higher-power needs. Geer says the flow physics for such a requirement demands that for the same overall thrust, the open-fan engine will have roughly twice the diameter of a ducted fan. “Our view is neither of those compromises would work in a widebody, long-range application. Realistically, they’re completely outclassed by an UltraFan ducted turbofan on [such an] application,” he adds.
“There seems to be a fundamental divide from our perspective,” Geer continues. “From a cruise-speed limitation perspective, unless you’re prepared to push an open-rotor system to very high tip speeds to try to overcome some of the shortfalls of not being ducted, you will gain speed. But as soon as you do that, you’ve got a noise problem.”
As Rolls-Royce prepares to begin ground tests of the first UltraFan demonstrator in early 2022 and Pratt works on a road map of upgrades to the GTF, it appears that neither company plans to change course or alter its development strategy as a result of CFM’s RISE initiative. Yet the two manufacturers are in very different positions: Rolls is years away from debuting the new engine and has yet to secure an application for its UltraFan, while Pratt is building on a bridgehead established with an engine family that first ran in ground tests as far back as 2007.
The UltraFan’s large size is evident in this artist’s concept of an engine on the assembly line. Credit: Rolls-Royce
In the near term, Pratt is preparing to launch an upgrade package for the PW1100G version that will provide the option of additional thrust for heavier weight applications, such as the Airbus A321XLR, while maintaining time on wing. The focus is on delivering additional power and reliability rather than lower fuel burn, Winter says.
“The beauty is that we do have that technology and we could take advantage of it, but we don’t have to,” he adds. “We could change the gear ratio and get a lot more performance, but we chose to optimize on what the customer values. That’s not only efficiency—it’s also time on wing and thrust.”
Down the line, Pratt is evaluating further improvements, including short duct inlets and adapting the PW1000G family for a more electric future. The short duct work, which would help reduce the weight and drag of the nacelle, would build on earlier tests of advanced inlets conducted as part of the FAA’s CLEEN environmental program. Plans to develop the engine into a parallel turboelectric hybrid include adding a motor-starter generator mounted on the engine’s high-pressure spool and a motor generator on the low-pressure spool.
These plans will leverage NASA’s Electrified Powertrain Flight Demonstration project, under which Pratt hopes to play a key role in flight testing a megawatt-class electric-aircraft-propulsion system on its Boeing 747SP flying testbed. The program forms part of NASA’s broader aviation sustainability strategy and aims to mature propulsion systems for thin-haul, regional and single-aisle aircraft that could enter service by 2035.
To accelerate the process and mature powertrain technology to a level ready to enter product development and certification in the late 2020s, NASA intends to use existing or planned industry flying testbeds and is expected to issue contracts later this year.
Guy Norris
Guy is a Senior Editor for Aviation Week, based in Colorado Springs. Before joining Aviation Week in 2007, Guy was with Flight International, first as technical editor based in the U.K. and most recently as U.S. West Coast editor. Before joining Flight, he was London correspondent for Interavia, part of Jane's Information Group.
USAF Chief: New F-35 Engine Development Needed, Even Without Commitment To Buy | Aviation Week Network
The continued research and development for a possible F-35 engine replacement is needed, even without a commitment to replace the current F135 powerplant, so the U.S. Air Force can keep the option open and the technology evolving, the top service general said Sept. 8.aviationweek.com Brian Everstine September 08, 2021
USAF Chief: New F-35 Engine Development Needed, Even Without Commitment To Buy
F135
Credit: USAF
The continued research and development for a possible F-35 engine replacement is needed, even without a commitment to replace the current F135 powerplant, so the U.S. Air Force can keep the option open and the technology evolving, the top service general said Sept. 8.
Chief of Staff Gen. Charles Q. Brown Jr., speaking during a Defense News virtual conference, said eventually there will be a “fork in the road” when the service needs to decide if there will be a second engine for its F-35 fleet, “but the value of actually continuing the research and development is important so we do have options in the future.”
