Engine Retrofits: Something Old, Something New

Dec 28, 2008
By David Esler

It's an axiom in aviation that like old soldiers, good business aircraft never die - they just get reengined and keep right on flying. It's the not-so-good ones that fade away.

Putting new engines on old but productive (and often, beloved) airframes has been the mainstay of the modifications business ever since the former Garrett Turbine Engine Co. (now Honeywell Engines) removed the Lockheed JetStar's original Pratt & Whitney JT12 turbojets and screwed four of the then-new TFE731-3 turbofans into the airplane's broad tail-mounted nacelles, and gave the airplane a new Stage 3 noise-compliant lease on life and considerably longer legs. (Trivia question: What famous aeronautical engineer designed the nacelle for the 731 JetStar conversion?*) GTEC retrofitted 40 of them, which performed so well that Lockheed decided to adopt the modification, returning the aircraft to production as the JetStar II.

GTEC followed the JetStar mod with a TFE731-3 retrofit for the even more popular Hawker 125-400 and -600 midsize jet, replacing the original-equipment Rolls-Royce Vipers. After turning out about a hundred of the conversions, British Aerospace, which had inherited the Hawker program as part of its U.K. aviation industry consolidation, decided it might be a good idea to upgrade the aging design and launched the TFE731-powered Hawker 700, which was followed by the even more popular Model 800 and 800XP, the latter now produced by Beechcraft in the United States.

In the mid-1980s, Garrett turned its attention to the Dassault Falcon 20, another iconic midsize business jet, and replaced the airplane's factory-installed General Electric CF700 aft-fan engines with its new TFE731-5AR engine. Since the modification literally transformed the Falcon 20, nearly doubling its range and greatly enhancing its altitude performance, GTEC was able to market 125 of the conversions, or about two-thirds of the fleet.

The Tradition Continues . . .

All three of these reengined types continue to fly, some of the airframes more than 40 years old. With new-technology power, it seems you can't keep a good airframe down (another axiom, not to mention a pun), and today a number of enterprising modifiers are making good livings installing new engines on older second-generation business jets like the Cessna Citation 500 series and aging turboprops, including several variants of the venerable Beech King Air. And some OEMs, like Honeywell, are upgrading older jet engines to later dash numbers to enhance the performance of aircraft like another Dassault product, the Falcon 50 trijet.

Uvalde, Texas-based Sierra Industries was modifying Cessna 210 piston singles by removing the gear doors back in the early 1980s when its founder and CEO Mark Huffstutler purchased the former Robinson Aircraft Corp. and that modifier's 120 STCs, two of which involved wing modifications to the Citation I. And that got Huffstutler into the straight-wing Citation enhancement business.

The Citation STCs were the so-called "long-wing" and "Eagle" mods, the latter a cuff to the inboard section of the wing, from root to mid-span, changing the airfoil to reduce drag and creating space for the addition of more fuel. The Eagle mod provided drag reduction and doubled the range of the early Citation 500 from under 1,000 nm to more than 1,800 nm.

Meanwhile, the long-wing mod increased the Citation 500's total wingspan by four feet. "We still install them today and have 30 percent of the fleet modified with those two mods," Huffstutler told Business & Commercial Aviation. Along the way, Sierra acquired four more companies that also possessed STCs, one of which was Century Aircraft, which in 1990 had certified an upgrade to install the Citation II engine, the Pratt & Whitney Canada JT15D-4, on the Citation I airframe, increasing thrust to 2,500 pounds per side. "That was our first exposure to the engine retrofit business," Huffstutler said.

This provided a good business until the late 1990s when P&WC dropped the JT15D from production. "We could only get them off crashed Citation IIs, and we were literally reading NTSB reports looking for crashes," Huffstutler said. "We became the ambulance chasers of the engine retrofit business!" Ultimately the shortage of JT15D-4 engines led Sierra to Williams International, whose engineers were working with Swearingen Aircraft on the SJ30 in nearby San Antonio. "Their business development guy drove out to Uvalde and introduced himself to us, and we developed a good rapport. Out of those conversations we began looking at re-engining the Learjet 20 series with the FJ44-1. For various reasons, we never flew one, but that exposure cemented our relationship with Williams."

Birthing Eagle IIs and Stallions

When Williams announced the FJ44-2 engine for the Cessna CJ2, Huffstutler saw an opportunity. "We immediately said we wanted it for the older Citation series, and the Eagle II was born," he said. "This was the combination of the Eagle wing cuff mod and the new FJ44-2. We got that certificated in 2002, and in 2006, we separated the engine mod and gained approval to do just the engine upgrade on the Citation 500, creating the Stallion."

Both upgrades saw 50- to 55-knot increases in maximum cruise speed on the same fuel burn as the JT15D, or a 400- to 500-mile range increase on the Stallion if throttled back to the unmodified airplane's max cruise speed. For the Eagle II, Huffstutler pointed out, "The flight penalty at top speed is eight knots, but you get another hour of cruise, or a 350-nm range increase, since you're carrying 100 gallons more fuel [in the wing cuff]." Both aircraft are claimed to be able to take off at gross weight and climb straight to the maximum cruise altitude of 43,000 feet in less than 25 minutes and cruise at Mmo. "Thus, we feel we've matched the optimum engine and airframe combination with these mods."

