Pilatus PC-12: The Value of Only One Engine

Pilatus PC-12 NG does things other airplanes can't and costs less.

__Many pilots want to fly a 1,000-mile trip nonstop. That’s about the distance from New York to southern Florida, or from Chicago to Miami, or from Atlanta to Aspen. And people want to take along all of their family, friends and stuff on these trips.

A bunch of airplanes can fly the 1,000-mile trip downwind, or on that mythical flight-planning day when there is no wind, but very few can make it nonstop every time upwind, particularly in the winter months when the wind aloft at turbine airplane altitudes often exceeds 100 knots. And even fewer airplanes can make the trip upwind with a big payload.

The exception is the Pilatus PC-12 NG single-engine turboprop, which can lug at least 1,200 pounds of payload over 1,000 miles against the strongest headwind and do it every time. And the PC-12 NG can fly the trip at maximum cruise speed of around 260 knots, not the much slower long-range speed. The reason it can reliably make the flight so many pilots want is because the PC-12 has more than 1,500 miles of still air range with a 1,200-pound payload. That means the PC-12 has the range to nearly span the continent downwind, and can always make it across the country upwind with only one stop.

Having great range is a terrific asset for any airplane, but there is an adage in aviation that an airplane can “outfly its cabin,” meaning the endurance of the passengers expires before the fuel supply does. While most pilots are willing to sit in a cramped cockpit for hours on end to avoid a fuel stop, nonpilot passengers are not. They demand room to move around, a private and usable lavatory and access to drinks and food.

Again, the PC-12 stands out for having a cabin almost 17 feet long and 5 feet wide, with 4 feet 10 inches of headroom. There is a private lav, and luggage is accessible in the rear of the cabin while in flight. The cabin equals, or at least rivals, some midsize business jets that have similar range.

All of the size, range and payload capabilities of the PC-12 flow from the fundamental design choice of using only one engine. Carrying the fuel to feed a second engine, plus the weight and drag of the engine itself, all cut into range and payload. The second engine and its costs also mean the twin-engine turboprop that comes closest to the PC-12 in cabin size and full fuel range falls hundreds of miles short when the same payload is aboard, and costs at least a million dollars more to buy.

It seems the Swiss engineers at Pilatus were thinking more of utility and operating flexibility than personal and business travel when they created the PC-12 in the early 1990s. That’s why the airplane has a huge cargo door in the aft fuselage, landing gear designed for the roughest runway, and a big fuselage to haul stuff. Early sales went to utility operators such as physicians in Australia who bought the airplane to fly into the bush to treat people in the remotest of areas. But when pilots in the United States learned what the PC-12 could do, they wanted to use it to fly their own missions that other airplanes just can’t accomplish.

Pilots flying utility missions into the wild have long made peace with the idea of having only one engine. Engine failure is, of course, a risk, but the list of risks in bush flying is so long that having only one engine is certainly not at the top. But would pilots and their passengers pay millions of dollars for an airplane with only one engine? Pilatus couldn’t be certain, so, as Cessna did when it created the Caravan, Pilatus aimed mostly at the utility market, and any business and personal use of the airplane would be a bonus.

A combination of good market timing, high fuel prices, the simplicity of single-engine operation for the owner pilot and, of course, the legendary reliability of the Pratt & Whitney PT6 turboprop engine made the single-engine PC-12 acceptable, and even desirable, to a huge segment of business aviation. Many understood immediately that the PC-12’s remarkable capabilities are a result of having only one engine, and that it would cost so much more to get the same capabilities in a twin-engine airplane.

