Something Old, Something New

The scoop on engine conversions.

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B200 King AirScott Slocum

In 1991, Bobby Bishop and his father were operating a skydiving operation out of Celina, Texas. They had a Cessna 182, a Pilatus PC-6 Porter, a DC-3 and a de Havilland Caribou. But they wanted something in between the Porter and the DC-3/Caribou size aircraft. A de Havilland Twin Otter didn't seem cost-effective, and the single-engine Otter — even one with a 750 shaft-horsepower (shp) conversion — didn't have quite the power they wanted.

"We said, 'What we really need is an Otter with a 1,000 hp engine,'" Bishop remembers.

So Bishop and his dad did the work to get a Supplemental Type Certificate (STC) for replacing the Otter's stock 600 hp Pratt & Whitney 1340 radial engine with a flat-rated, 900 shp Honeywell TPE331-10 turbine engine.

"We figured that even if we never did it again, we could use it in our skydiving operation," Bishop says. But very soon "the Alaska guys heard about this Otter with this huge engine down in Texas," and the phone started to ring.

At the time, the Bishops had gotten only a single-use STC, but an Alaskan bush pilot named Paul Claus sent Bishop, sight unseen, a half-million dollars to do a similar conversion for him. So the Bishops got a multiple-use STC … and found themselves in a new line of work.

Eighteen years later, Texas Turbine Conversions, the company the Bishops founded to do their conversion work, is a thriving business that performs turbine upgrades for both Otters and Cessna Caravans. (The Caravan conversion replaces the stock Pratt & Whitney PT6A-114 600 shp or PT6A-114A 675 shp engine with a flat-rated 900 shp Honeywell TPE331-12JR turboprop engine.)

Of course, Texas Turbines is far from the only engine conversion operation out there. Ever since the Wright brothers figured they could build a better engine if they built one themselves, aviation manufacturers and after-market shops have been hard at work figuring out how to make a better mousetrap. Sometimes, a new engine is simply matched with a new airframe on the production line. But often, even if that happens, inquiring minds soon start thinking about how much better an older model of that airplane would perform if it just had that upgraded engine in it.

In the piston market, any number of individuals modify existing engines into experimental models with different carburetors, bigger pistons or other power-producing modifications. But fewer turbine owners are open to the idea of an experimental engine or airplane. So most turbine "modifications" consist of either an engine manufacturer making certified upgrades to an existing engine, or a shop replacing an older engine with a more capable, newer model — but with an FAA-approved STC, so the aircraft is still a fully certified, insurable product.

Turbine conversions and upgrades are done by both original engine manufacturers, such as Pratt & Whitney and Honeywell, and individual, after-market shops such as Texas Turbines. The individual after-market shops tend to specialize in a few specific modifications for which they own the STC. They also tend to specialize in smaller engines and aircraft, from turboprops to smaller business jets — in part because the cost of obtaining an STC on a Gulfstream V engine would be prohibitively expensive for a small, privately owned company.

At the bottom of the market are shops that convert pistons to turbines. The Otter conversions are now a minor point for Texas Turbines, but there are other shops that offer piston-to-turbine conversions. Soloy, for example, offers certified turbine conversions for 206/207 aircraft, and O&N offers the "Silver Eagle" turbine conversion for the Cessna 210.

A Soloy "Mark II" conversion, which puts a 450 shp Rolls Royce 250 series engine on a Cessna 206, costs about $650,000, but Soloy CEO Dave Stauffer points out that it still offers owners "the lowest-cost single turboprop you can buy." Soloy also offers a number of turbine helicopter conversions, including one that replaces the stock Turbomeca engine on an Aerospatiale AS350 with a Lycoming LTS101 powerplant.

Next up the ladder are the mostly independent shops that offer retrofits for existing turboprop aircraft. One of the most popular, in terms of sheer numbers, is the Blackhawk Modifications Inc. conversion program for older Beechcraft C90 and B200 King Air turboprops. Blackhawk replaces the original Pratt & Whitney engines with newer-model Pratt & Whitney engines. While the new engines are flat-rated to the same horsepower as the old ones, they're capable of holding that rated horsepower to a higher altitude.

