4
TF33 Series Powered Aircraft

INTRODUCTION

The Air Force currently owns approximately 2,300 TF33 engines of various models that it uses on seven weapons systems, mainly the KC-135, E-3 Advanced Warning and Control Systems (AWACS), B-52, and E-8 (Joint Surveillance and Target Attack Radar System (JSTARS)) aircraft (Parker, 2006). Designed in the 1950s and manufactured in the 1960s and 1970s, the TF33 is one of the oldest engine families in the Air Force inventory. Given their age and number, TF33-powered aircraft have been the subject of numerous re-engining studies over the years (at least nine studies since 1984), one executed reengining program (the conversion of most earlier KC-135s to the KC-135R model), and one in-progress program (re-engining of the E-8).

The re-engining of different TF33-equipped platforms is discussed in detail in the following subsections. However, there are four considerations that pertain to more than one platform and that may distinguish a present-day re-engining effort from past efforts. The first common consideration is that the maintenance interval of modern engines exceeds the life of these old airframes. Specifically, (1) the very long on-wing lives of the best modern commercial transport engines (7 years or more on wing, which amounts to 10,000 hr or more compared to the TF33’s 1,500-2,500 hr), (2) the low annual utilization of most TF33-powered platforms (only 10-20 percent that of a commercial operator), and (3) the plans in 2006 for the inventory life of these platforms all combine to suggest that properly selected new engines would not be expected to come off the wing for an overhaul during the remaining life of the platform. Since major overhauls account for most of the maintenance cost associated with engine ownership, the true cost to the Air Force of these modern engines may be less than their cost based on a standard cost-of-ownership estimate, which spreads the overall maintenance cost over the total operating hours.

A second new consideration is the dramatic and rapid increase in the Air Force’s overhaul cost for TF33 engines. Depot overhaul of a TF33 is estimated to have cost $257,000 in FY96. Since FY03, the TF33-PW-102 depot overhaul cost has increased by 300 percent, to $1.25 million per engine in FY06. This cost growth greatly surpassed the earlier 2 percent per year projections. The causes of this escalation were not made clear to the committee, but it notes that the commercial version of the TF33, the JT3D, which was once one of the largest engine fleets, has largely gone out of service since it does



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Improving the Efficiency of Engines for Large Nonfighter Aircraft 4 TF33 Series Powered Aircraft INTRODUCTION The Air Force currently owns approximately 2,300 TF33 engines of various models that it uses on seven weapons systems, mainly the KC-135, E-3 Advanced Warning and Control Systems (AWACS), B-52, and E-8 (Joint Surveillance and Target Attack Radar System (JSTARS)) aircraft (Parker, 2006). Designed in the 1950s and manufactured in the 1960s and 1970s, the TF33 is one of the oldest engine families in the Air Force inventory. Given their age and number, TF33-powered aircraft have been the subject of numerous re-engining studies over the years (at least nine studies since 1984), one executed reengining program (the conversion of most earlier KC-135s to the KC-135R model), and one in-progress program (re-engining of the E-8). The re-engining of different TF33-equipped platforms is discussed in detail in the following subsections. However, there are four considerations that pertain to more than one platform and that may distinguish a present-day re-engining effort from past efforts. The first common consideration is that the maintenance interval of modern engines exceeds the life of these old airframes. Specifically, (1) the very long on-wing lives of the best modern commercial transport engines (7 years or more on wing, which amounts to 10,000 hr or more compared to the TF33’s 1,500-2,500 hr), (2) the low annual utilization of most TF33-powered platforms (only 10-20 percent that of a commercial operator), and (3) the plans in 2006 for the inventory life of these platforms all combine to suggest that properly selected new engines would not be expected to come off the wing for an overhaul during the remaining life of the platform. Since major overhauls account for most of the maintenance cost associated with engine ownership, the true cost to the Air Force of these modern engines may be less than their cost based on a standard cost-of-ownership estimate, which spreads the overall maintenance cost over the total operating hours. A second new consideration is the dramatic and rapid increase in the Air Force’s overhaul cost for TF33 engines. Depot overhaul of a TF33 is estimated to have cost $257,000 in FY96. Since FY03, the TF33-PW-102 depot overhaul cost has increased by 300 percent, to $1.25 million per engine in FY06. This cost growth greatly surpassed the earlier 2 percent per year projections. The causes of this escalation were not made clear to the committee, but it notes that the commercial version of the TF33, the JT3D, which was once one of the largest engine fleets, has largely gone out of service since it does

