Blackhawk News

November 1, 2022

The Amazing Cessna 425 Conquest I

By Jim Allmon, President & CEO Blackhawk Aerospace

We all have our favorite airplane that we’ve loved since the first time we sat in one. I personally have three: the trailing link gear Cessna 421C, the Shrike 500S Twin Commander, and the Cessna Con­quest I. Each has its own special appeal, but the Con­quest I is just a very special airplane in my book.

I started my flying career in the 500 series Twin Com­manders back in the early ’80s and loved the simplicity and toughness of the airplane. I eventually moved up through the Twin Cessna ranks into the Citations, King Airs, Cheyennes, and Learjets; but from the first time I flew in a Conquest, she has always held my heart over all the others.

My first flight in a brand-new Cessna Corsair, later to be renamed the Conquest I, happened back in 1984 if memory serves. I was a young pilot with around 900 hours in my logbook. I was a demo and delivery pilot for a local aircraft dealer in Tulsa, OK, when I was given a demo flight in a brand-new Corsair. I was in awe as soon as I settled into the co-pilot seat. The smell and feel of that new airplane was intoxicating. No old aluminum, oil, and musty leather smell that I had grown used to in the old 310s and Commanders that I had been flying. It’s like a new car smell, only a lot more expensive. It was just the sweetest, easiest, most forgiving airplane I had ever flown then or since. What’s not to love? Huge nose baggage, wide oval cabin, auto-feather system, quiet in cruise, faster than the 90 series King Airs by a good 15- 20 knots, easy to ingress and egress the cockpit with no pedestal to climb over, trailing link landing gear that makes any pilot look like a pro, good single engine per­formance, the list goes on and on. Passengers love the quiet cabin with the slow turning PT6A-112 engines that allows them to have a conversation in the back without headsets.

The 5.0 cabin psi differential pressurization is a very simple system compared to the King Air C90. The flow packs seem to last longer than the C90 packs and are so simple to operate – one knob – off, left, right, and both. One of the things that you need to watch on the Conquest is making sure that the oil door is latched down properly. If they aren’t, they can pop open in flight and depart the airplane. Those doors are about $900-$1,200 if you can find one.

The other issue is inboard wing wrinkling. Most people think it is from a hard land­ing. It is actually caused by turning while taxiing with one brake locked, usually the left. The design of the trailing link land­ing gear and the distance from the fuse­lage puts sort of an awkward bind on the bracing in the wing root area if the wheel is not turning when the airplane is turn­ing. This can wrinkle it in one instance or over time. You will see that wrinkle on about half of the airplanes out there. You can replace the skin, but the wrinkle will come back the next time you stand on the brake to turn.


Then you have the SIDs (Supplemental Inspection Documents). I could spend the entire article on SIDs, but that is best left to the experts at Yingling or Technic Air in Fresno. The first time you do the SIDs (most of the initial SIDs have been complied with by now), it requires removal of the engines, wings, tail, boots, just about everything. This is basically an inspection program put out by Cessna to maintain the structural integrity of the aircraft, to address corrosion, to develop maintenance program guidelines, to detect fatigue cracking, and to assess damage-tolerance of structural repairs. If your plane or one that you are considering buying has been through the initial SIDs at one of the major Conquest shops, you are a lot better off. There are recurring SIDs after the first one, but they aren’t as onerous. Make sure you know where the SIDs were done and what the status of the recurring SIDs are before you buy.

Downfall of the Turboprops

Unfortunately, in 1985-1986, the twin turboprop world ground to a halt for most models. With skyrocketing product liability insurance costs and the country be­ing in the middle of the worst recession since the Great Depression, many OEMs, includ­ing Cessna, stopped building twin engine turboprop aircraft. Some went to jets only, others got out altogether. It was during this tu­multuous time that Cessna was sold to General Dynamics, enabling the company to overcome the mounting product liability insurance premi­ums that were topping $35 million a year. This event saved Cessna as General Dynamics infused cash into the company, but also had the financial capability to self-insure, saving Cessna millions a year. Un­fortunately, there was a price to pay: With Russ Meyer at the helm, Cessna made the decision to realign the focus of the company to the more profitable Citation jet product line. Until the recent Sky Courier came along, this decision doomed the twin turboprops at Cessna forever.

