Clifford Development expects STC approval this month for its re-engined version of the Citation II. Certification of the S-II should follow within about 30 days.

Both STCs replace the airplane’s original Pratt & Whitney Canada JT15D engines with the fadec-controlled Williams FJ44-3A. The 3,000-pound-thrust Williams engine (derated to 2,820 pounds) is the same one currently in use on the CJ3, and it gives the older Citation improved performance and lower fuel burn.

Jim Clifford, CEO of the Toledo, Ohio-based company, has more than 30 years’ experience in after-market aircraft support, is a pilot, A&P and IA, and is a former senior vice president of Kal-Aero. While at Kal-Aero Clifford gained substantial experience with Cessna Citations, which is why he opted to make the Citation II his company’s first STC project. “I knew we could significantly enhance the aircraft’s performance, so our first STC project was the Citation II [550],” he told AIN.

“The straight II is similar to the S-II except for the wing. The S-II wing is essentially a Citation V wing, so it performs better than the straight II, making the S-II a logical next STC project.” The company hopes to have both aircraft ready at the same time so the FAA can go from one test flight to the next.

“The experience with the straight II carried over when we started work on the S-II last February. The aircraft had its first flight on July 18. The time to climb to 43,000 feet is 27 minutes and it cruises at 415 knots; the standard factory model takes 107 minutes to climb to FL430 and its cruise speed is 370 knots.”

The flight profile was designed to evaluate aircraft handling and engine controllability. The company also conducted a second flight, which evaluated all interfaced systems and the aircraft’s response to the new, more powerful engines.“These flights are a continuation of the successes that we have had at each milestone with this airplane,” Clifford said. “The first power-on went well; the first engine runs were flawless. Each engine-interfaced system, including pressurization, was evaluated and the airplane returned without a single squawk.”

According to Clifford, the modification provides a 25-percent faster long-range cruise speed, 40-percent better NBAA IFR range with four passengers, a 10-percent reduction in takeoff field length, 13 percent more thrust and 28-percent lower fuel burn.

“This is a good market. There are 155 aircraft in operation, with 74 percent of them in North America and 11 percent in Latin and South America,” Clifford said. “The next highest concentration is nine percent in Europe, two percent each in Asia and Africa and one percent in Australia.”

Clifford said the STC is more than just hanging an engine on the airframe.

“From the beginning we asked what we could do to marry the new engine to the systems to make it a better aircraft. We came up with about 30 different things. For example, corrosion problems in the old generator installation wires and ground points resulted in splits [uneven amp loads out of the generators]. We solved that problem by putting in copper wire and ran the ground directly to the battery rather than grounding it to the engine pylon.”

The STC also includes a change to the fuel and hydraulic fittings. “Fuel and hydraulic lines have always had identical fittings, making them easy to cross connect accidentally,” Clifford said. “We left one as an AN fitting and made the other an MS fitting so it’s no longer possible to make that mistake.”

Another small but significant change is in the bleed-air system. The original aircraft had a peri-seal, essentially a large silicon O-ring, which tended to break. The STC changes them all to sealed bellow assemblies so the pipes can move and absorb vibration but the seals won’t crack.

According to Clifford, the STC also includes winglets that lower fuel consumption in cruise and yield a 5- to 7-percent performance increase.

“We made the improvements using available Cessna parts and products, partially to make Cessna comfortable with what we were doing but also so the operator can call either Clifford or Cessna to get parts. Our STCs have both part numbers.”

The cost of the conversion, including winglets, is $2.28 million. Engine installation does not require any structural modifications and uses the existing factory engine beams. There is a core credit included for the P&WC engines, but if there is more than 500 hours of remaining life before scheduled overhaul, that will be taken into consideration.