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Improving the Efficiency of Engines for Large Nonfighter Aircraft not meet environmental regulations of most of the developed world and is much less fuel efficient than current engines. The third consideration is that with the exception of the B-52H, all of the other TF33-powered weapons systems are KC-135/B-707 variants or derivatives. Given that the KC-135Rs have been reengined and the E-8 JSTARS re-engining is now in progress, a significant fraction of the nonrecurring engineering costs may be shared among platforms rather than duplicated. The fourth consideration is that the Air Force maintains a significant engineering and overhaul capability to support its fleet of 2,300 relatively high maintenance TF33 engines. So long as a significant number of TF33s remain in the inventory, the Air Force must retain some overhaul capability. Should all of the TF33s be retired, however, then the $800 million inventory can be disposed of and the more than 188 personnel and 82,000 sq ft of support real estate can be suitably redeployed for other Air Force needs. For these nonnegligible savings to be fully realized, all TF33 engines have to be removed from the inventory. If, for example, all of the KC-135/B-707 variants are re-engined, this may strengthen the case for the B-52. Taken together, these considerations strongly suggest that TF33-powered aircraft should be considered as a group rather than subjected to the traditional approach—i.e., airframe by airframe studies. In this case, the whole of the savings from re-engining all TF33 aircraft may considerably exceed the sum of re-engining the individual platform types. The following sections discuss re-engining for each of the current platform types. E-8 JSTARS WEAPONS SYSTEMS Throughout the development history of JSTARS a number of engine options have been studied. By re-engining the JSTARS E-8C aircraft, the government will benefit from substantial reductions in fuel burn and other costs of ownership, while enhancing all operational requirements with a new installation that more than meets all environmental requirements.1 However, in each case the conclusions were similar to those for the other platforms that had conducted business case analyses on payback—i.e., the payback period is too long to recoup the significant upfront nonrecurring engineering (NRE) and acquisition costs. From its inception the JSTARS platform was structured around Boeing 707 aircraft that were being operated by the Air Force, foreign governments, and commercial carriers. The program utilized Boeing 707-320C (Air Force designation C-18) series aircraft obtained in the commercial marketplace as they were being phased out by the major and secondary commercial carriers. The 707-320C aircraft had received its Federal Aviation Administration (FAA) certification in April 1963. At the time the aircraft were procured from the used market, there were only limited engine options offered for them. The original Boeing 707-320 aircraft design goals were to provide an aircraft whose aeronautical performance was optimized for long-range flight, making it the first truly intercontinental jet aircraft. The Boeing 707 had adequate thrust to meet the needs of a commercial operator carrying large loads between distant points on the globe. The engines available for the aircraft back in the 1960s had 18,000 lb thrust in the JT3D-3 or -3B commercial configuration or 19,000 lb thrust in the -7 variant. It should be noted that the wing structure of a Boeing 707-320 series aircraft is nearly identical to the wing structure of an AWACS that is currently operating with a 21,000 lb thrust engine. However, the long radar aperture along the bottom fuselage of the aircraft results in problems with aircraft lateral stability, which is aggravated by increased 1 On January 18, 2007, the Air Force announced that it had selected the Pratt & Whitney (P&W) JT8D-219 engine to re-engine the entire Joint STARS fleet (Northrop Grumman, 2007).