The natural evolution was to the Citation II and S/II. "What made that possible was Williams certifying the FJ44-3 for the CJ3," Huffstutler said. "That engine is larger, with 2,820 pounds of installed thrust [i.e., it's a 3,000-pound thermodynamic thrust rated engine]. This made the engine available for the II and S/II." The resultant performance gain was again a 50- to 55-knot cruise increase on the same fuel flow and the same climb to 43,000 feet in 25 minutes.

"So today we're using two different FJ44s and have created four products around them, the reengined Citation 500, 501, 550 and the S550," Huffstutler continued. "There are about 1,800 aircraft in the fleet that we can modify. You can get these mods done today rather than having to wait several years to deal with the Cessna backlog for new CJs. Furthermore, the Citation service network is geared more toward the legacy airframes than the new ones, so there's lots of support out there for the older ones." Beyond the performance improvement, there are environmental benefits in the retrofits: The engines are quieter and produce dramatically less emissions and, thus, are greener. "Of the 48 we've done, we have a half dozen of them in Europe," Huffstutler said.

The modifier claimed that with the Williams engines, "there's no combination of weight, temperature or field elevation on any of our products where you can't depart and go straight to max cruise altitude. On a summer day in Aspen, we can take off at gross weight and go straight to max cruise altitude. The Lindsey 4 departure requires 400 feet per nautical mile minimum climb gradient, and we can exceed that at max gross at 80 to 85 degrees [F] by a large margin and go straight to max cruise altitude without a step climb. It's all about power."

Operators also benefit from Williams' Total Assurance Program, a power-by-the-hour maintenance service scheme where, for example, at the Elite level of the program, the operator pays $105 per hour per engine for total coverage. This includes loaners during overhauls of the operator's engines. TBO is 3,500 hours for the Dash 2 and 4,000 hours for the Dash 3. "They are FADEC engines, so it's pretty hard to abuse them," Huffstutler said.

The Stallion mod is priced at $1.635 million, which can be discounted by $50/hour credits for time remaining on the JT15Ds that are removed. A $25,000 discount is also accorded if the operator's aircraft was not equipped with thrust reversers. "All aircraft leave us with no thrust reversers, as there is no thrust reverser design for the Williams engine, which really doesn't need it," Huffstutler explained. "Once you touch down, the engines spool down to an idle setting eliminating residual thrust, so reversers or the paddle-type attenuators of the CJ aren't needed. Takeoff distance is reduced by 20 to 40 percent and landing distance remains the same or less." In the modification, different inlet, exhaust nozzle and after body components are substituted, but the remainder of the original nacelle is retained.

The Eagle II conversion goes out the installation center door for $1.785 million, including the wing cuff. The same discount applies for time remaining and thrust reversers. For the renamed Super II and S/II, the price is $1.929 million, with a $60-per-hour engine credit for the JT15Ds and, again, a $25,000 credit for no thrust reversers.

New-Airplane Performance at Half the Price?

The Stallion and Eagle II are claimed to equal the CJ2 in performance; however, considering all-up cost for the conversions and the value of the airframe, they tip the cost scale at half the price of a new CJ2. "So we can also build full aircraft at spec," Huffstutler said, "and have done 12 Stallions and Eagle IIs, as well as two of the Super II and S/II variants." In terms of customer aircraft modifications, Sierra has completed 32 Model 500s and four 501s. "So all together, there are 48 total modified airplanes flying," Huffstutler said. The installations take 14 weeks, including paint on affected areas.

In addition to its Uvalde FBO and repair station, Sierra has licensed Eagle Creek, an independent installation facility at Indianapolis, to do the mods and is negotiating with others in the United States and abroad. "We've developed a kit that can be installed in the field, so our future plan would be to create some alliances," Huffstutler said. "We have two levels of representation outside the company, authorized sales reps who do the sales and installation dealers who can both sell and install. We will leverage our products with other installation facilities so the growth and market penetration is not limited by our facility size."

Sierra is the third largest purchaser of Williams engines after Cessna and Beech and this year acquired its 100th FJ44 for its 50th conversion. "The financial meltdown offers another angle in our marketing, as we can offer an airplane at half the cost of the new ones," Huffstutler said. "All we need to snag is half a percent of the market, and we will be busting at the seams, doing 18 to 20 a year."

At Clifford Development Group in Toledo, Ohio, they hope to snag more than a few, too. In the last two months, Clifford was to have certificated FJ44-3A conversions for the Citation II and S/II after more than a year of ground and flight testing. The company was founded by "aviation vets who grew up in the Duncan and Gulfstream worlds," according to Clifford President Jim Clifford. "We formed in early 2006 to look at available engine technologies and marry them with legacy aircraft to gain a minimum 25-percent increase in performance. The Citation II and S/II represented a large fleet of aircraft, and the Williams FJ44 fits that aircraft well."

"What we've done is try to look at all the airplanes we may be doing and design components and systems in modular fashion that can be allied to a range of aircraft types," Clifford continued. "In addition to the Citation II and S/II, we are looking at additional Citation models, Beechjets, and the Learjet 30 series and up. Among our group, we have collectively earned well over 3,000 STCs applying from light turboprops to GVs, so we have the experience to do this."