Since 2016, the Air Force Life Cycle Management Center has been conducting the Adaptive Engine Transition Program (AETP) to demonstrate three-stream engines. The competition is between Pratt & Whitney’s XA101 and GE Aviation’s XA100 designs, which could be added to F-35s or the future Next Generation Air Dominance system.
Brown and new Air Force Secretary Frank Kendall have reviewed the ongoing effort and decided “if we stopped the R&D … we basically shut ourselves off from having an option to go forward, and so this is why it’s important for us to continue research and development on this particular capability.”
The House Armed Services Committee (HASC), in its markup of the 2022 defense policy bill approved Sept. 2, calls on the Pentagon to approve the use of the AETP on the F-35A. The bill specifically calls on the Defense Department to outline an acquisition strategy for development, integration, and operational fielding of the new propulsion system on to the Air Force’s F-35A fleet starting in fiscal 2027.
The AETP engine is not a requirement for the F-35 yet, but the Joint Program Office has said it is following the development for possible Joint Strike Fighter use.
Meanwhile, Pratt is also proposing a series of upgrades to its F135 engine to improve fuel efficiency while also bettering thrust.
Kendall, in a recent interview with Air Force Magazine, said the service is following “some technologies that could go into future upgrades that could reduce some of the operational costs, such as fuel, significantly,” but added he was not ready to commit to those.
The same HASC bill also outlines a plan to link the total number of F-35s in the Pentagon’s fleet to sustainment costs, cutting tails from the overall force size if the jets remain expensive to operate. Brown said what Congress is trying to do is in line with Air Force plans.
“We are all committed to the same thing—to make it affordable and to make the sustainment costs more reasonable, and so that is a focus for us,” Brown said. “The language from Congress is really in line with what we’re trying to get done.”
Brian Everstine
Brian Everstine is the Pentagon Editor for Aviation Week, based in Washington, D.C. Before joining Aviation Week in August 2021, he covered the Pentagon for Air Force Magazine. Brian began covering defense aviation in 2011 as a reporter for Military Times.
FAA Orders Service for Some P&W Engines
The federal safety agency issued an airworthiness directive for some Pratt & Whitney PW1100G geared turbofan engines, indicating some high-pressure turbine disks may be at risk of failure.
SEP 09, 2021
The Federal Aviation Administration issued an airworthiness directive requiring airlines to replace some high-pressure turbine (HPT) disks in Pratt & Whitney PW1100G turbofan engines, relating the components to some parts that failed on an International Aero Engines V2500 unit in a 2020 incident.
The PW1000G is a high-bypass geared turbofan engine powering the Airbus A220 and A320neo aircraft, as well as the Embraer E-Jet E2 series. It’s also selected for installation in aircraft produced by Mitsubishi Aircraft Corp. and Russia’s United Aircraft Corp.
“The FAA considers removal of certain HPT first-stage and HPT second-stage disks to be an urgent safety issue,” according to the agency, as reported by FlightGlobal. “These HPT disks have the highest risk of failure and require removal within 30 days… This unsafe condition may result in loss of the airplane.”
Pratt & Whitney produces the turbine disks as part of its role in the IAE consortium. Disks installed in Pratt’s PW1100G units are made from a similar material.
The 2020 incident involved an “uncontained HPT first-stage disk failure that resulted in high-energy debris penetrating the engine cowling,” according to FAA and quoted in the online report. “Pratt & Whitney determined that the failure… was due to an undetected subsurface material defect in an HPT disk.”
Reportedly, Pratt & Whitney reviewed all of its own and IAE models that incorporate the similar parts, identifying 55 PW1100G engines installed in aircraft worldwide requiring the replacement disks.
The FAA’s airworthiness directive requires U.S. airlines to replace the affected parts within 30 days.