The Spin Question All single-engine airplanes, including turboprops, must demonstrate the ability to recover from a one-turn spin in no more than one additional turn after recovery controls are applied. For an airplane the size of the PC-12, and considering its very long CG range, that spin recovery requirement could prove difficult to meet.From the outset, Pilatus engineers decided to address the requirement by including a stall barrier system as is found in most larger jets. Dual angle-of-attack sensors mounted on probes near each wingtip on the PC-12 sense when the wing is approaching a stall and command a stick pusher to forcefully move the control wheel forward. Because the pusher prevents an aerodynamic stall, there can be no spin and thus no need to demonstrate spin recovery.To the Federal Aviation Administration, the stick pusher delivers safety equivalent to that in the spin recovery demonstration. In another finding of equivalent safety, the FAA has certified the NG to stall at 67 knots at its maximum takeoff weight. The FAA determined that the crashworthiness of the PC-12 seats, restraints and airframe provides the same degree of safety as there would be without those elements – and thus approved the stall speed increase from the general requirement of 61 knots maximum for singles.* * * Real Dual Electrics Many single-engine airplanes now have dual generators or alternators, but the NG has a complete split-bus dual electrical system just like recently designed jets have. There are also two batteries, one for each bus, and an additional emergency battery to power backup equipment should all else somehow fail.As in the jets, both generators have the same capacity, 300 amps. The generator on the No. 2 bus also serves as the starter. After engine start, the two electrical buses are independent of each other, so a single short or other failure can’t damage the other bus.Unlike in most singles with dual generators, both units on the NG are gear-driven by the engine instead of belt-driven. Belt failure is just one more thing an NG pilot doesn’t need to worry about.

The faith in the PT6 engine is so great that some flight departments that operate medium- and long-range business jets have added a PC-12 to their fleets for missions that don’t make sense in the jets. There is a booming passenger charter business flown in PC-12s, and passengers don’t give the single engine a second thought. And in real-world operation the PC-12 safety record has been better than that of turboprop twins. The comparison is complicated by the fact that there are so many more twins flying, and the PC-12 fleet on average is much newer, but it is still conclusive that the PC-12 has not yielded anything to the twins in terms of overall safety.

During the 15 years or so that the PC-12 has been in service, Pilatus has made many improvements to the original design. Maximum takeoff weight has gone up, a more powerful engine is now used, and the entire avionics system was transformed about two years ago with certification of the Honeywell Apex system. Pilatus renamed the airplane PC-12 NG when Apex was introduced, with the NG standing for Next Generation.

Apex uses four big 10.4-inch flat-glass displays with the two MFDs stacked in the center as they are in some newly designed large-cabin jets. In fact, much of the display symbology and system operation is derived from Honeywell’s Epic avionics system, which is used in many larger business jets. Apex has a full CAS (crew advisory system), meaning all crew alerts are presented in plain language on the displays. The messages are prioritized in order of urgency and emphasized by using different colors. Transitioning from the “idiot lights” of an annunciator panel to a full CAS is a really big deal in terms of complexity and cost, but a CAS is so much more informative and useful for the pilots.

The PC-12 has always had a very stout and hardworking look about it, both inside and out. In the cockpit, the knobs, switches and flight controls all looked like they belonged in a bigger airplane, even though the PC-12 is plenty big. But Pilatus hired BMW Designworks to create the cockpit in the NG version, and the impression is more sleek and modern. I felt as though I were in the newest business jet instead of a single-engine airplane when I got to fly the NG.

The PT6A-67P in the NG is one of the most powerful in the PT6 turboprop family, with the capability to produce 1,845 shp. Pilatus restricts maximum output to 1,200 shp, so the difference between that and the maximum power potential is available on very hot days, or at higher altitudes. This “flat rating” is common in turbine engines, but the NG has one of the largest percentage differences between maximum engine power potential and the amount of power actually transmitted to the prop. The huge amount of flat rating means the NG can operate from very high-elevation runways on hot days, and can cruise faster at its 30,000-foot ceiling.

The quality of the metalwork in the PC-12 has always been first-rate, but executive interiors had not matched other business airplanes of its size in terms of sophistication and materials. With the NG, however, the cabin appointments are better and the airplane is getting closer to its competition in that category. Pilatus offers a variety of interiors for executive, high-density, cargo or a combination of cargo and passenger missions. Even with a typical six-seat executive interior, there is still gobs of space in the aft cabin for baggage. You can even load your Harley through the big cargo door, as Pilatus has demonstrated at many airshows.

