Costs of Developing an STC

There’s an old saying that goes: "The more things change, the more they stay the same." Well, that adage certainly does not apply to earning an FAA supplemental type certificate (STC) in today’s world.

"We lovingly say that what we were able to do with a simple logbook entry 15 years ago became a field approval 10 years ago, and five years ago became an STC," explains Jim Clifford, president & CEO of Clifford Development.

Clifford’s case-in-point is the process his company recently went through to earn FAA unrestricted STCs to upgrade legacy 550 and S550-series Cessna Citations with state-of-the-art Williams Intl FJ44-3A engines with full authority digital engine control (FADEC). This is the first STC to cover both popular Citation aircraft and was issued with no operational limitations or restrictions.

And while is may seem relatively simple to hang a pair of Williams engines on the 550 and S550, the process became a learning experience for everyone involved.

More Than Just the Engines

"We’ve been involved with Citations since the early 70’s," Clifford says. "I spent 18 years at Kal-Aero before Duncan bought us. We were the largest independent Citation Service Center in the world. We’ve learned a lot about the Citations over the years and like any legacy airplane, systems and components have gotten a lot better — more efficient engines and equipment and components that were originally designed one way and changed for the better on later model airplanes."

The availability of "more efficient engines and equipment" was the seed for Clifford’s most recent project. By replacing the original JT15’s with the FADEC-controlled Williams FJ44-3A’s, Clifford’s team was able to increase the available thrust by 20 percent, while cutting fuel use by 35 percent. According to the company, that netted a 50 percent increase in NBAA range with four passengers and a much quicker climb to FL430. "That’s a tremendous advantage in these economic times, especially if fuel prices rise again," Clifford says.

But this was more than an engine transplant. Clifford’s team took the opportunity to include some 35 other operational and maintenance improvements to the venerable 550 (Citation II) and S550 (Citation SII), some of which were already STC’d by other companies. The list of enhancements includes a new Ametek digital engine display, heavy-duty BF Goodrich brakes, Hawker 44ah battery, improved starter/generator cooling, improved instrument panel cooling, and the removal of the thrust reversers. All total, the Clifford enhancements cut 250 lbs from the empty weight.

"We married new Williams technology and some other product improvements that have come about in the new CJ3 and Citation V series to create a more efficient, more reliable aircraft," Clifford says. "With its 35 percent reduction in average trip fuel consumption and noise reduction greater than Stage 4 standards, this STC transformation vaults the eight-passenger 550 and S550 into a completely new jet category."

An Old Game With New Rules

While the combined experience of Clifford and his team at Great Lakes Aviation includes obtaining over 3,000 FAA STCs, including nine engine replacement STCs, the bolting of the FJ44-3A’s on the 550 and S550 was something just a bit different — this was the first time these Williams engines had been installed on a Part 25 airplane.

"Everything below 12,500 pounds is a Part 23 airplane and those above are Part 25 airplanes," Clifford points out. "Basically, the certification requirements for a Part 25 airplane are greater in a number of areas. There was some new ground to cover for both the Clifford Development team and the FAA on this."

"I’m not sure that from a form, fit and function aspect we do it any better than we did 15 years ago, but what has changed dramatically in the industry is the requirement for documentation and also the level of testing required to substantiate your basic assumptions," Clifford continues. "This was new territory for us. I have to say, the experience with the Chicago office of the FAA was professional, friendly and very helpful, while assuring compliance with every aspect of the federal regulations."

"What we see with the FAA is new technology flooding the market at an incredible rate and the testing and approval requirements for the first approvals are tough but they get a lot easier as the technology is proven," he says.

"Like anything else, when you are on the front side of technology it requires that you spend more time and money to figure these things out."

"Five years from now when we all know it [technology] and it proves to be perfectly safe and has no adverse failures the certification process will probably become relatively easy," Clifford adds.

Clifford explains that the biggest challenge to everyone involved was the integration of new FADEC electronics technology with current FAR requirements into a legacy airplane — in this case it was the first marriage of the new-generation digital Williams engines with the Citation’s analog airframe.

"It’s like trying to couple a new-generation digital autopilot into an analog airplane’s systems," he explains. "You can’t just plug in the digital controller. You have the same problem with marrying a legacy analog airplane to a state-of-the-art digital FADEC engine. Most of the things produced by the airframe are done in analog and they need to be converted to digital."