Clifford hopes to do this "in a benign fashion" by not making major changes in structure that would compromise the integrity of the airframe and create problems with the OEMs that built and are obligated to support the aircraft. "We put 36 improvements into the airplane [in this case the two Citation models] as we do the engine change. We do not mess with the manufacturer's primary airframe structure, using the existing carry-through beam, while Sierra Industries does a new front one."

The bleed air intercoolers, anti-ice valves and pressurization bleed air flow packs for the retrofit are all off-the-shelf CJ3 and Citation V Cessna parts. "We are doing that because the C550 components are not rated for the temps and pressures associated with the Williams engine," Clifford said. "We incorporate heavy duty brakes, as we're removing the thrust reversers for 'operator comfort' even though the FADEC engine can idle lower than the hydromechanically controlled JT15D or FJ44-2 and -2A, which had idle speeds set for go-arounds." (The FADEC-equipped engines can spool up to full power in three seconds, while the hydromechanical variants require eight seconds, and the FAA requires less than eight seconds.)
Marrying the Engine to the Systems and Entering the Digital Age

A digital engine instrument package by Ametek, originally built for the later Citation 560 types and the Excel and Bravo, will replace the original tape-style gauges. "We install the electrical and control systems as modules, so all the harnesses are pre-built with relays in panels, prefabricated and tested, so it takes only 1,000 [man]hours to install one of our kits, or eight to 10 weeks," Clifford said.

The center console is rebuilt so the RVDT, a proximity device that telegraphs thrust lever position to the FADEC, can be mounted with a short linkage to the levers, replacing the original cables that extended from the levers to the hell hole. Clifford claimed the original arrangement required considerable maintenance, since over time the cables become stretched. The pedestal is also extended to accommodate avionics relocated from the instrument panel - the autopilot controller, FMSes - freeing up space there for new avionics; there is an option for two extension lengths. "Eliminating the throttle cables creates more depth for avionics installations," Clifford explained. Mechanical Mach and gear warnings are also replaced by picking off the digital signals from the engine FADEC. "In this business, you can hang the engine to the side of the airframe or you can marry it to the rest of the aircraft systems, which we prefer."

Starter generators have been known to have a short brush life in the stock aircraft, so Clifford redirects bypass air to the generators for cooling; same for the intercoolers. The old Peri bleed air seals in the engine cowl are replaced with new bellows-type seals that are claimed not to leak. The fuel flow system is brought up to the digital age with a digital fuel flow transmitter so both fuel flow and quantity can be displayed on the Ametek instruments array. Quick-donning O2 masks by Eros are added, as Clifford plans to increase the Model 550/S550 service ceiling down the road by perhaps 2,000 feet to 41,000 feet for better fuel flow (the original aircraft were certified for 39,000 feet).

"We have also looked at adding more thrust from the engine," Clifford said, "so we have increased the thickness of the pylon skins from 0.025 inches to 0.032 inches for more structural integrity [as Cessna did on the Citation V]." Starter cables and fuel lines have been upgraded, with the ground wire moved from engine pylon to battery to reduce the possibility of corrosion in the original grounding location that caused split amperage between the two engine-driven generators. Finally, a new Hawker 48-amp-hour battery backed by a five-year warranty is added.

"Due to the dimensions of the Williams engine, we cause a forward shift in the c.g. by 2.5 inches," Clifford said, "eliminating the aft bias in the balance envelope of the JT15D installation. We also eliminate 90 pounds of weight per side since the Williams engine is lighter and because we remove the thrust reversers. We also save about 70 additional pounds through the installation, mostly the cables and wire bundles that are eliminated because of the digital engines."

Clifford has also developed a winglet for the Citation that will be installed on the S/II; it is described in the winglet report elsewhere in this issue. On the S/II, the engine mod was certified first without the winglets, approval for which will follow in second quarter 2009. "We have three service centers appointed around the country and will pick up two more before the end of the year," Clifford said. "They will do installations for us, as we do not own an installation center ourselves." Meanwhile, Clifford will manufacture the conversion kits under contract with Great Lakes Aviation in Kalamazoo, Mich.

The first customer aircraft was scheduled to be dispatched to South Africa this month from Great Lakes Aviation. "We will deliver aircraft with approved performance enhancement data in the flight manual," Clifford said, "so the operator does not have to interpolate from the original manual. We have 24 engines ordered for 2009 and will deliver five aircraft before the end of 2008. And we have orders booked for next year. [He refused to state how many.] Not only that, but we are working with a select group of brokers who will buy aircraft and modify them on spec."

Clifford's price for the Citation II conversion is $2.185 million in 2008 dollars; the S/II is $2.275 million, also in 2008 dollars. Pricing in 2009 will increase to $2.295 million for the Citation II and to $2.395 million for the S/II. All of Clifford's 36 improvement mods are included in the prices, including the S/II's winglets. The engine retrofits are also certified to meet Stage 4 noise limits.