"If you increase the amount of horsepower you put on an airframe," explains Edwin Black, director of marketing and sales for Blackhawk, "you have to recertify the airframe as well. So we keep the horsepower the same but flat-rate the engines so the climb and cruise performance are better."

On the other hand, Blackhawk is now in the process of certifying a conversion for the Cessna Caravan that would increase its horsepower by replacing the stock Pratt & Whitney PT6A-114A 675 shp engine with a Pratt & Whitney PT6A-42A engine capable of 850 horsepower.

Conversions for jet aircraft are becoming more popular as well. Engine upgrades for bigger jet aircraft are nothing new — Honeywell has been offering upgrades for its Garrett/Signal/Allied Signal/Honeywell engines since 1977. The first mods consisted of converting turbojet engines to the significantly more efficient turbofan engines, which in some cases, says Steve Lopez, a manager in technical sales for Honeywell, "doubled the range" of aircraft such as the Lockheed Jetstar and early Hawker and Falcon jets.

Subsequent upgrades and retrofits have offered any number of benefits, from longer maintenance intervals and more robust hardware to increased thrust and fuel efficiency. In the case of the Citation III, for example, Honeywell says it has now re-engined the entire fleet from the original TFE731-3B engines to TFE731-3C engines. The upgrade didn't affect aircraft performance any, but Honeywell reports that it significantly increased owners' maintenance intervals.

Independent conversion shops are rarer in the jet market, but there are a few, especially for smaller aircraft. One of the better known is Sierra Industries in Uvalde, Texas, which replaces the stock engines on "legacy" Citation Is and IIs with Williams RJ44-series engines.

"We started off with an STC to put the Pratt & Whitney JT15D-4 engines from the Citation II onto older Citation Is," explains Sierra President Mark Huffstutler. But because those engines were no longer available from Pratt & Whitney by the time Sierra started the conversions, "that depended on us coming up with intact engines out of damaged aircraft," Huffstutler says wryly. "We were like the ambulance chasers of aircraft engines, and it was hard to plan a business that way."

So when Williams approached Sierra with the idea of putting Williams engines in the early Citations instead, the company decided to pursue the STC for that conversion as well. The Williams engines offer a 10 percent to 12 percent thrust increase, Huffstutler says, and as much as a 25 percent reduction in fuel flow. In addition, Williams offers a "power by the hour" plan that Pratt & Whitney doesn't offer for its out-of-production "legacy" engines.

Sierra now offers certified Williams conversions for the Citation I, Citation II and Citation SII. And while customers might initially come in for an engine upgrade, Huffstutler says they usually leave with many other changes as well, including upgraded avionics, new interior, new paint and, in some cases, a longer wing or modified airfoil. The result, he says, is that customers end up "with completely refurbished aircraft with almost the same performance as a new aircraft, but for half the price."

Of course, that begs the question of what the original aircraft manufacturers think of all these after-market upgrades that allow customers better performance without having to buy a new aircraft. And the answer varies.

"Certainly, we would prefer they buy a new airplane," acknowledges Doug Oliver of Cessna.

But several of the after-market shops contend that their customers are not the same as new aircraft buyers.

"The guy who's going to refurbish a [Citation] 501 or a Citation II is not the same guy who's going to buy a CJ2 or a CJ3," Huffstutler says.

Black agrees.

"The general mentality has been that if people upgrade their old airplanes, they won't buy new ones," Black says. "But when Beech came out with the C90GT model in 2006 (which paired a new C90 King Air with the same PT6A-135A engines Blackhawk was putting in older C90 models), they went from selling 20 a year to 60 a year." That's when Beechcraft signed up all the Hawker Beech service centers to distribute Blackhawk products as well.

"They realized that people who want new are going to go buy new, and people who are more frugal will tend to fix up their old plane or make do with what they have," Black concludes.

Of course, even an engine conversion is not cheap when it comes to turbine equipment. A Sierra engine mod typically runs around $1.3 million to $1.4 million for two engines, although Huffstutler points out that overhauling two run-out Pratt & Whitney PT-15D engines can run from $300,000 to $600,000 apiece, so the price isn't necessarily that much higher if the engines are run out anyway.

