The World’s Safest General Aviation Aircraft: The Pilatus PC-12
by Vaughn Olsen
The purpose of this article is to offer some of the reasons why the Pilatus PC-12 is probably the safest aircraft of its class in the world.
The Pilatus PC-12 is a state-of-the-art single engine turboprop aircraft. Since the first date of manufacture, all single engine turboprop aircraft combined have compiled over 6,000,000 (six million) flight hours with no (that’s zero) fatalities due to engine failure.
The reasons for multiple engines on aircraft are simple. In the early years of aviation aircraft engines lacked both power and reliability, thus multiple engines were required to lift high payloads and dependably deliver them to their destinations. The early Dorniers and Sikorskys, followed by B-36′s and B-52′s and DC-4′s, 6′s, 7′s and Constellations are all cases in point. The trend now in commercial aviation, as engines have become more powerful, reliable and economical, is back to fewer engines. The Boeing 757, 767, 777 and some Airbus Industry aircraft illustrate this. These modern, safe, and efficient aircraft fly global routes, over oceans on two engines, while their immediate predecessor, the 747, used four.
Everyone knows tactical aircraft like the Corsairs and Mustangs of WW-II and later A-4′s and F-16′s can carry a much higher percentage of their gross weights as payload than can their multi-engine bomber counterparts.
The PC-12 is the first single engine turboprop to offer not only payload-range capabilities far exceeding those of its competition, both single and twin, but remarkable efficiency, versatility, simplicity, and more to the point, safety, as well. This is because the PC-12 is a single and is not burdened with the weight, drag, complexity, and vices of twin engines.
What about safety? Remember the “one a day in Tampa Bay” legacy of the Martin B-26 medium bomber of WW-II? The problem was what happened when one of its two powerful R-2800 engines failed after takeoff or in the landing pattern (where failures most often occur). The asymmetrical thrust of the operating engine created horrendous yawing and rolling moments. If these were not instantly and instinctively countered by a current, expertly trained airman, the results were disastrous.
The same problems exist today in all twin engine propeller driven aircraft, thus the higher rate of fatal accidents in twins. Even those few with auto-feather are not immune to the laws of aerodynamics, and the incorporation of this feature only serves to underscore the inherent danger.
To digress further on the perils of twins; remember, if the pilot is current, well trained, and does everything perfectly upon the failure of an engine after takeoff and succeeds in keeping the aircraft right-side up, many twins, especially at high gross weights, lack sufficient power to climb on one engine and are going in anyhow, under the marginal control and high Vmc of reduced power on one engine.
This is where twin engine propeller driven aircraft and jets really are at a disadvantage. They lack the fuselage structure to protect the occupants that all single engine aircraft, and the PC-12 in particular, have.
This structure consists of fuselage longerons, an incredibly strong cockpit carry through structure, comparable to a NASCAR stock car, and a titanium fire wall. All of these are designed to support the weight and torque of a massive power plant and propeller that is further supported by an incredibly strong steel tube engine mount assembly. This sturdy mass around and ahead of the occupants serves to protect them to a very high degree in a forced landing situation, where passengers and crew in a twin or jet have nothing more than fuselage skin around them and some avionics and possibly baggage ahead of them for protection. Think of the PC-12 as a Volvo and the jet/twin alternatives as old Volkswagen Beetles!
The PC-12, like it’s predecessors the PC-9, PC-7 MKII, PC-7, PC-6, P-3 and P-2, is an incredibly well designed, built, and tested aircraft. The first PC-12 accident showcases the integrity of the airframe. The aircraft was literally flown through a brick wall (cinder block). After take-off, the nose gear snagged a barbed wire fence that was atop a cinder block wall, that the main gear impacted. The mains rotated aft approximately 90 degrees compromising the rear spar and flaps and puncturing a fuel tank. In this configuration the aircraft was flown approximately 30 nautical miles to a major airport, landed on the nose wheel and aft fuselage, and ended up 500 feet off the runway and 90 degrees off runway heading in the rough. There were no injuries, no nose gear failure, no prop strike, no engine damage, and no fire. The aircraft saved the occupants to fly another day, and the owner promptly ordered a new PC-12. After an extensive factory supervised re-construction utilizing factory new wings, gear, fuselage skin and components, this aircraft has re-joined the fleet.
