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Pratt & Whitney Canada PT6

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A PT6A-20 on display at the Canada Aviation and Space Museum
Type Turboprop / turboshaft
National origin Canada
Manufacturer Pratt & Whitney Canada
First run 1960[1]
Major applications AgustaWestland AW139
Beech King Air and Super King Air
Cessna 208 Caravan
de Havilland Canada DHC-6 Twin Otter
Pilatus PC-12
Number built 51,000 (as of November 2015)[2][needs update]
Variants Pratt & Whitney Canada PT6T

The Pratt & Whitney Canada PT6 is a turboprop aircraft engine produced by Pratt & Whitney Canada. Its design was started in 1958, it first ran in February 1960, first flew on 30 May 1961, entered service in 1964, and has been continuously updated since. The PT6 consists of two basic sections: a gas generator with accessory gearbox, and a free-power turbine with reduction gearbox. In aircraft, the engine is often mounted "backwards," with the intake at the rear and the exhaust at the front, so that the turbine is directly connected to the propeller. Many variants of the PT6 have been produced, not only as turboprops but also as turboshaft engines for helicopters, land vehicles, hovercraft, and boats; as auxiliary power units; and for industrial uses. By November 2015, 51,000 had been produced, which had logged 400 million flight hours from 1963 to 2016. It is known for its reliability, with an in-flight shutdown rate of 1 per 651,126 hours in 2016. The PT6A turboprop engine covers the power range between 580 and 1,940 shp (430 and 1,450 kW), while the PT6B/C are turboshaft variants for helicopters.


In 1956, Pratt & Whitney Canada's (PWC) president, Ronald Riley, ordered engineering manager Dick Guthrie to hire a team of gas turbine specialists to design a small gas turbine engine. Demand for the Wasp radial engine was still strong and its production was profitable but the aim was to become Canada's prime engine company by focusing on a small gas turbine engine. Riley gave Guthrie a modest budget of C$100,000. Guthrie recruited twelve engineers with experience gained at various places including the National Research Council in Ottawa, Orenda Engines in Ontario, Bristol Aero Engines and Blackburn Aircraft.[3] They completed the detailed design of an engine for Canadair's small jet trainer, the CL-41. It was a 3,000-pound-force (13 kN) thrust turbojet but the design was taken over by P&WA who developed it into the Pratt & Whitney JT12. The team had to wait for market assessments to define their next engine, a 450 shaft horsepower (340 kW) turboprop for twin-engined aircraft, the PT6.[4] The early development of the PT6, which first ran in December 1963,[1][5] was beset with engineering problems, cost overruns and lack of sales. It was almost cancelled.[4] The team lacked the ability to deal with the technical difficulties, i.e. how to develop the engine, because, as one of the team Elvie Smith recalled, they came from research and design backgrounds. They learned how to run a development program, such as testing around the clock rather than on one shift, from a PWA team which directed the development for several months.[6]

The PT6 first flew on 30 May 1961, mounted as a third engine in the nose of a Beech 18 aircraft which had been converted by de Havilland at its Downsview facility in North York, Ontario. Full-scale production started in 1963, with service entry the following year. The Beech 18 continued as a PT6 and propeller flying test-bed until it was replaced with a Beech King Air in 1980. The King Air test-engine or propeller replaced one of the standard ones. In 1974 the Beech 18 had been unable to fly fast enough and high enough to test the PT6A-50 for the de Havilland Canada Dash 7 so a Vickers Viscount was modified as a PT6 test-bed with a Dash-7 installation in the nose.[7]

The first production PT6 model, the PT6A-6, was certificated in December 1963. The first application was the Beech Queen Air, enticing the U.S. Army to buy a fleet of the U-21 Ute variant. This helped launch the King Air with Beechcraft selling about 7,000 by 2012.[8] From 1963 to 2016 power-to-weight ratio was improved by 50%, brake specific fuel consumption by 20% and overall pressure ratio reached 14:1.[9] Its development continues and while today its basic configuration is the same as in 1964, updates have included a cooled first-stage turbine vane, additional compressor and turbine stages and single-crystal turbine blades in the early 1990s. Its pressure ratio is 13:1 in the AgustaWestland AW609 tiltrotor, the highest that can be used without cooled turbine blades.[10]

