The Cessna 441 and 425 Conquest turboprops have been among the hottest turbine airplanes on the used market for several years. Both the higher flying, bigger and faster 441 Conquest II and the smaller PT6-powered 425 Conquest I have been selling for near their new prices, even though they are 23 or more years old.
The reason for the popularity is that both turboprops deliver excellent performance with great fuel economy and easy to fly manners. In other words, they are exactly what the owner-pilot wants. And the Garrett TPE331-powered Conquest II can cruise faster than 300 knots with an IFR range of more than 1,500 nm in still air. That means it can fly that 1,000 nm trip upwind that so many owner-pilots want to make routinely.
An issue with the Conquests is, well, their age. A crack was discovered in a critical structure in a 441 in Australia a few years ago that raised awareness of the need for extra attention. And then the FAA launched its "aging aircraft" program that prompted all manufacturers of turbine-powered airplanes to examine their fleets and establish inspection stand-ards that would ensure the airplanes remain airworthy as the years and flying hours roll by.
Cessna examined the history of service bulletins issued to correct problems discovered in the fleet over the years, and also the list of service difficulty reports filed by shops who discovered unexpected wear or failures during inspections. Fatigue and damage tolerance analysis was conducted, and mathematical models were built. Cessna then used actual load testing to prove the models' accuracy. With this information, plus results from original static and fatigue cycle tests, Cessna was able to define a program that would identify critical areas of the airframe structure that could be subject to fatigue and corrosion and required more than the original inspection attention.
What followed is a supplemental inspection document (SID) issued for both Conquest models in 2007 with an effective date of September of last year. The SID added about 20 new phases to the required inspection program on the airplanes. It is an expensive program, and very intensive, but it is what the FAA and Cessna believe is necessary to ensure the Conquests have the same airframe integrity that was originally certified.
Among the groups that had significant input into development of the Conquest SID program was Yingling Aviation, based on Wichita's Mid-Continent Airport across the runway from Cessna's main plant and headquarters. Yingling has been a Cessna dealer, service center and major parts supplier since 1946, believed to be the longest operating dealer in Cessna history.
Because of its physical proximity and long-term relationship with Cessna, Yingling provided input on its experience in maintaining Conquest turboprops, and was among the first to begin performing the inspections once the documents were issued. Yingling has conducted about one-third of all SID inspections so far and is the most active and capable Conquest service center in the world.
Initially Conquest owners were shocked by the scope of the SID program. If all phases of the inspection are completed at once, which is not required, the inspection alone required more than 940 shop hours at Yingling. And then there is the additional cost of repairing any problems that are uncovered. Some wondered whether the Conquest was doomed by such a large required maintenance event. But as owners have come to understand the reasons for the SID program, and to consider that it requires careful inspection of critical components that have not been seen since the airplane was assembled as long as 30 years ago, it starts to make sense.