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Improving the Efficiency of Engines for Large Nonfighter Aircraft thrust. Any re-engine program for the JSTARS aircraft will have to address the issue of improving the aircraft’s lateral stability to meet military standards. In the early 1990s, an early deployment of the two full-scale-development JSTARS aircraft during Operation Desert Storm demonstrated the operational effectiveness of the weapons system; however, a number of areas were identified that would need significant improvements in aeronautical performance to meet the original Operation Desert Storm requirements and to gain maximum utility from the E-8 system. The main areas identified were these: Reduced takeoff distances at maximum weight under military flight rules. Reduced time to achieve the JSTARS initial surveillance altitude. Larger engine oil tanks to extend aircraft time on station. Greater unrefueled range. Improved hot-day takeoff performance coupled with shorter runway lengths. Improved maneuvering capabilities at surveillance altitude. Reduced engine maintenance time between flight sorties. The lessons learned from the Desert Storm deployment were assessed not just for the JSTARS surveillance role but also for related aircraft performance. A follow-on full-scale development (FOFSD) was proposed using the YE-8B aircraft, which was a derivative of the current Boeing/U.S. Navy E-6 aircraft powered with CFM56-2 engines. This engine develops 24,000 lb thrust and would have resolved a number of performance improvements sought by the operator. A primary consideration for any re-engining program for the JSTARS aircraft is the effect on radar performance. Unobstructed operation of the radar and improving the performance of the radar by increasing the operating altitude of the aircraft have been identified as two key considerations. When affordability and availability of the Boeing YE-8B (new 707) became an issue owing to the cost of keeping the B 707 production line open, the program was rebaselined to again utilize a used 707-320 series platform. The ensuing FOFSD program used the same aircraft performance requirements as the FSD system. During the development phase for the FOFSD, an effort was made to resolve some of the aircraft’s performance issues by offering to select used aircraft that were powered with the P&W JT3D-7 engine variant, which provided 5.5 percent more thrust than the FSD system. In addition, a study was done to determine if lower thrust JT3D-3B engines on an aircraft acquired for the program could be converted to the JT3D-7 configuration during planned engine overhaul. It was determined that P&W engine hardware kits were indeed available for conversion and that such conversion was a common practice in the commercial marketplace. However, neither the engine conversion nor the acquisition of aircraft with the JT3D-7 engines for the JSTARS production program turned out to be an option owing to the high cost of hardware conversion at the time of the planned overhaul. Achieving commonality with other Air Force aircraft, e.g., KC-135E tankers using the same JT3D-3B engine, was judged to be a more economical approach than an upgrade or replacement. In addition, the related Air Force engine overhaul facilities supporting TF33 class engines were looked at. To understand if there were any engine options available in the marketplace that would improve the aeronautical performance of JSTARS and other of its aircraft, the Air Force commissioned a re-engining roadmap integrated product team (IPT) in 1997. The goal of this endeavor was to analyze the then state-of-the-art engines that were powering the commercial fleets and determine if there was a cost-effective re-engining option that satisfied the Air Force ground rules. Each of the engine manufacturers—P&W, GE/Snecma (CFM International2), and Bavarian Motor Works/Rolls-Royce (BMW/RR)—had engines 2 CFM International is a joint venture between GE Aviation of the United States and Snecma of France.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft that could meet the operational needs of the Air Force. The engines that were studied were the BMW/RR BR-715, which was under development at the time of the 1997 study; the GE/Snecma CFM56-2 and, to a lesser extent, their CFM56-3; and the P&W JT8D-219. Figure 4-1 shows an E-8 JSTARS aircraft with TF33 engines next to an AWACS powered by CFM56-2 engines. As shown in Figure 4-1, modern GE, P&W, and RR engines for large aircraft are larger than the original TF33 engine (and they are heavier as well). The increase in engine weight is offset by the greater reliability, higher thrust, increased fuel efficiencies, and higher operating altitudes. Any of the three engine options could have provided substantial operational benefits to JSTARS while meeting today’s noise and environmental requirements and reducing engine