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
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
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.