"You end up designing software and hardware that actually creates a ‘happy box’ to convert the signals for you," Clifford says. "It creates a bit of a design and engineering challenge to make all that stuff work at a higher level. It’s perfectly doable, it just takes more time and, of course, more dollars." Clifford adds that "this was new ground for us, Williams and the FAA. One of the biggest problems was the P2/T2 sensing system. It wasn’t at Part 25 levels so it required a redesign to a higher safety standard and it also required a rewrite of the Williams FADEC software."

Adhering to strict new High Intensity Radiated Fields (HIRF) requirements was another area that needed considerable attention.

"The requirements for HIRF in a FADEC airplane’s engine instrument display is far greater than in a normal [analog] system, because it interfaces with the FADEC. A FADEC system has to meet all those HIRF requirements, plus its software and related interfaces have to be certified to Level A equivalent to RVSM," Clifford says. "Nobody had thought about the requirements for FADEC approval when we went into this because the engine basically was already certified."

One Step Forward, Two Back

Another thing that no one thought about was the possibility that a major sub-system supplier could lose a lawsuit and not be able to supply a critical part. But I’m getting ahead of myself...

As Clifford explains it, one of the requirements of putting FADEC engines on a legacy airframe is that the system needs air data inputs that are equivalent to those required on an RVSM-approved system. To save time and money, the company decided to use an "off-the-shelf air data solution" modified to do the required digital-to-analog and analog-to-digital signal conversions.

"We started with a Kollsman product and added the other conversion and testing capabilities to it," Clifford says. "We had flown the airplane and collected the preliminary data back in the middle of 2007. Kollsman was supposed to deliver a TSO’d box in December of that year — and they did. We have two of them. Unfortunately, at the same time they were in a legal dispute with IS&S that few people in our industry knew about."

"The outcome of the suit was that Kollsman could not produce any technology or products related to that litigation. That meant they would not be able to continue to produce the box that was already flying on our airplane," he continues. "All the data we had collected up to that time was useless. We pretty much had to start over."

As it turned out, the folks at IS&S actually provided the solution. "Putting aside that they had a legal problem with the original supplier, they [IS&S] were very good about the whole issue," Clifford says. "They stepped up and produced a new box and got it certified for us in record time. That’s the solution we’re currently using on the airplane and it’s working very well."

"I would have loved to have the STC out before the current economic downturn, but I understand the situation. There’s a lot to the story, but from our perspective, the IS&S team stepped up and tried to help us as much as possible," he added. "In the end, we got what we needed and we’re on to it. Aviation stories always have these little sidebars."

According to Clifford this "little sidebar" to their story delayed them about 11 months and cost an extra $1.8 million (not to mention any potential pre-downturn sales they lost), but that’s the STC biz.

"If you take out the added cost of the air data dilemma, we’re probably about 25 percent over what we had originally budgeted for the Citation 550," Clifford explains. "That’s well within boundaries. If you don’t go in expecting to go 25- or 30 percent over budget, then you’re in trouble. We were pretty good."

Where they turned out even better was with the S550 project. "We actually started cutting metal on the SII (S550) in February of last year. We had a flyable airplane in August," he says. "The development cycle on the SII was significantly shorter. Obviously, all the interface challenges were taken care of with the straight II (550) development."

"The SII actually came in about 25 percent under budget," Clifford continues. "We obviously thought it would be cheaper simply because some of the design and engineering was already done. It is still a Citation so developing a second product on the type there were some lessons learned — and actually it went smoother than we thought."

Opportunity Knocks

While the project did meet with more turbulence than Clifford and his team could have foreseen, the end result meets all of their and customer expectations. "This certification comes at a time when increased operating efficiencies and reduced environmental footprints are paramount."

"The list of improvements will be important to every operator," Clifford added. "But the performance truly stands out. Of the dozens of pilots who have flow this airplane, each has raved about the performance. When they walk away from the airplane after their flight, they have a smile from ear-to-ear. This modification provides new life to an aircraft beloved by all of its operators."

Of course, that’s the goal of every STC project — to make something that’s already good that much better. Clifford said that there are other improvements yet to be made to the Citations and other popular aircraft models. In fact, with the ink barely dry on these STC’s, the process is almost complete at Great Lakes Aviation to earn yet another approval to enable Williams’ engine information to be displayed on the Rockwell Collins Pro Line 21 IDS system in the 550 and S550 aircraft.

What tips does Clifford have for other aspiring STC developers? "First do your homework — both with respect to the hardware under consideration for modification and the applicable FARs. Then engage the appropriate engineering, DER (designated engineering representative (DER) and FAA office early on," he says. "And by all means, be open and forthcoming with them. Open and honest communication will reduce interface time and speed up your STC approval."