Pratt & Whitney Canada (P&WC) appears to be working on a successor to the best-selling PT6 turboprop engine it refers to as the PT9A-11 according to regulatory filings with the US Federal Aviation Administration.
As part ot the certification process, the engine maker on 17 May requested certain exemptions from the FAA for the powerplant, which it describes as a ”new centerline turbopropeller engine”.
Released by the US government’s online regulatory depository on 11 June, the filing says: “The PT9A-11 incorporates the latest best practices and lessons learned in the [high-pressure compressor] and [high-pressure turbine] stub shafts.”
P&WC did not immediately respond to requests for comment.
The filing asks the FAA to exempt the PT9A-11 from a certain FAA engine airworthiness standard.
“The exemption is in the public interest as it is an enabler for a new engine design which addresses safety, environmental, commercial considerations and benefits to the economy,” the filing says.
The document provides few details about the PT9A-11 and does not specify what type of aircraft the engine might power, but provides some clues.
In a section called “Benefits to economy”, P&WC writes, “The PT9A-11 model will ensure continued sales of one of the best-selling single-engine turboprop aircraft in its category”.
“The PT9A-11 engine model further extends one of the best-selling single-engine turbo-propeller engine model’s long history by remaining a competitive engine in the marketplace,” it adds.
P&WC has long produced the best-selling PT6, a 500-1,900shp (373-1,417kW)-class powerplant it calls “the world’s most-popular engine in its class”.
The engine maker introduced the PT6 in 1963 and has produced more than 64,000 of the engines. Such has been the PT6’s popularity and longevity that it equips a huge range of aircraft, notably including single-engined types as the Cessna 206B Caravan and Pilatus PC-12, a combined total of more than 4,600 of which are still in service, Cirium fleets data records.
The 17 May regulatory filing asks the FAA to exempt the PT9A-11 from an engine over-speed provision in the regulator’s airworthiness requirements. That provision specifies conditions under which “failure of a shaft section may be excluded from consideration in determining the highest over-speed that would result from a complete loss of load on a turbine rotor”.
P&WC wants the PT9A-11’s entire “[high-pressure] rotor shaft system” to be excluded, citing “the short distance between the [high-pressure compressor and high-pressure turbine] rotors and the limited numbers of torque carrying parts involved”.
The exemption would “allow the introduction of a new engine with lower fuel consumption”, the filing says.
Transport Canada has already approved an equivalent exemption for the PT9A-11, it adds.