That point might also account for the fact that the majority of customers who undertake significant engine upgrades or conversions do, indeed, have problematic or run-out engines. If they're going to have to put out a lot of money anyway, paying a little more for a lot more performance and efficiency becomes a more appealing option.

On the other hand, Black says there's also a segment of Blackhawk customers he calls the "performance buyers," who have enough money to do what they want and just want to go faster, no matter what kind of time is left on their engines.

Why don't those performance buyers buy new aircraft? Any number of reasons, including the fact that some are really comfortable with flying their existing aircraft and don't want to have to transition themselves or their crew to a new airplane.

In some cases, a conversion makes sense because, as in the case of the Otters and Caravans that Texas Turbines does, it allows an aircraft to perform in a niche where there is no other option available. In others, it makes sense because it allows far better performance — albeit in an older airframe — for far less than it would cost to get similar performance in a new aircraft. But across the board, owners who choose a conversion do it for some combination of three basic factors: horsepower, efficiency and improved maintenance costs.

Cash-Back Conversion? A turbine engine conversion is a significant investment. So in trying to figure out if it is worth it, it's only natural to wonder how much more your new-and-improved airplane will sell for with its new-and-improved engines.And the answer is … it depends. Almost everyone agrees that if you sell it immediately, you'll pretty much get your investment back. If you keep it and fly it for a while, the value of that conversion will start to decrease "very shortly," says Fletcher Aldridge, publisher of Vref Aircraft Value Reference. But there are exceptions to both of those rules.The exceptions and caveats exist partly because, as Jay Mesinger, CEO of J. Mesinger Corporate Jet Sales, puts it, "we don't have a sophisticated analytic process to establish modification value for resale." In real terms, that means modifications are worth different things to different people at different times.If a buyer has a need for a specific type of modification, a seller can do well. On the other hand, in a down market like the present, Mesinger says owners may get only "10 to 15 percent of the value of the modification, or nothing at all." In some cases, the only difference might be that a modified airplane sells, when an unmodified airplane sitting next to it doesn't."It's like adding a swimming pool to your house," Mesinger says. "It's hard to say how much value it adds. So if you're going to put one in, it should be for your own enjoyment, not simply to increase the value of the house."On the other hand, there are times when an engine conversion can significantly increase an aircraft's value -- like if the modification gives the airplane a kind of performance no other aircraft, new or used, can match.The numbers also depend on how much the converted aircraft is used. "I agree with Jay [Mesinger] that if someone only flies 100 to 200 hours a year, they will never be able to substantiate the savings," says Bobby Bishop of Texas Turbine. "But a commercial operator who flies 500 or 1,000 hours a year can get back the cost."Time and market exposure also play a role. The value of a conversion can go up if so many aircraft in that class opt for it that the change becomes "a de facto standard," says Steve Gomez of Honeywell. "Then, if you go to sell the aircraft, if you haven't done the mod, the value will go down by that amount." By the same token, once aircraft owners see enough examples of a conversion flying without problems, the desirability of the mod is likely to go up.And while no sale is easy in a tight economy, tough times tend to make an older-model aircraft with upgraded engines look better."Today," Mesinger says, "because there's no broad-based lending available, people have to enter aviation very carefully. Two years ago, people were pooh-poohing aging airframes. But today, more and more people are buying older aircraft, and that gives some of the modifications a boost."

Everyone involved with conversions also agrees that they've become more popular in recent years. In part, that may be a result of having more modified aircraft in the fleet, allowing owners a greater comfort with the whole idea. Another factor may be stricter FAA requirements enacted in 2001 that now require any after-market modification shop to certify any mod not just to the original certification standard for a particular aircraft, but also to the latest amendment level. Still, Bishop recommends that owners contemplating an engine conversion should do their homework before buying.

"Find out how long a shop has been around, and how many aircraft that they've modified are in service," he says. "Ask for a list of customers you can contact, and then try to find some that aren't on that list. Spend a lot of time talking to the company first. If they blow you off at that stage, you're not likely to get good product support after that fact."

Above all, Bishop says, with an investment that big, look at all the possibilities.

"Don't just do it because Billy Bob did it," he says. "You'd be surprised at how often that happens."