Depressed used aircraft values have stalled sales of some re-engine programs, but their providers insist that they remain good values because of the dramatic increases in aircraft efficiency and performance they provide.

"We're seeing a different kind of customer now," said Clifford Development's Alden Andre. "Before we'd see a customer who wanted a turn-key solution. They wanted us to go out and find a used airplane and then convert it. Now we are seeing more customers who are bringing their own airplanes to us."

While Andre said he expects turn-key business to improve with the economy, he said that right now those customers are concerned about depressed resale values.

Like most re-engine programs, Clifford's focuses on re-engining a popular legacy aircraft with Williams International FJ44 turbofans with average costs in the $2 million to $2.3 million range depending on the value of the engines to be replaced.

Clifford's program replaces the stock Pratt & Whitney Canada JTD15-4 engines on the Citation II with a pair of Williams FJ44-3As equipped with dual Fadec. The conversion also includes 35 other changes to the aircraft as part of the STC installation, including digital engine display and heavy duty brakes. It reduces empty weight by 250 pounds, average trip fuel consumption by 35 percent, noise to Stage 4 standards and time to climb to FL430 to 27 minutes. Range increases by 50 percent and maximum cruise speed increases by 15 percent.

This range of performance improvement is typical for re-engine programs currently available for the Citation I and II, Learjet 25, Falcon 50 and the Beechjet from a variety of providers including Clifford, Sierra Industries, Spirit Wing Aviation, West Star, and most recently Nextant Aerospace on the Beechjet. However, since the end of 2008, prices for those airplanes, already depressed, have dropped another 30 to 35 percent on average. A 1983 Learjet 25 is only fetching $440,000, and many other of the aforementioned models can easily be had for less than $1 million on the open market currently according to the aviation price tracking and valuation service Vref. As many of these airplanes are at least 25 years old, buyers will have a hard time finding financing for the aircraft, the conversion or both. However, even in this down market, re-engining still makes sense for some aircraft, according to Vref's Fletcher Aldredge.

"These programs still make sense if someone needs the speed and capabilities" these re-engining programs offer, Aldredge said. "Now, will you get your money back [when you resell the airplane]? Probably not, at least not 100 percent certainly."

Aldredge said historically this has always been the case in good times and bad on a wide variety of aircraft upgrades, not just engines. "We've dealt with this issue for decades. Will you get your money back on a four-blade prop on a King Air? No, but it sure looks cool and if you think it makes [the cabin] quieter, that's great. You can buy a fancy EFIS panel, and there is nothing cooler than that, but are you going to get your money back on that? Never."

Aldredge said that customers who are attached to their airplanes "have to do an engine overhaul anyway" at some point, and often it makes sense to hold onto the airplane while adding engine upgrades. "Their pilots are typed, their mechanics are checked out, the airplane fits their needs and it works really well. If they don't put a pencil to it too hard it really makes a lot of sense for those people." But Aldredge cautions that people who think they are going to increase the resale value of their aircraft anywhere near the cost of an engine upgrade are deluding themselves. "Those few people who go out there and say that they are going to increase the value of their airplane by $2 million—well that's not going to happen."

However, some of these conversion packages can be real game changers for operators of older aircraft. Spirit Aviation's SpiritWing conversion for the Learjet 25D yielded a noise reduction to Stage 3, halved fuel burn, and boosted range. With four passengers, range increased from 1,100 to 1,700 nm over the stock airplane.

Sierra Industries's Citation I packages also yield this category of improvements. The stock airplane barely cruises above 300 knots for long range cruise and has a range of 970 miles with four passengers; payload with full fuel is just 820 pounds. The engines have a TBO of 3,500 hours and cost more than $350,000 to overhaul. However, first-generation Citations have no airframe life limit. Properly maintained, they will fly virtually forever. This, combined with their relatively low price, generally under $900,000, makes them attractive candidates for modification.

For $1.6 million to $1.8 million–the price varies depending on the trade-in credit for existing engines and the upgrade package selected–Sierra offers a modification that includes the more powerful and fuel-efficient Williams FJ44 engines, auxiliary fuel tanks and a modified wing. This can make these older Citations fly higher, faster and farther than any new very light jet and for less money.

Sierra has converted about 175 Citation Is with its Eagle II and Stallion packages and the performance changes can be large. Eagle II flies 54 knots faster and can climb directly to 43,000 feet, 2,000 feet higher than the Citation I. It gets there a lot faster, too. A straight Citation I climbs with both engines at 2,719 fpm; the Eagle II climbs 4,500 fpm. An Eagle II will reach 43,000 feet in 25 minutes, while a straight Citation I must step climb to 41,000 feet over the course of 80 minutes. Takeoff and landing distances shrink, too, allowing the Eagle II to operate out of 3,000-foot strips. Range increases to 1,400 nm in the Stallion (four passengers, one pilot and IFR reserves) and to 1,650 in the Eagle II. The Stallion can also be fitted with Sierra's new fuselage auxiliary tank, which boosts range to 1,750 nm. At cruise altitude, an Eagle II delivers 35 percent more thrust and burns 40 percent less fuel than a straight Citation I. The Williams engines are also quieter than the original Pratt & Whitneys, which helps cut cabin noise.

The decision to upgrade was not difficult for Bill Hettinger, who owned a stock Citation I and looked at VLJs and the Citation CJ2 before picking up a 1980 Citation I with an Eagle II conversion. "None of the VLJs had the range and the CJ2 was more expensive," Hettinger said. "This airplane is a known quantity–it was not a leap of faith."