Buying A Used Aircraft: Cessna Conquest I

For those with the skill and budget, a Cessna 425 Conquest I may still be one of the least expensive ways to get into the world of turboprop twins. Its direct competitors might be the Piper Cheyenne I, a Beech King Air 90 and even some turboprop singles. And for those with a goal of eventually landing in the left seat of a Citation jet, the Conquest I is a logical primer. But don’t expect cheap maintenance or insurance and do plan on extensive training. Welcome to the turbine world.

Confusingly, the Model 425—eventually dubbed Conquest I—earned its type certificate almost three full years later than the model 441 and started life as the Cessna Corsair. An evolution of the successful Cessna 421 piston twin, the 425 was powered by venerable Pratt & Whitney Canada PT6A-112 engines. Before production of Cessna’s “baby turboprop” ended in 1986—along with a lot of other models from other GA manufacturers—some 236 Model 425 Corsair/Conquest Is were produced.

The Conquest is not a model 421 with PT6As—not by any stretch. The 425 is its own airplane, even though a handful of Continental GSIO-520N-powered Cessna 421 Golden Eagles have the Riley 421 Prop Jet conversion. There are a number of distinctions, and very different systems were installed in the Conquest. Plus, the aft fuselage structure is much beefier than that of the 421, evident by the rivet count when comparing the airplanes side-by-side.

One of the elemental strengths of the 425’s design is the nearly bulletproof Pratt & Whitney Canada PT6 free turbine engine. The A-112 version originally installed in the 425 is a fairly unsophisticated one that is not highly stressed. It is flat rated at 450 SHP and overhaul will be every bit of $400,000 at the 3500-hour mark. For pilots transitioning to turbine power and for operators at smaller airports, PT6 power is the proven right choice and is easy to support. But, you’ll still need to thoroughly understand how to and how not to operate these engines or you’ll pay dearly on the shop floor.

At its introduction as the Corsair, the 425 had a maximum takeoff weight of 8200 pounds and a basic empty weight of 4870. Full usable fuel weight of 2452 pounds (366 gallons) and average optional equipment weight of 375 pounds left a pretty miserly 503-pound payload. The maximum takeoff weight was increased to 8600 pounds in 1983 and the basic empty weight increased by 52 pounds, leaving most of the increase for payload. At the same time, the 425 was formally inducted into the “Cessna Propjet” family and was renamed the Conquest I.

Earlier 425s could be modified to the new weights quite easily, and most all have been. Zero-fuel weight increased from 6740 to 7000 pounds; maximum landing weight remains 8000 pounds. While the 425 does not have the payload capacity of a C90 King Air, it is nearly a fill-the-seats airplane. With lots of lard and luggage toward the rear of the airplane, CG has to be checked carefully, but the loading range is quite wide. The Conquest is a good family and business traveler. The average 425 can seat eight: two in the cockpit, four in club seats, and two in the additional full seat on the left rear side of the cabin and belted potty seat. Even with the maximum number of seats, there is a generous baggage area in the aft cabin (about 30 cubic feet and up to 500 pounds). The cavernous nose houses another 22.4 cubic feet of baggage area with a maximum load of 400 pounds. It’s a big airplane. 

But, there is a lot of cubic space in both the cabin and baggage areas that could tempt those lacking caution and experience to exceed load limits. Yield not to that temptation. Aside from CG concerns, exceeding maximum loads can cause serious performance deterioration, especially in high density altitude conditions. You don’t want to go there with this airplane.

With sea-level, standard-temperature conditions and gross weight the (well-flown) 425 can clear a 50-foot obstacle after a run of 2420 feet and land over the same barrier in 2120 feet. With the accelerate/stop and accelerate/go distances of 3800 and 3360 feet, a properly qualified pilot can safely operate from 4000-foot runways with room to spare. If you are used to flying a Skyhawk or a Cherokee, that may sound like a lot of runway. For a nearly 9000-pound airplane, however, that’s pretty good.  

Off the ground, the 425 operates best between FL230 and 280. While maximum speed of 260 knots comes at 18,000 feet, fuel burn is high. At FL260, max cruise power produces 251 knots and 1240-NM still-air range. In the mid-20s, the 425 is a five-hour-plus-reserves airplane. With a maximum operating speed of 230 KIAS and max gear operating of 175 and approach flaps of 174, the 425 can return to pattern altitude quite quickly when necessary. Like we said—manageable for pilots stepping into the world of twin turbines.

You’ll find many 425s with upgraded avionics, but some still sport original Collins gear. Look hard at the performance of original autopilots, including the optional Sperry (and later Honeywell) SPZ-500 flight control system. Even for its $75,000 cost at the time, it was a big improvement over the ARC (Cessna) 1000 FCS, which has been one of the weak links in the 425 and other Cessna twins. Some 425s were equipped with the ARC 800 series autopilot, which is even less desirable than the 1000. Still, these are aging systems that can be expensive to maintain.