In response to the General Electric GE93, in 2017 Pratt & Whitney Canada started testing core technology and systems for a proposed 2,000 shp (1,500 kW) engine to replace the most powerful versions of the PT6.[11] It was considered likely to be a development of the PT6C core, and would fit between the 1,750 shp (1,300 kW) PT6C-67C/E and the 2,300 shp (1,700 kW) PW100 family. It was expected to be ready to launch by the end of 2017 for an initial helicopter platform with a 10-15% reduction in brake specific fuel consumption.[12] This 2,000 hp engine would target a possible new market such as a Super PC-12, a more powerful TBM, or a bigger King Air.[13]


When de Havilland Canada asked for a much larger engine for the DHC-8, roughly twice the power of the Large PT6, Pratt & Whitney Canada responded with a new design initially known as the PT7, later renamed Pratt & Whitney Canada PW100.


Epicyclic reduction gears on Pratt & Whitney Canada PT6 gas turbine engine.

The rate at which parts deteriorate in a gas turbine is unbalanced insofar as the hottest parts need replacing or repairing more often than the cooler-running parts. If the hotter parts can be removed without disturbing the rest of the engine, for example without removing the complete engine from the aircraft, maintenance costs are reduced. It was achieved with the PT6 by having the hottest parts, the gas generator turbine and combustor, at the propeller end. They are removed without disturbing the rest of the engine with its connections to the aircraft. This arrangement was patented by designer Newland, one of the original PT6 team.[14] A similar general arrangement with a free-turbine power take-off at the exhaust end (the 1,000 shp (750 kW) P.181 engine) had been shown by Armstrong Siddeley Motors at the Farnborough Airshow in 1957.[15]

An early design improvement, incorporated in the PT6A-20,[16] was the pipe diffuser patented by Vrana, another of the original PT6 team.[17] It replaced the vaned type diffuser used in centrifugal compressors. The pipe diffuser became standard design practice for P&WC.[18] Another design change improved the part-speed functioning of the compressor. It is common to bleed air from a compressor to make it work properly at low engine speeds. The PT6 has a bleed arrangement which reuses the bleed air by returning it in a tangential direction at the entry to the compressor, an idea patented by Schaum et al. and titled "Turbine Engine With Induced Pre-Swirl at Compressor Inlet".[19] It acts like a variable vane and is known as a "Jet-Flap".

All versions of the engine consist of two sections that can be easily separated for maintenance: a gas generator supplies hot pressurized gas to a free power turbine.[20] The starter has to accelerate only the gas generator, making the engine easy to start, particularly in cold weather.[20] Air enters the gas-generator through an inlet screen into the low-pressure axial compressor. This has three stages on small and medium versions of the engine and four stages on large versions. The air then flows into a single-stage centrifugal compressor, through a folded annular combustion chamber, and finally through a single-stage turbine that powers the compressors at about 45,000 rpm. Hot gas from the gas generator flows into the power turbine, which turns at about 30,000 rpm. It has one stage on the small engines and two stages on the medium and large ones. For turboprop use, this powers a two-stage planetary output reduction gearbox, which turns the propeller at a speed of 1,900 to 2,200 rpm. The exhaust gas then escapes through two side-mounted ducts in the power turbine housing. The turbines are concentric with the combustion chamber, reducing overall length.

In most aircraft installations the PT6 is mounted so that the intake end of the engine is towards the rear of the aircraft, leading to it being known by many as the "back-to-front" engine.[4] This places the power section at the front of the nacelle, where it can drive the propeller directly without the need for a long shaft. Intake air is usually fed to the engine via an underside mounted duct, and the two exhaust outlets are directed rearward. This arrangement aids maintenance by allowing the entire power section to be removed along with the propeller, exposing the gas-generator section. To facilitate rough-field operations, foreign objects are diverted from the compressor intake by inertial separators in the inlet.[21] In some installation such as the PT6A-66B version in the Piaggio P.180 Avanti, the engine is reversed, with the propeller acting as a "pusher", the accessory gearbox facing the front of the aircraft.