Going High: An Upgraded Raptor

Moving to the high end of the business jet spectrum, the Falcon 50Dash4 program is an example of an engine upgrade, where instead of installing a new and often different engine on the airframe, the aircraft's existing powerplants are upgraded to a later variant of the engine type, in this case from the Honeywell TFE731-3 to Dash 4 configuration. Developed by Ken Goldsmith of Yankee Pacific Aviation, the 50Dash4 was described in some detail in a flight report by Fred George that appeared in the December 2006 issue of Business & Commercial Aviation (page 52). In this article, we will bring the program up to date.

Goldsmith's partner in the 50Dash4 program is East Alton, Ill.-based Premier Aircraft, LLC. As described by engineer Ken Shimabukuro, who serves as program manager, the Dash 3 engine conversion involves a new fan, gearbox and complete hot section adapted from the later variant of the engine, the TFE731-4. The work is accomplished by Honeywell at its Phoenix factory.

On the Falcon 50 airframe, the nozzles are exchanged from the stock long to a new short configuration to accommodate the Dash 4 engine's different turbine flanges and to promote enhanced performance. "We also get lower noise emissions from the new nozzle due to better mixing, which is accomplished inside the nacelle as opposed to the Dash 3 doing it externally," Shimabukuro said. "We are Stage 4-certified, thanks to the nozzle and based on our flight trials over the microphone array at Bakersfield [Calif.]."

In the number one and three engines, the high-pressure bleed ducts are replaced for better clearance, as the Dash 4 engine diameter is larger. The center engine does not require the modification. The ITT gauges on the panel are remarked to accommodate new temp limits, and Honeywell reprograms the N1 digital engine electronic control.

The Dash 4 develops more thrust during climb and cruise and is flat-rated to a higher temperature, or 92°F, while the Dash 3 is rated at 76°F. "We get a 20-percent reduction in time to climb," Shimabukuro claimed. "To get to 37,000 feet in the unmodified Falcon 50 would require 28 minutes, and in reality at MTOW, it probably won't make it to that altitude at all. The modified airplane takes 22 minutes to do it." Premier says the 50Dash4 can climb directly to 39,000 feet at max takeoff weight and that customers who've purchased the upgrade are claiming it actually exceeds performance manual figures.

Max cruise speeds are up 20-plus knots. Range at 0.75 Mach and four passengers aboard has been increased to 3,250 nm from the unmodified airplane's 3,000 nm. At the 0.80 Mach high-speed cruise, the Dash 4 will go 3,000 nm vs. 2,700 nm for the Dash 3. Shimabukuro credited the improved fuel burn to the updated technology added to the engine and the nozzle changes. "Altogether, it does about 80 percent of what the new Falcon 50EX Dash 40 airplane does," he said. (Honeywell itself sold a Falcon 50 engine retrofit early in the decade in which it installed the second generation TFE731-40 in place of the old Dash 3s. Only a handful of the retrofits were completed before the company shut the program down due primarily to the more than $6 million cost of the mod.)

The 50Dash4 upgrade was certificated in 2007, and initial installations were conducted at West Star Aviation in East Alton. Recently, however, Premier announced Jet Aviation/Midcoast as a second installation center, providing the modifier with an entre into the European market. Accordingly, the company has filed for an EASA approval so that the work can be performed at Jet Aviation's European facilities.

Pricing is variable. For an operator whose engines are not covered by Honeywell's Maintenance Service Plan (MSP, or in the vernacular, "money sent to Phoenix"), the straight-up price is $2.305 million. "Because we are supported by Honeywell, they are making credits available to customers through their MSP accounts," Premier President Jim Swehla said. "So each airplane is different depending on where it is in the maintenance cycle. If they are coming up on MPI or CZI, they would have more money in the account, and those credits could be applied to the $2.305 million figure. For example, if an operator is coming up on three core inspections, his credit could bring it down to as low as $1.7 million."

Since certification, Premier has completed six conversions and Swehla thought the company could turn out at least one and perhaps two more by year-end. "Europe looks good as a market, too," he said. "There were 251 Falcon 50s built, and seven were converted to the Honeywell Dash 40 engine and a few were damaged in accidents and taken out of service. Our business case is 25 percent of the 240 or so remaining." Premier also offers an avionics upgrade to complement the engine upgrade; either Rockwell Collins Pro Line 21 or Universal EFI-890 avionics suites can be retrofitted by West Star. "Of the six we have done so far," Swehla said, "five either have or will get the Pro Line panel."

Growing Your Engine:Honeywell Upgrades and Conversions

Honeywell breaks its engine support and growth program down into three distinct areas: retrofits, mods (or conversions, a la the Falcon 50Dash40 program) and upgrades, or RMU for short.

In ascending complexity and cost, it starts with upgrades. According to Steve Gomez, Honeywell Engines' manager, technical sales, propulsion and safety products, this is "where we are doing something to the engine and changing its designation for the purpose of improving reliability, durability, operability [like ITT margin increases] and cost of ownership." An example would be an improvement to an engine's turbine section.