Pratt Testing XA101 Adaptive Engine, Has Two Offerings for F-35 Propulsion
Oct. 1, 2021 | By John A. Tirpak
Pratt & Whitney is testing its new XA101 Adaptive Engine Transition Program powerplant, and expects to conclude testing its two examples by the end of next year, company military engines division president Matthew Bromberg revealed in an interview. He expects that two-thirds of the technology developed from AETP could find its way into earlier engines now flying with the Air Force.
The company is “thrilled” to have two options available for the Air Force and F-35 partners to choose from for an upgrade to the fighter’s propulsion system, Bromberg said. GE Aviation has developed the XA100 AETP engine as a competitor to Pratt’s version.
Testing of “our first new fighter engine in 30 years … was successful,” Bromberg said. The first XA101 and its twin will shuttle back and forth between Pratt’s facilities and the Air Force’s Arnold Engineering Center in Tullahoma, Tenn., for the next year or so, generating more data. The Air Force and F-35 Joint Program Office will use the data to help decide whether the F-35 should get an all-new powerplant—one of the AETP engines—or take Pratt up on its offer of an enhanced version of the F135 engine already in the F-35 fighter.
Pratt succeeded in achieving the AETP’s goals, which were to obtain 10 percent improvement in thrust and 25 percent improvements in both fuel efficiency and thermal management, Bromberg said. “We know we can do that,” he said.
“Job Two” is to determine whether the engine will last, and further testing will assess Pratt’s use of new materials, created both in traditional ways and through additive methods, to demonstrate the powerplant can go “years between scheduled maintenance events.” Continued testing will assess how those “structures and materials are performing,” he said.
However, “we’re not going to test everything you would do in a full-blown” engine development program, he said. “We’re going to test items we want to risk-reduce; we want to make sure we understand how the engine will perform at this point in the program.”
The intent of AETP was “always … to create a sixth-generation propulsion system and an adaptive engine,” Bromberg said. “Now the debate is focusing on modernizing the Joint Strike Fighter. And we think it’s a good time to have that debate.”
Bromberg said he expects that up to “70 percent … of the technologies we’ve developed in the adaptive architecture … will go into other engines as derivative technologies.” This will not include the third-stream adaptive technology itself, but the materials, accessories, and “other mechanical systems” that go with the engine, Bromberg said. “It’s a big part of how you drive efficiency of the engine and control the entire cycle.”
He cautioned that these technologies would need to “buy their way in” to upgrades to the F100 and F119, used on the F-15 and F-16, and F-22, respectively, but “two-thirds-ish could be leveraged” for those earlier systems, and “obviously, every future engine that we design will leverage that entire technology suite.”
The AETP, as sixth-generation engine technology, is “the future of Air Force propulsion,” Bromberg said. It has been “an incredibly successful program” in advancing the state of the art in engine technology.
The AETP achieves better thrust while also improving fuel efficiency by adding a third air stream, which can also be used for cooling. Air Force and JPO leaders have said they will need more thrust and cooling in the F-35 in order to get full capability out of the Block 4 version of the fighter, set to start coming off the production line in 2023.
The House Armed Services Committee, in its markup of the 2022 National Defense Authorization Act, directed the JPO to develop a plan for mating AETP engines to the F-35 fighter by 2027.
Neither Pratt’s XA101 nor GE’s XA100 will fit in the F-35B short takeoff and vertical landing version, however. Bromberg said the reason has to do with the three-bearing swivel nozzle employed by the F-35B being “incompatible” with the third-stream architecture. It might be possible to use the AETP engine in the Navy’s F-35C carrier version, Bromberg said, if the arresting hook system could be moved to accommodate it. He said Pratt has had discussions with Lockheed Martin to that effect.
“We could modify it to fit around some of the unique elements of the adaptive engine, but that’s work to be done,” he said.
What happens now is “up to the services,” Bromberg said. “There’s a recognition that we need to modernize the propulsion system in the Joint Strike Fighter,” and Pratt is “unique” in having two solutions to that requirement. But each has its “advantages and disadvantages.” An upgraded F135 wouldn’t have all the advantages of adaptive technology, but using the AETP would require establishing multiple engine support lines for the fighter.
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