From left to right: propeller mount, reduction gear, exhaust, 2-stage free power turbine, 1-stage gas generator turbine surrounded by the combustor, 1 centrifugal then 4 axial compressor stages, intake, and accessories

Operational history[edit]

By the 40th anniversary of its maiden flight in 2001, over 36,000 PT6As had been delivered, not including the other versions.[22] Up to October 2003, 31,606 delivered engines have flown more than 252 million hours.[23] Till November 2015, 51,000 have been produced.[2] The family logged 400 million flight hours from 1963 to 2016.[9]

The PT6 family is known for its reliability with an in-flight shutdown rate of 1 per 333,333 hours up to October 2003,[23] 1 per 127,560 hours in 2005 in Canada,[24] 1 per 333,000 hours from 1963 to 2016,[9] 1 per 651,126 hours over 12 months in 2016.[25] Time between overhauls is between 3,600 and 9,000 hours and hot-section inspections between 1,800 and 2,000 hours.[26]

Early PT6 versions lacked a FADEC, autothrottle could be installed as an aftermarket upgrade with an actuator, initially for single-engine aircraft like the PC-12 and potentially in twin-turboprop aircraft.[27] In October 2019 the PT6 E-Series was launched on the PC-12 NGX, the first general aviation turboprop with an electronic propeller and engine control system with a single lever and better monitoring for longer maintenance intervals, increased from 300 to 600 hours, and a TBO increased by 43% to 5,000 hours, reducing engine operating costs by at least 15%.[28] In April 2022, Daher announced that the updated SOCATA TBM-960 would be powered by the PT6E-66XT.[29]


A PT6A-67D engine on a Beechcraft 1900D. The turbine exhaust (copper-colored pipe) is prominent.

The main variant, the PT6A, is available in a wide variety of models, covering the power range between 580 and 920 shaft horsepower (430 and 690 kilowatts) in the original series, and up to 1,940 shaft horsepower (1,450 kilowatts) in the 'large' lines. The PT6B and PT6C are turboshaft variants for helicopters. In US military use, they are designated as T74 or T101.

Several other versions of the PT6 have appeared over time:

  • the Large PT6 added another power turbine stage and a deeper output reduction, producing almost twice the power output, between 1,090 and 1,920 shaft horsepower (810 and 1,430 kilowatts).
  • the PT6B is a helicopter turboshaft model, featuring an offset reduction gearbox with a freewheeling clutch and power turbine governor, producing 1,000 horsepower (750 kilowatts) at 4,500 rpm.
  • the PT6C is a helicopter model, with a single side-mounted exhaust, producing 2,000 horsepower (1,500 kilowatts) at 30,000 rpm, which is stepped down in a user-supplied gearbox.
  • the PT6E is a large PT6A derivative equipped with digital engine control.
  • the PT6T Twin-Pac consists of two PT6 engines driving a common-output reduction gearbox, producing almost 2,000 horsepower (1,500 kilowatts) at 6,000 rpm.
  • the ST6 is a version intended for stationary applications, originally developed for the UAC TurboTrain, and now widely used as auxiliary power units on large aircraft, as well as many other roles.[30]

The PT6A family is a series of free-turbine turboprop engines providing 500 to 1,940 shaft horsepower (370 to 1,450 kilowatts)