The Pilatus PC-12 is the only single engine aircraft in the United States to be exempted from the FAR Part 23 61 knot stall speed requirement. This has been increased to 65 knots due to the PC-12′s superior construction. In other words, the FAA is willing to certify the PC-12âs safety to a higher standard than any other!
The PC-12 is a single engine aircraft powered by a Pratt & Whitney, PT-6, the most dependable aircraft engine ever produced, anywhere. The -67B variant used on the PC-12 produces 1605 shaft horsepower and is flat-rated to 1200 horsepower. In a 6000 pound empty weight aircraft, this is a better horsepower-to-weight ratio than a WW-II Mustang fighter with 1490 combat only horsepower in a 7500 pound airframe. This concept of putting a massively powerful engine on a light and efficient airframe, then rating it at only 75% of its power means that the stresses of the higher temperatures (ITT) at which it was designed to run are never imposed upon it. Further, in the conservative Swiss manner, this 1200 horsepower is never used, except momentarily at takeoff. High speed cruise, at book torque, yields an average ITT of only 700 which is 60 less than maximum continuous (at the max continuous power of 760 ITT and 1000 horse-power this engine has a TBO of 3500 hours). This further reduction in ãutilized powerä creates huge margins of safety, reliability, economy, and performance in icing and high density altitude situations. Other manufacturers that use the PT-6 in both twin and single applications run them at higher temperatures (power) to attain their claimed performance specs.
Pilatus builds more single engine turboprop aircraft than all other manufacturers in the world, combined! The Pilatus PC-9 is the aircraft that recently won the multi-billion dollar JPATS Contract from the United States government in competition with the worlds foremost suppliers of military aircraft. The PC-9, already proven in widespread use by Air Forces around the world, is being built under license by Raytheon, as the PC-9 MKII, and will be the primary trainer for both the Air Force and Navy Training Commands well into the next century.
The PC-12 is a “clean sheet of paper” ’90′s design that is not burdened with pre-existing design criteria or components, such as wings, from previous aircraft. The single engine, light weight, incredibly clean aerodynamics and state-of-the-art structure allow it to operate at about half the direct operating cost of a Beechcraft B200 King Air. More importantly, it creates a huge additional margin of safety.
This aircraft is, literally, a glider. At maximum gross weight, it glides an incredible 2.6 nautical miles per 1000 feet of altitude, and does it at a very slow 114 KTS. At 20,000 feet above the terrain, (which is a normal minimum cruise altitude in the United States), the PC-12 is in the center of a no-wind 104 nautical mile diameter circle into which it can glide. In addition to this incredible glide range, which always yields multiple suitable airports, the time aloft is 25 minutes and the PC-12 lands very slowly when finally asked to do so. In addition to its high speed, high altitude, above-the-weather pressurized cruising comfort, the PC-12 is virtually a STOL aircraft.
The book stall speed for a high gross weight, executive configured PC-12 at maximum gross is only 65 KTS. (Remember the FAR Part 23 61/65 knot stall speed/exemption?). We all know the definition of a stall as used by the rest of the aircraft builders in the world. Pilatus, true to the conservative philosophy that shaped the PC-12, chose to define the stall differently. The pilot operating handbook charts are predicated upon the stall being defined as stick pusher activation. A sophisticated stall warning system utilizing angle of attack and an air data computer incorporates a stick shaker and pusher. The shaker activates at an angle of attack value approximately 10 KTS above the actual stall, and the pusher, at approximately 5 KTS above the actual stall. In other words, at a maximum take-off weight of 9921 pounds, the PC-12 stalls at about 59 KTS, and at average gross weights approximately 50 KTS.
All of this simply means that in the event of an engine-out landing the touchdown speed in a PC-12 is far slower than any aircraft in the world with which it can be reasonably compared. This, in combination with its incredible demonstrated crashworthiness, as attested by the FAA, the incredible safety record of the PT-6 engine, and no twin engine vices or weaknesses, yields the safest general aviation aircraft in the world.
Vaughn B. Olsen is a Pilatus Demonstration Pilot for Western Aircraft Inc. based in Boise Idaho.
Naval Aviator, Former U.S.M.C. F-4 Fighter Pilot and Naval Air, Advanced Training Command Instructor Pilot/Fighter, Standardization Officer, Confederate Air Force Fighter Check Pilot and Formation Examiner, Confederate Air Force Flight Safety Board Member, Confederate Air Force Flight Evaluation Board Examiner, F-4U Corsair Airshow Pilot
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