If you find one with Collins or ARC avionics, we would budget $100,000 to start for a full-up avionics retrofit, and likely more if you replace the autopilot. Common upgrades include the Garmin G600 TXi primary flight display, S-TEC digital autopilot and Garmin GTN navigators. Don’t forget ADS-B transponders—some airplanes sourced overseas might not be equipped. It may be time for some panel work, anyway. As a requirement for British certification, a master caution warning system was added. This is a useful addition because the annunciator panel can be hard to see in direct sunlight, even though it is mounted at the top of the panel, under the glareshield. 

Still, a noticeable improvement was made in the later run of 425s: better interior design, fit and finish. Appearance, comfort and durability all were improved. Redesigned cabinetry also provided more legroom for passengers in the principal four club chairs. Passengers and pilots generally like the Conquest for comfort. A Conquest with well-balanced rotating components and a fully functioning propeller synchrophaser can be relatively quiet and comfortable at cruise power settings, especially at propeller RPM of less than 1900. Each airplane has an ideal, low-vibration RPM that can be determined with practice. Good propeller balancing makes it even better.

A factory option made available in 1982 was Cessna’s Cescom maintenance program, which was turned over to CAMP Systems. A genuine programmed maintenance scheme in its later form, Cescom provided more flexible inspection options that could reduce total hours and cost for those who scrupulously followed the recording and reporting requirements. A service life recorded on Cescom would be a strong plus for any used 425. So would one that’s been cared for; the best Conquest I is one fully up to date on hourly, cycle and calendar maintenance, ADs, service bulletins and kits, product improvements, updated electrics, current avionics and a sound pressurization and climate control system. Make no mistake, these are complex machines that require a solid maintenance effort with little tolerance for deferring squawks.

And, don’t be deceived by pigs in lipstick. The best-looking Conquest I with the newest interior and latest paint job might be appealing, but they are the least important part of any airplane purchase, especially something as complex as a Conquest. There are many buyers who were lured by good looks thinking the airplane was good to go, only to find they had bought hangar queens. Moreover, selecting the wrong shop can be as expensive as neglecting proper maintenance altogether. The best approach is to talk to other Conquest I operators to get their recommended service and information sources.

Keep meticulous records, too. Get involved in an information-sharing network of operators and service/support organizations. It can serve as effective early warning and help keep operational readiness up and costs down. Cessna service centers specializing in 400-series twins also can be a good source of research materials for determining what the proper maintenance status of a 425 should be.

With all that in mind, we think any serious Conquest I buyer and owner should absolutely join the Twin Cessna Flyer organization (www.twincessna.org). 

We dug into Cessna 425 accident reports back through 1985 trying to find 100 so that we might do some meaningful analysis into problem areas with the fleet, but only found a grand total of 27 mishaps of widely varying severity. Of five accidents in IMC, three involved pilots who lost control of their airplanes and postmortem exams found significant levels of disqualifying prescription drugs in their bloodstreams. Another pilot broke out of clouds on an ILS at 100 feet in a left turn, which he continued until ground impact. A pilot who had his passenger crouch beside him to “help find the runway” on an ILS went well below minimums before missing the approach. Rather than climbing, he then flew level into obstructions. The passenger survived. The pilot, who was not wearing his shoulder harness, did not. Our advice is to bring your A-game to the cockpit, source the best training you can find and get an insurance quote before even considering a Conquest—or any turbine.

We think the 425 probably is the simplest of all the twin turboprops to transition to. Thus the nickname “baby carriage.” Pilots transitioning from light twins will have to get a feel for control pressures, trim use, aircraft performance and weight (inertia). But good training and a bit of experience quickly lead to confidence. Engine management, from startup to shutdown, is as important as how well you can fly (or program it to fly) a busy approach in the clag. And you better mind those PT6As. Poor power management can lead to premature failure or, at the least, much higher hot-section inspection and overhaul costs. Hold onto your wallet. 

The good news is the Conquest is not an orphan. Despite the fact no 425s have been produced for a few decades, operators tell us that Textron/Cessna support is commendable, particularly when compared to most other manufacturers or former manufacturers. That makes the airplane (good ones) desirable on the current market.

Our Fall 2022 Aircraft Bluebook shows the average retail of a 1983 Conquest I at $775,000, although asking prices for ones with refurbs and improvements are well over $900,000. The respected Controller.com virtual marketplace was listing a 1981 Cessna 425 for $1.45 million. It had the latest Garmin avionics, speedbrakes and low-time engines. Airplanes like these should be turnkey, or at least as turnkey as a complex twin turboprop can be.

“We’re sold on the Conquest being an easy turbine upgrade from the Cessna 421. It was a very easy transition as so much felt very familiar, and because so much of the airframe and the cockpit is similar. I’ve heard that Cessna upped the build quality, but we haven’t really noticed much between the two. The difference between the Conquest and the Citation, however, is significant and it is clear that the Citation 501 from the same era is built to a much higher standard in all respects,” owner Stuart Clumpas told us.

Our thanks to Stuart for helping by sending some photos of his good-looking Conquest (wearing a Scheme Designers paint scheme) for this report, and the ones in the full report (which includes market comparisons and a full NTSB safety summary) on the Cessna 425 Conquest I in the Used Aircraft Guide over at sister publication Aviation Consumer magazine.