variant equivalent

PT6A-6, 6A, 6B 525 500 Heron-TP-XP UAV from Israel[33]
PT6A-11 528 500
PT6A-11AG 580 550 Air Tractor AT-400 (402A / 402B)
Schweizer Ag-Cat G-164B Turbine
PT6A-15AG 715 680 Air Tractor AT-400 (402A/402B)
Air Tractor AT-502, -502A and -502B
Frakes Turbocat Model A / B / C
Schweizer Ag-Cat G-164B Turbine
PT6A-20 579 550 De Havilland Canada DHC-6 Twin Otter Srs. 100-200
PT6A-20A, -20B, -6/C20 579 550
PT6A-21 580 550 Beechcraft King Air C90A / B / SE
Beechcraft Bonanza (turbine conversion)
Royal Turbine Duke
Evektor EV-55 Outback
PT6A-25, -25A 580 550 Beechcraft T-34C Turbo Mentor
Pilatus PC-7 Turbo Trainer
PT6A-25C 783 750 Embraer EMB 312 Tucano
Pilatus PC-7 Mk.II M
PZL-130 Orlik / TC-II Turbo-Orlik
PT6A-27 715 680 Beechcraft Model 99A, B99
De Havilland Canada DHC-6 Twin Otter 300
Harbin Y-12 (CATIC / HAIG)
Embraer EMB 110 Bandeirante
Let L-410 Turbolet
Pilatus PC-6/B Turbo-Porter
PT6A-28 715 680 Embraer EMB 121 Xingu
Beechcraft King Air 100 Series
PT6A-29 778 750
PT6A-34 783 750 Embraer EMB 110 Bandeirante/111
Embraer EMB 821 Carajá
Grumman Mallard (Frakes turbine conversion)
PAC P-750 XSTOL (750XL)
Quest Kodiak (Daher)
Vazar Dash 3 Turbine Otter
De Havilland Canada DHC-6 Twin Otter 400
Thrush S2R-T34
Pilatus PC-6/B Turbo-Porter (STC)
PT6A-34B 783 750
PT6A-34AG 783 750 Air Tractor AT-502B
Frakes/Grumman Turbo-Cat Model A / B / C
Pacific Aerospace 750
PZL-Okecie PZL-106 Turbo Kruk
Schweizer Ag-Cat G-164B/D Turbine
Thrush Model 510P
Thrush S2R-T34
PT6A-35 787 750 Blue 35
PT6A-36 783 750 Thrush S2R-T34 (dry configuration only)
PT6A-38 801 750
PT6A-110 502 475 Schweizer AG-Cat Turbine
Royal Turbine Duke
PT6A-112 528 500 Cessna Conquest I
PT6A-114 632 600 Cessna 208 Caravan
PT6A-114A 725 675 Cessna 208 Caravan 675, 208B
PT6A-116 736 700
PT6A-121 647 615
PT6A-135 787 750
PT6A-135A 787 750 Beechcraft King Air F90-1 / C90GT / C90GTi / C90GTx
Blackhawk XP135A Cheyenne Series
Blackhawk XP135A Conquest I
Blackhawk XP135A King Air 90 Series
Cessna Conquest I
Lancair Evolution
Silverhawk 135 / StandardAero C90 / E90
StandardAero Cheyenne Series
StandardAero King Air F90
T-G Aviation Super Cheyenne
Vazar Dash 3 Turbine Otter
PT6A-140 912 867 Cessna Grand Caravan EX
PT6A-140A 945 900 ASIC ULtimate Grand Caravan (upgrade)
Blackhawk Aerospace XP140 (Caravan upgrade)
Evolution Aircraft EVOT-850 (formerly Lancair)
PT6A-140AG 911 867 Air Tractor 502XP
Thrush Model 510P


variant equivalent

PT6A-40 749 700
PT6A-41, -41AG 903 850 Beechcraft King Air 200 / B200
Piper Cheyenne III / IIIA
Beechcraft C-12 Huron
Thrush S2R-T34 (-41 and -41AG)
PT6A-42, -42A 903 850 Beechcraft C-12 Huron E and F
Beechcraft King Air 200 / B200
Blackhawk XP42 King Air 200
StandardAero King Air 200
Blackhawk XP42A C-208 Caravan Series (-42A)
Piper Meridian (-42A)
Thrush S2R-T34
Indonesian Aerospace N-219
PT6A-45 1070 1020
PT6A-45R, -45A, -45B
PT6A-50 1022 973 de Havilland Canada DHC-7 Dash 7
PT6A-52 898 850 Beechcraft King Air B200GT / 250
Blackhawk XP52 King Air 200 / B200
Enhanced Aero B200GTO
StandardAero King Air 200 / B200

Piper PA-46 (M700 Fury)