maintenance and fuel costs. As noted above, the re-engining option was not incorporated in the JSTARS program at that time due to the high NRE costs of developing the re-engining package and the total acquisition cost of re-engining the fleet. Subsequent to the IPT’s re-engining roadmap study, several more studies were initiated looking at various options such as utilizing higher thrust TF33 engines from the C-141 fleet being retired. The TF33 engine offered a number but not all of the performance improvements sought by the user. The engine is basically of the same vintage as the P&W JT3D-3B and can be made to meet International Civil Aviation Organization (ICAO) Stage III noise standards with the addition of a hush kit, but it cannot be made to meet Stage III emissions standards. Also, being an older technology engine it did not offer the reduced fuel burn, lower cost of ownership, and greater reliability achieved with today’s engines. Today, the JSTARS aircraft is still flying with the TF33-3B engines that were installed when the aircraft were first acquired by the Air Force. These older engines are resulting in low mission-capable rates, the highest in-flight engine shutdown rate of all nonfighter aircraft, and a spiraling increase in engine depot costs. Demand by theater commanders for the aircraft continues to grow, raising serious concerns about flight safety and reliability (see Figures 4-2 and 4-3 for E-8 JSTARS data). The engine shutdown rate for the TF33 is 70 times that of current engines, which indicates to this committee the urgent need to re-engine this aircraft. FIGURE 4-1 E-8 JSTARS with TF33-102C engines and Royal Air Force AWACS with CFM56-2 engines. SOURCE: Alan van Weele.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft FIGURE 4-2 E-8 average flying hours per aircraft each year. SOURCE: Foringer (2006). Currently all the JSTARS engines are being upgraded from the JT3D-3B configuration to the -7 configuration during their planned overhaul. This upgrade will provide a slight improvement in aeronautical performance but will not significantly reduce the cost of ownership of JSTARS aircraft. It is considered a stopgap measure until a viable re-engining option is introduced. The costs of maintaining the current engine, cowl set, and thrust reversers will still be present for the JT3D-7 engine until a complete new installation has been incorporated into the JSTARS baseline. Depot costs for either the -3B or the -7 engine will continue to increase at a rate that is unsustainable. Since FY03 the depot cost for TF33 engine overhaul has increased by 300 percent, to $1.25 million per engine. With the increasing tempo FIGURE 4-3 JT3D in-flight shutdowns. RFI, ready for issue. SOURCE: O’Grady (2006).

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Improving the Efficiency of Engines for Large Nonfighter Aircraft of operation and age of the engine, the in-flight shutdown rate and depot cost are expected to increase even faster (Figure 4-4). There are serious issues other than fuel efficiency that need to be considered before deciding on replacement of the TF33 engine on the E-8 through a re-engine program by modern, highly reliable, fuel-efficient engines. E-3 AWACS PLATFORM The AWACS aircraft can also be traced to the commercial Boeing 707-320B advanced passenger model that was produced at the end of the Boeing 707 production run. These aircraft had some of the same structural characteristics as the B 707-320C combi/cargo variation that was used as the input aircraft for the JSTARS program. The core input aircraft for AWACS was extensively modified, the distinctive radome was mounted on top of the aft fuselage, and extensive changes were made to the aircraft subsystem to support the mission systems and associated equipment. A new engine was needed to handle the greater drag of the AWACS relative to that of the commercially powered P&W variants. The existing engines had a maximum thrust rating of 19,000 lb, while the new P&W engines were to be an FAA-certified model having 21,000 lb thrust. Concurrently with the AWACS program, Boeing was planning for a new B 707 model known as the B 707-700, which was to be powered with CFM56–2 engines. One aircraft, the last commercially built B 707, was modified for a flight test program by installing 24,000-lb-thrust CFM engines and operated for 2 years gathering performance test data for the planned new model. At the completion of the test program, the aircraft was returned to its original power plant configuration with P&W JT3D-7 engines, modified to an aerial tanker configuration, and sold to the Moroccan Air Force. The B 707-700 program was never launched, but the data provided the foundation for the KC-135R re-engining program and the re-engined AWACS aircraft for the Saudi, French, and British governments. FIGURE 4-4 Cost avoidance potential for the TF33. SOURCE: O’Grady (2006).