Upgrade programs currently offered by Honeywell include TFE731-2 to -2C for the Learjet 31 and 35/36 and Falcon 10 or 100; -3A to -3C for the Learjet 55 and Westwind Astra; and -3 to -3D for the Falcon 50, Hawker 700 (and 400 and 600 retrofitted airplanes), Sabreliner 65, Westwind and JetStar II. For all three of these upgrades, MPI inspection intervals are boosted from 1,400 to 2,100 hours with no change for CZI. A fourth program involves the second-generation TFE731-20R to -20AR for the Learjet 40/45.

"So we look at where newer technology in terms of engineering or materials could be incorporated into an earlier version," Gomez said. "On the Dash 2 to 2C, the original solid HP turbine blades were exchanged for the later variant's cooled-blade technology, which was developed as the engine matured."

For upgrade pricing, kits range from an average of approximately $100,000 to $126,000 per engine, if purchased by operators enlisted in MSP (i.e., MSP holders get a discount on the kits). For operators without MSP, prices would rise as high as $183,000 to $225,000, since Honeywell would not know the condition of the non-MSP engine. Non-MSP operators who buy the kits are offered no-charge enrollment into MSP. For the -20R to -20AR on the Lear 40/45, the non-MSP operator will pay $62,000; however, MSP operators receive it free at MPI.

The next level of program is modifications, or conversions. "The TFE731-3 to -4 is a conversion program," Gomez said. "As an example, we look at the previous benefits provided under upgrades, and in place of them we add performance improvements, either thrust or TSFC [in the case of the -3 to -4, it is a thrust improvement]. For cost of ownership programs, the things we affect are reduced MSP rates, potentially reduced MSP enrollment rates, and extended maintenance intervals. Another example of a conversion program is Dash 5AR to 5BR. The first 100 Falcon 900A airplanes were Dash 5AR-powered, and since 1991, we have converted approximately 90 of them to the Dash 5BR configuration, thereby creating the Falcon 900B variant."

Current conversion programs include -20AR to -20BR for later Learjet 40/45s sold through Bombardier, providing improved hot and high performance; -3 to -4 for the Falcon 50Dash4 program; and -5A to -5B for the Falcon 900A to B, improving BFL, time to climb and range, as well as extending hot section and overhaul intervals to 2,500 hours MPI and 5,000 hours CZI from, respectively, 2,100 and 4,200 hours. Pricing for the -5A to -5B runs between $400,000 and $485,000 per engine for non-MSP, depending on number of hours on the engines. MSP operators get reduced pricing based on hours they've flown since the last maintenance event, dropping it as low as $200,000 to $240,000.

The OEM also offers modifications for its TPE331 turboprop engine, converting the -3, -5, -6 and -8 to the -10 configuration that produces more power. The -5 and -6s are used in Twin Commanders and Mitsubishi MU-2s; the -5 is on the Dornier 228, the -8 powers the Conquest; the -3 motivates the Fairchild Merlin and Metro; and the B100 King Air uses the -6. The TPE331 conversions are all performed by StandardAero.

Honeywell is currently not offering any engine retrofit programs, as described at the beginning of this report, where entire engines are swapped for newer variants. The most recent was the now-defunct Dash 40 exchange for the Falcon 50. "But we are constantly evaluating the fleet on a regular basis to look for [retrofit] candidates to pass value to the customer," Gomez said.

Some of the upgrades are installed by authorized facilities; however, because conversions result in thrust and TSFC improvements and subject engines are being changed to different configurations, conversions are done only by Honeywell.

"We want to stand by the product in the field, but over and above that, if there is an opportunity to inject new technology for the operator, we want to do that," Gomez said. "We want to keep the product technically and financially competitive."

New Power for the King

One of the most popular airframes for engine retrofits is the Beech King Air, not just because of its numbers - the airplane has been in continuous production since the early 1960s - but its utility. In all its variants, the King Air has amassed a committed following of users, ranging from business aviation and commercial operators to military services. Thus, it shouldn't be surprising that this popular and long-lived type would capture the attention of modifiers.

One of the largest turboprop reengining programs in the conversions business is operated by Blackhawk Modifications, Inc., of Waco, Texas, which addresses four variants of the King Air - the C90, E90, 200 and B200 - as well as the Cessna Conquest I and Piper Cheyenne I, II and IXL. The King Air line, however, is Blackhawk's bread-and-butter business.

"We started in 1999 with three partners and the STC for the PT6A-135A retrofit for the Conquest I," Blackhawk's Jim Allmon, president and CEO, told Business & Commercial Aviation. The King Air work began in 2002, when Blackhawk purchased an STC from Swearingen to install PT6A-135As in C90 and E90 airframes. "We spent a lot of money cleaning that one up," Allmon said, "as it dated from the 1970s and there have been some regulatory changes since then. Then we bought the STC from Stevens Aviation to replace the PT6A-41 on the King Air 200 with the Dash 42." This was followed by development of an in-house STC to install the PT6A-61 and -52 on the King Air 200 and B200. In 2006, Blackhawk rounded out its portfolio by acquiring an STC for the Cheyenne I, II and IIXL governing the replacement of original PT6A-11, -28 or -135 engines with the -135A rated, respectively, in the three Cheyenne variants, at 500, 640 or 680 shp.