The wing is long and slender with a span of more than 53 feet and an aspect ratio of 10.2. The flaps extend along about 80 percent of the trailing edge, leaving room for rather short-span ailerons. The flaps need to be very large because certification rules limit the maximum stalling speed of single-engine airplanes — including single-engine turboprops — to 61 knots. An effective flap is a good way to lower stalling speed while keeping total wing area small enough to be efficient at cruise.

Short-span ailerons are typically less effective and require more stick force than longer-span surfaces do, and that is true in the PC-12. However, Pilatus added servo tabs to each aileron several years ago, which greatly reduced roll force. The PC-12 is still not light on the controls, but the harmony of forces is pretty good, and it’s easy to fly the airplane smoothly.

The Apex avionics system makes use of what Honeywell calls INAV, for integrated navigation. What that means is that you can perform most flight-plan and other avionics entries using a cursor and menus. Pilatus recently installed a track ball on the center pedestal so you can use your fingers to position the cursor on the four displays. Graphical flight planning is as easy as putting the cursor on the moving map over the fix you want to add to the flight plan and clicking. Drop-down menus are a click away to select frequencies, view checklists, look at system synoptic pages and so on.

As in some jets, you can see everything you need to fly the NG on the PFD (primary flight display) in front of you, including engine, navigation and communication frequencies. Of course, you can move data around by opening and closing windows and can pretty much configure everything except the actual primary instrument display to your liking. With a host of line-select keys on the edges of each display, it doesn’t take long to figure out how to operate the system. Synthetic vision and enhanced GPS navigation based on WAAS are expected to be available later this year.

Pilatus chief pilot Peter Duncan and I had the Apex system programmed for takeoff and quickly worked through the mercifully short checklists in just a few short minutes after engine start. As you can imagine, setting enough rudder trim for takeoff is a big deal with that much power going to a single propeller, so you dial the trim way over to counteract the torque. I realized a couple of minutes after takeoff that I wasn’t pushing on the rudder pedals even though I had forgotten to adjust the trim from the takeoff position. What I had done is turn on the yaw damper, which is now a smart system, and it adjusted the trim automatically. One more issue with a single-engine airplane resolved.

The autopilot in the Apex system is excellent and shows off its jet heritage by flying the NG with smoothness and precision. I watched the Apex system fly several approaches, including automatically entering holds and procedure turns and exhibiting all of the stuff that is expected for new avionics systems but is still amazing. One of the most unusual features of Apex is that it has coupled go-around, meaning when you push the go-around button on the throttle, the autopilot remains coupled. In other airplanes, without an autothrottle the autopilot typically uncouples at go-around and you need to re-engage the system. I like the autopilot-coupled go-around, but some certification types worry the human pilot will forget to advance the power if the autopilot is flying. That makes no sense to me, and I think Pilatus and Honeywell got it right.

The PC-12 can use rinky-dink runways of less than 2,000 feet, but it can also fit in smoothly at busy airports, because you can extend the landing gear at up to 180 knots and approach flaps at 165 knots. And I don’t think you can ever be flying too fast on final in the airplane because of the massive speedbrake mounted on the nose. When you pull the power back to idle, the propeller blades go to flat pitch and the propeller becomes a huge disk of drag. You can fly amazingly steep approaches with the engine at idle, or can slow from jet approach speeds to a normal landing in almost no distance by chopping the power.
The long-stroke trailing link main gear is designed for unimproved surfaces, so a normal landing on pavement is a thing of beauty. With reverse thrust from the big propeller, you hardly need brakes.

The PC-12 has demonstrated that people will fly single-engine turboprops, and pay more than $4 million for them. For the big majority of pilots, the answer to the question of how many engines you need is “enough to do the job,” and in the case of the PC-12, the magic number is one.


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