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Improving the Efficiency of Engines for Large Nonfighter Aircraft The E-3 AWACS family of aircraft has been built with two basic engine configurations. The U.S. (Figure 4-5) and North Atlantic Treaty Organization (NATO) aircraft (Figure 4-6) are powered by the P&W TF33-100 engines, while the British, French, and Saudi governments have aircraft (Figure 4-7) powered by CFM56-2 engines. All of these configurations were part of the aircraft as it went through the production line. Putting new engines on the U.S. and NATO aircraft would now encompass an aircraft modification program with some NRE required. However, a lot of NRE that normally would have been necessary for a re-engine program will not be required since multiple aircraft/engine candidates are available. Each aircraft re-engine program and mission has unique requirements that drive NRE whether or not a specific engine has been integrated onto the platform, and the AWACS aircraft is no different. Although there will be NRE for an Air Force re-engining program, it will be substantially less complicated than it would have been if there were not B 707-320 aircraft flying with engines more modern than the TF33-class engine. When considering a re-engining program for the U.S. AWACS, a number of choices present themselves. The most likely candidate list for a re-engining program includes the GE CFM56-2/-3/-5/-7, P&W JT8D-219, and RR BR-715 engines, as well as several others. All of these candidate engines will require NRE to handle the dual generator requirement of the AWACS aircraft. The dual generator requirement is a good example of the uniqueness of any re-engining program. Even though an engine has been integrated into a similar category/class of aircraft, it is the unique military mission and requirements that drive additional NRE. The complexity and benefits of the modification of an aircraft are related more to the unique requirements than to the engine choice. The committee also has seen the natural tendency to group modifications together to take advantage of the downtime that a re-engining program demands. Other modifications that eliminate line replaceable units like analog gauges, older autopilots, and flight director systems or that add capability like digital displays, data links, and improved navigation systems seem to find their way into the re-engining program. As it has done FIGURE 4-5 U.S. E3-C AWACS powered by P&W TF33-100 engines. SOURCE: Air Force.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft FIGURE 4-6 NATO E3-A AWACS powered by P&W TF33-100 engines. SOURCE: NATO. FIGURE 4-7 United Kingdom E3-D powered by GE/CFMI CFM56-2 engines. SOURCE: Alan van Weele.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft with other platforms having the TF33 engine, the Air Force has studied the potential for re-engining the AWACS aircraft. All of the studies concluded that although there are multiple candidate engines and NRE for this specific platform would be less complicated than most NRE for other platforms, the business cases based on reduced engine maintenance and fuel costs do not justify a re-engining program given the utilization rate and service life. However, this committee believes the Air Force should take another look at a re-engine program for the AWACS aircraft based on eliminating the TF33 engine entirely. An example of successful re-engining is that of the KC-135R aircraft, which gave it the operational capability and fuel efficiency needed to support our nation’s growing security needs. The U.S. AWACS aircraft are excellent candidates for re-engining since the NRE and risk are minimal and significant improvements in fuel efficiency, operational capability, and engine reliability, together with reduced total weapon system support costs, could be achieved. B-52 AIRCRAFT While the design of the B-52 bomber dates back to the early 1950s, only B-52H models with TF33 turbofans are still in inventory (earlier models were equipped with older J57 turbojet engines). The 76 aircraft currently in inventory are supported by over 600 TF33-PW-103 engines. The B-52H is currently expected to stay in inventory until 2045. There have been at least seven studies of re-engining the B-52 since 1997. These studies differed in their assumptions but considered several different choices of engines as well as both direct purchase and various leasing arrangements. Financing is discussed elsewhere in this report. The studies reached similar conclusions: Newer commercially available engines offer significant fuel savings; a re-engining program would be very expensive, more than can be justified by fuel savings alone; and significant improvements in operational employment and performance can be expected. However, all these previous life-cycle studies significantly underestimated the increase in costs for both TF33 repair at the depot and fuel. The cost per engine overhaul grew from $286,000 in FY99 to $1.025 million in FY06. The B-52 is unique in that is uses eight engines, which were the largest jet engines available at the time. Since then, engine thrust capability has grown severalfold, so that it is possible to replace each pair of engines with a single larger turbofan with the same or greater thrust. There are many technically viable candidate engines available for re-engining, all offering fuel savings of 25 percent or more. These range from variants of engines now out of production (such as the JT8D and CFM56-2, for which production would be restarted), to engines currently in production for commercial or military uses (the PW F117—PW2040 is the commercial version—the RR RB211-535, and the GE CF34-10), to engines that exist only in concept (a PW F119 core powering a higher bypass fan). These engines differ in many respects, including physical size and weight, thrust at takeoff and at cruise, net installed drag, nacelle modifications needed, as well installation and interface details. Most of these engines require the purchase of all new nacelles as well as engines. Replacing each two-engine pair with one larger engine requires the purchase of all new nacelles and pylons (which can be as expensive as the engines) as well as resolving engine-out recovery issues (since an engine failure of a four-engine aircraft results in a 25 percent loss of thrust rather than a 12.5 percent loss for an eight-engine aircraft). Additional engineering concerns (see Figure 4-8) include cockpit and control interfaces as well as the quickstart capability needed if the B-52 is to continue with its nuclear single integrated operational plan. Also, because unlike the other TF33-powered Air Force platforms, the B-52 carries and releases weapons, safe weapons separation must be ensured, especially for wing-pylon-carried munitions.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft FIGURE 4-8 Technical considerations in B-52 re-engining. SOURCE: Garcia (2006). The GE CF34-10 is a new commercial engine suitable for B-52 re-engining that was not considered in the re-engining studies referred to above. It is close to the same diameter as the TF33, so that an eight-engine CF34-10 installation would be very similar to that on the current aircraft, possibly obviating many of the engine-out and stores-release concerns engendered when replacing eight engines with four larger ones. The committee did not review either an engineering analysis or a business case for this option. Like the other TF33-powered Air Force platforms, re-engining the B-52 would reduce both fuel and maintenance costs as well as provide operational benefits such as access to shorter runways, higher takeoff weights at high ambient temperatures, and longer range and endurance. Reduced dependence on foreign oil, improved operational capabilities, and enhanced Global Power projection are important considerations that should be taken into account in the decision to proceed or not proceed with a re-engining program for the B-52. This committee believes these less tangible benefits, considered in conjunction with the improvements in fuel burn and maintenance costs, swing the argument for proceeding with a re-engining program. Previous studies showed that fuel savings of 15-20 percent could be realized for the B-52 alone, increasing to 38 percent for a mission when tanker fuel is also a factor. Also, unrefueled mission radius can be increased by 45 percent. Maintenance costs for the B-52 engines have grown much, much faster

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Improving the Efficiency of Engines for Large Nonfighter Aircraft than anticipated, by severalfold since the last study (DSB, 2004). Also, there are now more engine options available, perhaps reducing the NRE and certification costs, and fuel is much more expensive, making the case for re-engining even stronger. KC-135 AIRCRAFT The Boeing KC-135 Stratotanker has been the mainstay of the Air Force aerial refueling fleet for the past 50 years. During that time, the aircraft have provided cargo capability and in-flight refueling for transport, bomber, reconnaissance, and fighter aircraft of the Air Force, the Navy, the Marine Corps, and the militaries of allied nations. The original Boeing KC-135A Stratotanker utilized Pratt & Whitney J57-P-59W engines augmented with water injection at takeoff. In service, the capabilities of these engines imposed limitations on the takeoff maximum gross weight of the aircraft, especially on hot days. In the mid-1970s, Boeing produced a prototype 707 aircraft with high-bypass CFM56 engines, the 707-700. This configuration was intended to provide commercial customers with higher thrust, improved fuel economy, lower operating and maintenance costs, and much quieter operation. Full-scale production of this model was not pursued by Boeing, however, and the program was canceled. The Air Force expressed an interest in the CFM56 engine