"We've done about 204 total conversions of all types, distributed among several installation shops," Allmon said. "We are the only engine retrofit company exclusively endorsed by Beech and supported by Hawker Beech services worldwide for installations."

Blackhawk touts "big performance increases" from its retrofits plus new warranty benefits (see the firm's Web site at www.blackhawkmodifications.com for comparison charts). "The biggest increases are 40 knots on the older C90s and 50 knots on the Cheyenne I's," Allmon said. "For the King Air 200, you will go from 265 knots to 310 knots, a 45-knot increase. On the B200, which can do about 280 to 285 knots, you will still get the 310-knot increase." Range stays relatively the same and any additional fuel burned is claimed to be made up for through the speed increases (i.e., you get there faster). "The big advantage is altitude," Allmon claimed, as "you can go up to 28,000 feet in the C90 as opposed to the usual 18,000 feet."

Painting the C90 Dollar-Green

Blackhawk has reengined most of the C90 series - by Allmon's count, more than 110 airframes. "The 200s are rapidly catching up," he said, "roughly 55 in just two years." While all the conversions are similar, the -61 and -52 require some mods to the airframe. Because the PT6A variants have one less bleed valve, Blackhawk has installers patch the extra vent on the airframe and re-mark the engine gauges. Additionally, Allmon said, "We require the lightweight exhaust stack because the old stovepipe stacks are heavy, and the engines are heavier by 42 pounds than the Dash 41/42s, and so to cut down on that weight we went to a lightweight exhaust stack produced by Frakes or Beech, the D4 stack, which is eight pounds lighter per stack." Most later B200s are already equipped with the D4 stack. The conversion also requires four-blade props that, again, most B200s already have.

"We flat-rate to 850 shp from 1,218 shp - the Dash 42 is 1,042 shp - so we have more residual horsepower at higher altitude," Allmon said. "This gives us the 310-knot cruise speed, and the really nice thing is that you can fly into the flight levels much easier if you're RVSM-approved, all the way up to FL 350. We have flown it at FL 350 and gotten 290 knots, as opposed to 230, if you could get up there with the Dash 42, which you can't very easily.

"It'll burn around 10 gph to 12 gph more fuel than the Dash 42," Allmon continued, "but you're getting more speed and climb to offset that. So on a typical trip, you'd probably burn 10 gallons to 15 gallons more fuel for a four-hour duration. You're putting fewer cycles on the airplane, too. If you're flying 100,000 miles per year, you can do that in fewer cycles because you don't have to land as often to refuel. With the old engines, that will take you 350 hours; with the new engines, it will take you 300 hours, so there will be fewer maintenance events per year."

For all the -135A conversions irrespective of the airframe type, the price is the same: $629,000, exchange (i.e., for the old engines), plus $25,000 to $30,000 for the installation. The -42 retrofit for the King Air 200 is priced at $815,000, exchange, plus around $20,000 for the installation. For the -61 King Air 200 or B200 job, the price is $870,000, exchange. This program also requires that the full Raisbeck Epic kit that includes new props, strakes, a ram air recovery system and wing leading edges be installed. Epic runs about $110,000 plus installation of 200 hours of labor; the engine installation is another $20,000, or about $40,000 total for Epic and engine installation labor. The -52 is $915,000 and does not require the Raisbeck kit; installation is $25,000.

Allmon provided an interesting price comparison between overhauling run-out PT6As and installing new ones with increased performance. "You have three King Airs, all equally equipped. Airplane A has a $1 million base value, and its Dash 41 engines are run out. So the owner decides to overhaul, and because his engines are clean, he pays $700,000 for the overhaul. He has invested $1.7 million in his airplane and four weeks downtime. If the owner sells the airplane, he can get $1.8 million for it, and so he's made $100,000.

"Airplane B is also worth $1 million but has run-out engines in really bad shape," Allmon continued, "and the owner gets the bad news at overhaul time that his work is going to run $900,000, not an unusual price for a set of abused engines. So now he has $1.9 million invested. If he sells, he probably can't expect to get the same price that the owner of Airplane A got, so he sells for $1.8 million and loses $100,000.

"Now," he concluded, "Airplane C owner decides to go with our Dash 61 mod for $870,000 and has $1.870 million invested. Knowing that new engines with more power and performance historically increase the value of an airplane, if he sells, he can probably get, conservatively, $1.950 million, so he's made $80,000 with no gambling on overhauls. Airplane A has to roll the dice on the overhaul because he doesn't know how much his overhaul is going to cost until the shop opens up the engines. And at the end of the day, with the retrofit, you also get a better performing airplane."

At the NBAA Convention in October at Orlando, StandardAero announced a competing King Air 200 retrofit, exchanging the type's PT6A-41 turboprops for new -42s. "What you get is new engines with improved performance in the aircraft of 10 to 15 knots cruise speed," Manny Atwal, general manager of StandardAero's PT6 division at Winnipeg, told Business & Commercial Aviation. The impetus compelling the King Air 200 operator to consider doing the retrofit is the claim that after a second or third -41 overhaul, the cost differential between a rebuild and new engines is biased in favor of the latter. The program was certified in August 2008, and priced at $815,000 per airframe, all-in.