PT6A-60, -60A 1113 1050 Beechcraft Super King Air 300 / 350
PT6A-60AG 1081 1020 Air Tractor AT-602
Ayres Thrush 550P
Ayres Thrush 660
PT6A-61 902 850 Short C-23 Sherpa
PT6A-62 1008 950[34] KAI KT-1 / KO-1
Pilatus PC-9 Turbo Trainer


variant equivalent

PT6A-64 747 700 EADS Socata TBM 700
PT6A-65B, -65R[31] 1249 1173 Beechcraft 1900 / 1900C
Polish Aviation Factory M28 Skytruck
PT6A-65AG, -65AR[31] 1298 1220 Air Tractor AT-602
Air Tractor AT-802 / 802A / 802AF / 802F
Ayres Thrush 660 / 710P
AMI DC-3 (-65R)
Dodson International Turbo Dakota DC-3
Shorts 360 Advanced (-65AR)
PT6A-65SC 1100 Cessna 408 SkyCourier
PT6A-66, -66A, -66D 905 850 National Aerospace Laboratories SARAS
Piaggio P.180 Avanti
Ibis Ae270 HP (-66A)
Daher TBM 850, 900, 910, 930 and 940 (formerly EADS Socata TBM) (-66D)
PT6A-66B, -66T 1010 950 Piaggio P180 Avanti II (-66B)
PT6A-67, -67A, -67B 1273 1200 Beechcraft RC-12 Guardrail (-67)
Beechcraft Starship (-67A)
Epic LT (-67A)
IAI Heron TP (-67A)
PT6A-67B, -67P
1272 1200 Pilatus PC-12 (-67B)
Pilatus PC-12NG (-67P)
Pilatus PC-12NGX (PT6E-67XP)
PT6A-67D 1285 1214 Beechcraft 1900D
PT6A-67AF, -67AG, -67R, -67T, -67RM 1294 1220 Air Tractor AT-802 / 802A / 802AF / 802F (-67AG)
Ayres Thrush 710P (-67AG)
Basler Turbo BT-67 (-67R)
Shorts 360 / 360–300 (-67R)
PT6A-67E 1276 1200
PT6A-67F 1796 1700 Air Tractor AT-802 / 802A / 802AF / 802F
PT6A-68 1324 1250 T-6A Texan II
PT6A-68B, -68C, -68T, -68D 1691 1600 Pilatus PC-21 (-68B)
Embraer EMB-314 Super Tucano (-68C)
TAI Hürkuş (-68T)
(PT6A-20) United States military designation for the PT6A-20/27, used in the Beechcraft U-21 Ute.
United States military designation for the T101-CP-100 / PT6A-45R, used in the Shorts 330 and Shorts C-23 Sherpa.
The PT6B-9 is a 550 horsepower (410.1 kilowatts) turboshaft engine for use in helicopters; a later mark of PT6B is rated at 981 horsepower (731.5 kilowatts).
The PT6C is a 1,600 to 2,300 shaft horsepower (1,200 to 1,700 kilowatts) engine for helicopters and tiltrotors.
The PT6D-114A is based on the PT6A-114A; the main difference is the deletion of the second-stage reduction gearing and output shaft, because the engine is intended for integration with a combining gearbox incorporating power turbine governors and a propeller output shaft.[36]
Soloy Dual Pac
2x PT6D-114A engines driving a single propeller through a combining gearbox, capable of independent operation.
Twin PT6 power units combining outputs through a gearbox for use in helicopters.
The ST6 is a variant of the PT6 that was originally developed as a powerplant for the UAC TurboTrain power cars, but later developed as a stationary power generator and auxiliary power unit.
The ST6B-62 was a 550 brake horsepower (410 kilowatts) version of the PT6 developed for use in the STP-Paxton Turbocar, raced in the 1967 Indianapolis 500.[37]
STN 6/76
The STN 6/76 was a 500 brake horsepower (370 kilowatts) version of the PT6 developed for use in the Lotus 56, raced in the 1968 Indianapolis 500 and later in Formula One races, in 1971.[38][39]


The engine is used in over 100 different applications.