for its KC-135 fleet, and after reviewing the design and performance, elected to award Boeing a contract in 1979 to engine the KC-135A with the CFM56-class engine (military designation F108-CF-100 and commercial designation CFM56-2B-1). KC-135 aircraft configured with new CFM56-2B-1 engines were redesignated KC-135R. Figure 4-9 depicts the various modifications made to the KC-135A that accommodated the CFM56 engine and allowed increasing the maximum gross weight of the aircraft from 301,000 lb to 322,500 lb. Although no modification was required for putting on the new CFM56 engines, the landing gear and nose wheel steering were modified, allowing an increased gross weight, which in turn allowed the Air Force to utilize the full capacity of the integral fuel tanks. These airplanes have been re-engineered with the CFM56-2 engine models that provide better takeoff performance, range, and fuel burn than the J57-powered KC-135A. The A to R benefits are as follows: More fuel efficient CFM56 is 31 percent more fuel efficient than the J57. Cheaper to maintain Significantly reduced unscheduled maintenance, Fewer depot maintenance hours, and F108 (military designation for the CFM56-2) features in common with the CFM56-2 allow it to take advantage of the large commercial usage. Better aircraft performance Reduced aircraft takeoff roll: 38 percent, Increased thrust: 41 percent, Increased fuel offload: 15 percent, Noise reduction: 95 percent, and Reduced emissions: 97th percentile. A KC-135 aircraft equipped with CFM56-2B-1 engines shows significant improvements: 60 percent increase in thrust from the KC-135A baseline,

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Improving the Efficiency of Engines for Large Nonfighter Aircraft FIGURE 4-9 The KC-135 A to R. SOURCE: Shuppert (2006). 27 percent improvement in fuel efficiency, 98 percent reduction in noise area impacted during takeoffs, and 20 percent reduction in critical field length at increased takeoff weight. The last KC-135A tanker modification with CFM56-2B-1 engines was completed in 1995. In 1981 the Air National Guard and the Air Force Reserve began their own program to re-engine 161 KC-135A aircraft with TF33-PW-102 engines and struts procured from retiring commercial 707 aircraft. These aircraft received the designation KC-135E. Although not as significant as the improvements of the KC-135R, the KC-135E did provide some advantages over the KC-135A: 30 percent increase in thrust, 14 percent decrease in fuel consumption, and 85 percent reduction in noise area impacted during takeoffs. After completion of the program to re-engine its KC-135A aircraft, the Air Force started a program to re-engine its KC-135E tankers with the CFM56-2B-1. For budgetary and other reasons, however, 114 of the tankers have not been so modified. From 1981 to 2006, Boeing modified a total of 470 KC and RC-135 aircraft with CFM56 engines. After the delivery of the last RC-135 to receive CFM56-2B-1 engines in May 2006, the re-engine production line was shut down. The Air Force has contracted with Boeing to maintain the capability

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Improving the Efficiency of Engines for Large Nonfighter Aircraft to restart the CFM56-2B-1 re-engine line if DoD and the Air Force elect to re-engine part or all of the remaining KC-135E aircraft. Several rough order-of-magnitude estimates of the costs of restarting the re-engining line have been completed by Boeing and GE. The latest, sent to this committee in June 2006, estimated start-up costs of approximately $25 million and recurring costs of $33 million per aircraft. The KC-135R does offer significant improvements in reliability, maintenance, and operational performance over the KC-135E with TF33-PW102 engines: 18 percent reduction in specific fuel consumption, 20 percent improvement in critical field length, 25 percent improvement in time to climb, and 20 percent improvement in fuel offload. A number of upgrades had been and are still being introduced in commercial CFM56 engines. Examples are 3D and tech insertion programs. They result in fuel savings and increased reliability, and the Air Force should consider them for upgrading the F108 fleet. TF33-PW102 depot maintenance costs have been increasing rapidly, with the depot cost per engine in FY06 equaling $1.25 million. The Air National Guard expects that depot cost will continue to increase less than 3 percent each year. Since FY03, the depot maintenance cost for the TF33-PW102 engine has increased 300 percent. The Air Force has stated its intention to retire the remaining 114 aircraft equipped with TF33 engines by the end of FY08. If indeed it decides to do this it makes no economic sense to restart the re-engining program. As noted above, the Air Force may realize significant savings and efficiencies by thinking of its engine assets in terms of engine model type rather than individual weapon system or platform. The case for