"There are no significant airframe mods beyond some brackets in the nacelles, so it's pretty much a direct swap," Atwal said. "The exchange takes five days or less, and we can do it anywhere in North America, either at our facilities or yours, as the installation is not complicated. We can even do it on-site at your location with one of our field-service teams." Four StandardAero -42 retrofits are flying now and the modifier claims to have orders booked through the end of this year.

Enter the Walter

The big news in King Air retrofits, though, is the Walter turboprop now being imported from the Czech Republic and celebrated as a rugged and vastly less expensive alternative to P&WC's PT6A. And the entity making those claims is none other than General Electric Aviation, which bought the entire Walter Aircraft Engines operation in Prague last July as part of an extensive expansion of its business aviation product line. (The means by which "Generous Electric" is apparently going about this is through acquisitions and partnerships, e.g., its joint venture with Honda to develop the HF120 entry-level turbofan.)

Founded in 1913 as a bicycle manufacturer, Walter eventually transitioned into internal combustion engines and later in the 20th century built powerplants under license for the German Luftwaffe in World War II and, afterward, the Soviet Union. The firm conceived its M601 turboprop, a 700-shp-class engine, in the early 1970s as its first fully in-house project, obtaining certification in 1975.

According to GE Aviation chief marketing officer Chet Fuller, the M601 was designed for simplicity, robustness, and easy installation and removal. "All of the LRUs are attached to it when it ships, and all the operator does is connect it to the airframe," he said. The engine features an automated starting sequence and can be fired up safely - that is, without worries of hot starts - by pushing a single button. Furthermore, it requires no hot section inspection and is designed for rugged conditions.

"Our goal was to take that simple design and add GE materials and aerodynamics while retaining the simplicity of the design," Fuller said. "The beautiful thing about it is that it uses a sling-ring fuel injector in the combustor with eight holes in it and no nozzles. There is only one moveable part and that's the ring, and it's a low-pressure fuel system, so it simplifies the fuel control and the metering. There's much lower risk for fuel leaks, and it ends up creating a system with excellent relight characteristics and burn efficiency. Nozzles are a huge cost-of-inspection item. It uses a torch igniter, which is very reliable." Another cost-saving feature is the M601's sheet metal cases.

GE's first move, once it had acquired Walter, was to go through the engine and update it. "We are replacing the current alloys, which are Russian-spec, with those of Western standard, such as Inconel, nothing exotic, very standard, and it allows us to reduce the material costs," Fuller elaborated. "We also applied second-generation 3-D aero design, which is the same technology level as was used to design the airfoils for the GEnx engine for the 747-8. Those latest-generation CFD tools allow us to improve the aerodynamics of the compressor and the turbine, and so when we put in Western standards, we not only reduce the cost but also reduce the variations of the materials, and that allows us to increase both the temperature and pressure of the engine and increase the margins to new levels."

From the current variant of the engine, the M601F, GE has spawned the M601H-80. The former was flat rated at 777 shp at 24°C ambient, while the H-80 will be capable of 800 shp at 36°C. "Not only will this give you great hot-and-high performance, but the altitude performance will be enhanced," Fuller said. Thinking of applications, he speculated, "We think the right STC for the King Air C90 with new props matched to the engine will exceed the performance of the PT6A-42 and get 30 knots better in the low '20s [i.e., 23,000 feet to 25,000 feet]."

Before GE showed an interest in Walter, the M601 had made somewhat of a splash among modifiers in the United States, and at least four STCs have been developed to install the engine in the King Air. Two conversion scenarios make sense to Fuller. "One uses the M601E-11, which is a remanufactured engine with a 2,000-hour TBO and no interim inspection and which will get you comparable performance to today's PT6s but for significantly lower cost. The other conversion that makes a lot of sense to us from a value standpoint and which would be a performance-enhancing conversion uses the H-80 new engine with a 3,000-hour TBO, no HSI or nozzles, much lower maintenance costs, equivalent fuel burn and enhanced performance. So we think there are two distinct markets there."

(It should be noted that while Walter M601F and M601E engines produced before GE's purchase of the company are placarded with either 2,000- or 3,000-hour TBOs, they also carry a "calendar-specified" TBO of five years, meaning that an operator with, say 3,000-hour engines who flies only 250 or 300 hours a year will reach TBO before running out the powerplants in terms of hours. Reportedly, Walter, under some circumstances and upon request, can extend the calendar TBO two more years and, in some cases, three years. According to GE, under its auspices since taking over the program, the M601-H80 engine will have the calendar limit removed entirely and TBO will reflect the specified hourly limits.)

The first market would be for the value-conscious customer - what Fuller called "a slam-dunk" - and the second would be for the performance-oriented operator. "Our plan is to have both conversions available by the end of next year. We are evaluating the current STCs out there today. We plan on developing a turnkey solution for customers with [modification] partners for E-11 and H-80 conversions, and we're canvassing the marketplace now and sending our engineers to each of the groups owning the STCs, weighing the pluses and minuses of each."