In 1986, the last of the Conquest series 425 and 441s rolled off the assembly line in Wichita. Only the vener­able Beechcraft King Air and the Piper Cheyenne 400 soldiered on as most other turboprops also ceased pro­duction in 1986. Piper ended its production of the Chey­enne 400 in 1993, and to make sure they stayed out of that market, Piper destroyed all tooling used to build the Cheyenne series aircraft. It was the end of an era.

When production ceased on the Conquest I, 236 aircraft had been built. Most are still out there flying today. Lit­tle was changed on the airplane from 1981 through 1986 other than some avionics upgrades, but no one created any major STCs (Supplemental Type Certificates) for the airplane due to the small number of aircraft. It would remain unchanged for 14 years when a little-known startup company called Blackhawk Modifications came on the scene and gave the Cessna 425 a whole new lease on life.

An Idea

The idea of doing an STC on turboprops had been float­ing around in my head since I had worked at RAM in the early to mid-’90s: Why don’t we do the same thing that RAM had been doing for decades on piston aircraft, but do it on turboprops? The main difference: We would buy new engines off the shelf from Pratt and Whitney at a higher rated horsepower instead of modifying the engines as RAM does with Continental piston engines. The Conquest wasn’t my first or even second choice as I had once flown a King Air “Taurus” mod that Ed Swear­ingen of Swearingen Aircraft fame had certified in the mid-’70s and was impressed with the performance on it.

Ed had replaced the PT6A-21 and -28 engines with a PT6A-135 engine that he talked Pratt into building. They took two different engines and morphed together a larg­er compressor with a slower turning gearbox to make a “Century Series” engine. All Century Series small en­gines {112/114A/140A/135/135A) have a 1900 RPM prop speed. How Ed Swearingen got Pratt to do that is a mys­tery, but that story was told to me directly by Ed himself. Pratt eventually pitched the -135 engine to Beech several years later, and it ended up on the new King Air F90.

The idea that I originally had in mind was for a King Air engine upgrade since there were so many King Airs out there. I had no idea how to get the project off the ground, so I mentally filed it under “dreams that may never come true” and left it there. But it could work, couldn’t it?

A New Beginning

While I was at RAM, I was extremely fortunate to be approached by Matt Shieman, who I had managed a re­furbishment project for on a couple of airplanes. Matt asked me if I ever wanted to start a company, he would like to partner with me. About a year later, I decided to leave RAM. I gave Matt a call and true to his word, we immediately formed a partnership and started Aurora Aviation; and engaged in buying, refurbishing, and sell­ing airplanes. A year later, another customer, Dale Grif­fin, offered to buy into our fledgling company, and now we were three. We eventually had avionics, maintenance, and an FBO and flight school. A couple of other investors came and went, but Matt and Dale have hung in for over 26 years, providing financial support, business guidance, mentoring, and advice. I would also lean on them heavily in the coming years as our lives were about to change.

Fate Intervenes

One day, a dealer acquaintance of mine called me about a deal he thought I might be interested in – he was taking an STC in on trade on an airplane that he was selling, and he knew that I had worked at RAM and might have an idea of what the STC was worth. It was an STC to upgrade the engines on a Conquest I from the PT6A-112 engines to the newer and much more powerful PT6A-135 engines. My heart jumped into my throat. This was exactly what I had been looking for, and it just fell into my lap. But a Conquest? I loved the airplane, but I knew there were not many out there. Would it work?


I ran the deal by Matt and Dale, but none of us really knew what the STC was worth. There was not anyone upgrading the engines on Conquests or anything else to any great success at the time, and the fact that there were only 236 Conquests ever built, there was not much of a potential market. Who would be willing to pay over dou­ble the cost of an overhaul for a brand-new engine just to go 25 knots faster? It made no financial sense to buy this STC. But the price of the STC was right, and to three airplane nut pilots, the thought of creating the fastest Conquest I on the planet was just too enticing. So, with a lot of hope and determination, we all agreed to move for­ward with the purchase of the STC, and on May 1, 1999, Blackhawk Modifications, Inc. was born.

