From Legacy to Leading Edge:

The Pratt & Whitney Canada PT-6 turboprop engine turns 50

In aviation maintenance jargon, the term “aircraft quality” usually describes something that works the first time, every time, and lasts a long time.” This definition would certainly apply to the Pratt & Whitney Canada (P&WC) PT-6 turboprop engine. The PT-6 core engine could be the icon for “Aircraft Quality.”

In May 2010, P&WC chose the prestigious setting of the European Business Aviation Convention and Exhibition (EBACE) in Geneva, Switzerland, to celebrate 50 years of service and recognize the contribution the PT-6 engine has made to the company and the aviation industry at large. P&WC began designing and developing the PT-6 in the mid-‘50s. On May 30, 1961, the prototype was mounted on a Beech 18 at de Havilland’s Downsview facility for its test flight. The PT-6 performed as advertised and the first production engine PT-6A S/N 20001 was delivered to Beech on Dec. 22, 1963.

To appreciate the PT-6 story you have to understand the company that builds it. P&WC is a company that is in a continuous state of innovation and transition, focusing on improving core products while pushing research and development. In the 1930s it was servicing the Canadian bush flying business. In the 1940s it was heads down producing and servicing the radial engines used to power the Allied Army and Air Force aircraft. After the war ended it moved into peace-time manufacturing, and in a few short years had made the exponential transition from radial piston to gas turbine engines.

P&WC now has a true global footprint. According to current P&WC president John Saabas, “Somewhere in the world a P&WC-powered aircraft takes off or lands every second. “P&WC engines power the largest fleet of business and regional aircraft and helicopters. They have 10,000 operators and 700+ airlines in more than 198 countries.”

Success of PT-6

On Oct. 20, 2009, P&WC announced that it had delivered its 70,000th engine (a PT-6A-60A turboprop delivered to Hawker Beechcraft Corporation and installed on a King Air 350). Why has P&WC become a global leader when so many other aviation companies have struggled, merged, or failed? In my opinion, it was the beloved PT-6, that backward-mounted turbine engine that is admired by owners, operators, pilots, and maintenance techs alike. According to P&WC, it has delivered more around “46,000 PT-6 and today 26,000 of those engines are still flying.”

What made the PT-6 so successful? Its simple straightforward design. It is reliable, dependable, and easy to manufacture and maintain. It has two independent turbines; one driving a compressor in the gas generator section, the second driving reduction gearing for the propeller.

The core turbine engine consists of two sections that can be easily separated for maintenance. The compressor and power turbines are located in the approximate center of the engine with their shafts extending in opposite directions. This provides for simplified installation and inspection procedures. A two-stage planetary gearbox is located in the front of the engine and provides the speed reduction between the power turbine and the propeller shaft. An accessory gear case is located at the rear of the engine with the relevant accessory drives and mounting pads. The larger PT-6A models get their increase in horsepower from an additional four-stage axial configuration.

PT-6A engines are available in more than 65 models ranging in power from 500 to over 2,000 shaft horsepower. They come in three basic sizes — small, medium, and large. The small (PT-6A-11 to A-36) delivers 500 to 750 shaft horsepower and measures 25” H x 21.5” W x 62” L. The medium (PT-6A-38 to A-45R) delivers 700 to 1,200 shaft horsepower and measures 22” H x 19.5” W x 67 to 72” L. The large (PT-6A-52 to A-68) delivers 1,050 to 1,700 shaft horsepower and measures 22” H x 19.55” W x 67 to 76” L. The ubiquitous PT-6s are currently powering about 100 diverse aircraft types. Some example are: the Beechcraft King Air, Cessna 208 Caravan, de Havilland Canada Dash 7, Piaggio P180 Avanti, Bell/Agusta BA609, and the Sikorsky S-76B.

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