GE believes its product support must be "preeminent" to the customer in this business case. "So our associating ourselves with an STC will require that the people who do and support them and their engineering is consistent with the brand, quality and product delivery that is the expectation of people who buy GE products," Fuller promised. "So what that means is that when you get your King Air conversion, you will know what your warranties and limitations are, you'll have flight test-verified book performance data, who to go to for product support, and who to call if there's ever a problem, because that's the brand promise of GE. . . . In this segment of the market there are a lot of owner/operators, and we have to create a system that supports them."

With its purchase of Walter and shepherding the M601 engine, is GE going head to head with P&WC in the turboprop marketplace? "The world deserves a choice," Fuller answered. "Our plan is to provide a better engine at a lower cost and provide an alternative to what has been virtually a monopoly. There are 1,500 Walter engines out there, but the company has been resource-constrained, and we will spend $1.5 billon on company-funded research this year. Much of that money is [supporting] basic research - aerodynamics, tools, materials."

So moving into a new market segment with the Walter is just a natural leveraging of GE's resources, Fuller insisted. "This engine is very manufacturable and is in a low-cost infrastructure. It works very well and we know there is a market starving for an alternative. We're gonna' take this simple, durable, rugged engine, give it better reliability, equal fuel burn [to the PT6A], lower cost and wrap it in a product support environment that the customer never has to worry about. That's the goal."

And One of Those Walter STCs

At least nine King Airs were converted to Walter M601 power before GE purchased the Czech manufacturer last summer. Seven of them were done by Scottsdale, Ariz.-based Performance Conversions, Inc. The company is owned by Robert Turnage, who made his money in the semiconductor and real estate business before being drawn into aviation modifications as a "silent investor" with two partners who were running the operation out of a mod center in Wisconsin and had earned an STC in 1999 to replace the PT6A-20 and -21s in the King Air C90 and E90 with the Walter M601-11A engine.

Eventually, Turnage bought out his partners and took possession of the STC, and when Business & Commercial Aviation had caught up with him he was reorganizing the company and had cut a contract with XN Air, a Washington-based mod center, to do future conversions. "We convert from the firewall forward," he said, "using the same mounts modified only slightly. The only major change results from the fact that the engine is four inches longer, requiring some sheet-metal work on the nacelle." The cowlings are retained and extended to accommodate the additional length of the engine.

New Avia five-blade V510 props, also built in the Czech Republic, are installed as part of the conversion. The prop is turned slower by the M601 and, due to its smaller diameter, the tips are further away from the fuselage, reducing noise in the cabin. Additionally, Raisbeck strakes are mounted on the aft fuselage to allow a useful load increase to 10,100 pounds. The conversion takes about 45 days, including the strakes.

"The Pratts develop 450 shp, and the Walter develops 750 shp," Turnage said. "The A in the [-11A] designation is for 'altitude,' allowing this conversion to fly as high as 30,000 feet. The engines are flat rated to 550 shp. The ceiling, of course, is increased from about 25,000 feet to 30,000 feet. It has so much power at altitude you can reduce the power to about 73 percent and get 73 gallons per hour, about the same as the original PT6As."

Turnage also stressed the maintenance advantages of the Walter engine, claiming it "needs only an oil change and new filter every 300 hours. The Pratts have to go through a fuel nozzle inspection and the hot section at midlife for $60,000 to $80,000, and the TBO is 3,500 hours. The Walter does not require a hot section and the TBO is 3,000 hours. The reserve is $45 an hour and includes the overhaul."

The modifier sells two versions for the conversion. In addition to the 3,000-hour TBO -11A, Performance Conversions can also provide a remanufactured engine rated at 2,000 hours, the latter for operators who would be using the aircraft less. "Additionally, we offer remanufactured engines with both short and long TBOs for less money," Turnage said. "We put together the kits and have authorized XN Air to do the installations. Other conversion centers can do the work with agreement from us."

The conversion cost is approximately $280,000. The engines range in price from $154,000 for a 2,000-hour remanned M601-11A to $300,200 for a 3,000-hour new engine. Props are included in the conversion cost. (The kit also includes installation manuals and documents and PMA airframe and engine parts.)

"We do not accept trade-ins for the original PT6A engines, and the customer can sell them," Turnage said. "Engine rebuilders claim that the Dash 20, which P&WC doesn't support any longer, is worth only $15,000 and the prop between $8,000 and $10,000. For the Dash 21, the range is $50,000 to $80,000. In both cases, they give the owner of the engines money for the hours remaining, or $500 per hour." This can work out to as much as $90,000 or more per engine if 500 hours or more are left on the engine, Turnage claimed. "The money would then defray a large part of the cost of the Walter engine. For example, assume a Dash 21 with 500 hours left. The average price for the core is $65,000, and for $50/hour of unused time, that would bring in $25,000 more. Altogether, a pair would be worth $180,000. To rebuild PT6As today, the price is between $175,000 and $250,000 each, depending on condition."

An undetermined number of the seven Walter engine-converted airplanes are in FAR Part 135 charter service with operators in the United States, while another labors in Sýýo Paulo, Brazil, with a charter operator named, appropriately, Aero Taxi. "Charter operators love the more than 60-percent lower maintenance costs and lowered downtime," Turnage claimed. "Typically, for 300 hours of operation, downtime is four hours for oil and filter changes. No other service on the engine is required to TBO."