Build It and They Will Come

What is smart about Pratt is that their engines of a cer­tain series are all nearly the exact same dimensions, with only internal changes made to give it more horsepower. This made the installation “plug and play,” with no cowl, firewall, or engine mount changes needed that can add hundreds of thousands of dollars to an STC certification, not to mention increased part counts. Dale volunteered to buy a Conquest to use as the flight test plane to add some other STCs and then use as a demonstrator. We used the plane to add the McCauley BlackMac Props to the STC, as well as changed the engine from the no longer pro­duced PT6A-135 version to the new style PT6A-135A ver­sion, which has a much better compressor and air-cooled guide vanes, giving the engine more thermodynamic horsepower at altitude. Also, the -135As did not require the extra boost pumps that the -135 engines did. The en­gine fit the 425 like a glove.

First Flight

Finally, the day came to do the first flight. I settled into the left seat while Mike Moore, our Director of Main­tenance, sat in the right seat to monitor the gauges and note any splits in gauge readings or power levers. After some extensive ground runs, we were ready for takeoff. As I lined up on runway 17 at McGregor Executive, the moment I had been dreaming of since 1984 was about
to happen. I held the brakes and slowly advanced the throttles to 1244 lbs. of torque. The ITTs didn’t get much above 680 since the mechanical horsepower limit was 750, and we were only using 450 of those horses for take­off due to the airframe limitation of the Conquest.

The airplane jumped off the runway before I even rotat­ed. Our test plan was to climb to various altitudes and write down data – climb rates, IAS, fuel flows, engine gauge readings, etc. Going through 13,000 feet, I noticed a low rumbling sound that I had never heard with the stock -112 engines. I glanced at Mike with a raised eye­brow. “That’s those big compressors doing their job,” he replied. I just smiled. As we rocketed through 20,000′ at 2000 fpm, I kept thinking, This thing is a beast!

We flew around at 25,000′ for an hour or so and clocked 293 knots TAS at max ITT of 805 but within torque and Ng limitations – caveat, we were about 800 lbs. under max gross weight. I then set the power to a more leisurely setting of 775 degrees ITT – 30 degrees below the 805 de­gree max ITT limit – and after 10 minutes or so, we noted 285 KTAS: 25 knots faster than the airplane did with the -112 engines. We descended to around 10,000′ and did an inflight engine shut down. She handled beautifully. I then climbed back up to see how high we could get on one engine on an ISA plus-10 day. The stock -112 charts said that 15,000′ was where we would end up based on our current weight. We climbed to FL200 before the rate of climb finally tapered off to less than 100 fpm. We could top any mountain in America on one engine.

That first flight procedure became part of my demo flights to prospective customers in the years to come. Fly to FL250, show the speed, descend to 10,000, shut down one engine, climb back up to 20,000 and watch the customer’s mouth hang open. Dale allowed me to use his Conquest to show the market what it could do. I think I flew it more that first year than he did, but I don’t think I ever failed to close the sale when I gave those demo rides. Once they understood the safety margin it added, the speed, and amazingly quiet cabin as well, they were smitten.

The Conquest I is a pilot’s airplane. It’s basically a 1985 Cessna 421C with turbine engines on it; the low main­tenance of a piston twin airframe with the high perfor­mance and reliability of a turbine. I love the King Airs, but as a personal airplane, the Conquest I is just an amazing machine.

As Blackhawk’s story continued, we added many models to our stable of products. Matt would buy the next test airplane – a C90, which is one of our most successful products to date. Even as small as the overall market on the airplane is, we still do one or two Conquests a year. People just love the airplane and all that it can do, and the airplane holds its resale value well.

To date, we have upgraded 62 Conquests to the 135A with two more on the schedule. Not one owner has ever said, “I wish I had never done the upgrade so I could go slower,” and that is about the best endorsement you can get.