Engines on display[edit]

Specifications (PT6A-6)[edit]

Data from Jane's 62-63,[42]

General characteristics

  • Type: Turboprop
  • Length: 62 in (1,575 mm)
  • Diameter: 19 in (483 mm)
  • Dry weight: 270 lb (122.47 kg)


  • Compressor: 3-stage axial + 1-stage centrifugal flow compressor
  • Combustors: annular reverse-flow with 14 Simplex burners
  • Turbine: 1-stage gas generator power turbine + 1-stage free power turbine
  • Fuel type: Aviation kerosene to MIL-F-5624E / JP-4 / JP-5
  • Oil system: Split system with gear type pressure and scavenge pumps, with pressure to gearbox boosted by a second pump.


Gas Turbine Engines[43]
model stages[a] power SFC /h OPR dia. leng. weight applications
hp kW lb/hp g/kW lb kg
PT6A-21 3, 1 / 1, 1 550 410 0.63 380 19 in
48 cm
62 in
1.6 m
327 148 Beech Bonanza, King Air C90A/B/SE
PT6A-25 3, 1 / 1, 1 550 410 0.63 380 353 160 Beech T-34C
PT6A-25C 3, 1 / 1, 1 750 560 0.595 362 338 153 Embraer Tucano, Pilatus PC-7, PZL-130 Orlik
PT6A-27 3, 1 / 1, 1 715 533 0.603 367 289 131 Pilatus PC-6
PT6A-114/A 3, 1 / 1, 1 600–675 447–503 0.64 390 350 160 Cessna 208 Caravan
PT6A-135A 3, 1 / 1, 1 750 560 0.585 356 7 338 153 Cessna Conquest, Piper Cheyenne, Beech King Air F90
PT6A-42 3, 1 / 1, 2 850 630 0.601 366 8 66.9 in
1.70 m
403 183 Beech King Air 200/B200, C-12 Huron
PT6A-60A 4, 1 / 1, 2 1,050 780 0.548 333 8.5 72.5 in
1.84 m
487 221 Beech Super King Air 300/350
PT6A-64 4, 1 / 1, 2 700 520 0.703 428 8.5 70 in
1.8 m
456 207 Socata TBM 700
PT6A-66 4, 1 / 1, 2 850 630 0.62 380 9.5 456 207 Piaggio P.180 Avanti
PT6A-65B 4, 1 / 1, 2 1,100 820 0.536 326 74 in
1.9 m
481 218 Ayres Turbo-Thrush, PZL M28 Skytruck, Beech 1900/C
PT6A-67B 4, 1 / 1, 2 1,200 890 0.546 332 10.8 530 240 Pilatus PC-12
PT6A-67D 4, 1 / 1, 2 1,271 948 0.546 332 10.8 515 234 Beech 1900D
PT6A-68 4, 1 / 1, 2 1,250 930 0.54 330 72.2 in
1.83 m
572 259 Beech T-6 Texan II
PT6A-68B 4, 1 / 1, 2 1,600 1,200 0.54 330 575 261 Pilatus PC-21
PT6B-37A 3, 1 / 1, 1 900 670 0.584 355 19.5 in
50 cm
64.4 in
1.64 m
385 175 Agusta A119 Koala
PT6C-67A 4, 1 / 1, 1 1,940 1,450 0.47 290 22.5 in
57 cm
59.3 in
1.51 m
Bell/Agusta BA609
PT6C-67C 4, 1 / 1, 2 1,100 820 0.49 300 Agusta A 139
PT6T-3B/BF 2 × 3, 1 / 1, 1 1,800 1,300 0.6 360 43.5 in
110 cm
65.8 in
1.67 m
668 303 Bell 412/SP/HP/EP
PT6T-3D/DF 2 × 3, 1 / 1, 1 1,800 1,300 0.595 362 692–681 314–309 Bell 412/SP/HP/EP
PT6T-6 2 × 3, 1 / 1, 1 1,875 1,398 0.591 359 660 300 Bell 212, 412/SP/HP/EP, Sikorsky S-58T
PT6T-68 2 × 3, 1 / 1, 1 1,970 1,470 0.591 359 665 302 Bell 412HP
  1. ^ compressor / HP, LP turbine

See also[edit]

Related development

Comparable engines

Related lists


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