improving operational efficiencies and investment strategies might be strengthened by extending it to include the common engines used by the other services. This view of volume effects on strategic acquisition and operations could prevail insofar as the Air Force has been designated the lead service on aircraft engines. This should provide the mechanism for a DoD-wide approach to fuel savings, extending from the focused intraservice R&D to produce new fuel-efficient propulsion systems to re-engining or upgrades of the fleets. One nonfighter engine used by more than one service is the T56, which is used by both the Air Force and the Navy in the C-130 fleets. The T406 engine is used in the V-22 in multiple services. Finding 4-1. The TF33 engine population is one of the largest and one of the oldest in the Air Force inventory and powers aircraft having some of the most critical missions. Finding 4-2. The maintenance costs on all segments of the TF33 population have escalated considerably over the past 7 years, outpacing the inflation rate and the budgeted allocations. Finding 4-3. The in-flight shutdown rate for the engine is one of the highest in the Air Force fleet, and readiness is negatively impacted by high removal rates. Finding 4-4. TF33 engines, which were once ubiquitous in the civil fleet, are no longer in service in developed nations because they flout environmental restrictions. Finding 4-5. The TF33 engine is deployed in several different model configurations on the various platforms and displays a range of thrust and installation features.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft Finding 4-6. The weapon systems themselves have varying demands in terms of compressor bleed requirements, power extraction, external weapon location and release interference, and radar field of view. Finding 4-7. All of the TF33-powered aircraft have been the subject of extensive re-engining studies, and in several cases either flight demonstration programs or successful operational models have been completed. This includes the E-8 re-engining activity currently in progress. Finding 4-8. Several candidate engines have attributes that could contribute to significant fuel savings and reduced maintenance costs. Finding 4-9. The fuel saving from re-engining with modern engines will not, in and of itself, justify the cost of the program owing to the relatively low utilization rate, the high cost of fuel, the small fleets, and the short planned service life. Conclusion 4-1. The removal of the TF33 engine from the inventory and its replacement with modern, long-overhaul-interval engines will significantly improve operating cost and readiness and save fuel. Conclusion 4-2. The differing requirements of the various weapon platforms may mean that each platform needs a different engine. Conclusion 4-3. The operational experience with re-engined versions of some of the systems makes such re-engining very low risk and highly predictable in terms of nonrecurring and operational costs. Recommendation 4-1. The Air Force should approach re-engining of the aircraft powered by the various models of the TF33 engine on a holistic basis with the goal of removing the engine(s) from the inventory. Recommendation 4-2. The Air Force should immediately conduct for each TF33-engined weapon system an internal review and competitive re-engining study that looks at fuel savings, operational capabilities, and maintenance costs as figures of merit in order to select the best option. Recommendation 4-3. The Air Force should give strong consideration to employing commercial support practices and contractual arrangements to minimize infrastructure and staffing costs. REFERENCES Published DSB (Defense Science Board). 2004. Defense Science Board Task Force on B-52H Re-Engining. June. Available online at http://www.acq.osd.mil/dsb/reports/2004-06-b52h_re-engining.pdf. Last accessed on January 16, 2007. Northrop Grumman. 2007. Joint STARS Engine Replacement Program Takes Major Step Forward. Press Release SVP07-02, January 18.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft Unpublished Mark Amos, Head, New Engines Division, Agile Combat Support Systems Wing, “United States Air Force large aircraft inventory,” Presentation to the committee on April 26, 2006. Mark Foringer, Division Chief, A9RI, “Inputs to AFSB,” Background information provided to the committee on June 23, 2006. Rafael Garcia, B-52 Systems Program Office, Tinker Air Force Base, “B-52 re-engine study,” Presentation to the committee on April 26, 2006. Michael O’Grady, Joint STARS Re-Engining Program Manager, “Joint STARS re-engining,” Presentation to the committee on May 24, 2006. Otis Parker, TF33 Logistics Lead, 448th Combat Sustainment Wing, “TF33 engine data summary,” Presentation to the committee on April 26, 2006. James Shuppert, Director of Sales, GE Tanker/Transport/ISR Engines, “General Electric presentation,” Presentation to the committee on May 24, 2006.