In our series on refurbishing airplanes, we’ve examined what’s involved with updating all aspects of your airplane as well as helping it age gracefully. In this article, we turn to breathing new life into an existing airframe by adding more power to get more performance. We’re looking at one of the more exciting upgrades currently in development—Blackhawk Modifications, Inc. of Waco, Texas is flight testing its upgrade to the King Air 350 that’s designed to give it cruise speeds that will match a number of jets.
When our editorial director Paul Bertorelli was researching his article on PT-6 overhauls that appeared in the October 2015 issue of our sister publication Aviation Consumer, he was repeatedly advised by PT-6 operators, sales professionals and shops to look at the engine upgrade conversions Blackhawk offered for King Airs, Piper Cheyennes, the Cessna Conquest I and Caravan. What he found was that customers brought in their run-out PT6 engines and exchanged them for factory-new ones that with more power and greater efficiency. The new engines are flat rated to the same SHP as the old engines, but are able to deliver that power to much higher altitudes, providing faster climbs and cruise speeds.
That approach is behind what Blackhawk is calling the XP67A Engine Upgrade. It’s hanging a pair of Pratt and Whitney Canada PT6A-67A engines on the standard King Air 350 in place of its current PT6A-60A powerplants. That means increasing thermodynamic shaft horsepower from 1050 to 1200 per side. The -67A engines will be flat rated to 1050 SHP to match the airframe limit of the airplane, however, because of flat rating, they will be able to maintain that 1050 SHP to much higher altitudes boosting rates of climb and cruise speeds.
The prototype airplane is presently undergoing flight testing, with Blackhawk predicting that it will receive the necessary Supplemental Type Certificate for the mod from the FAA by the end of June 2017. Blackhawk is reporting that performance to date has exceeded expectations with climbs demonstrated from sea level FL350—the maximum operating altitude—in as little as 18 minutes, less than half the time required by the unmodified King Air 350. Blackhawk is also reporting that cruise speeds as high as 340 knots have been observed to date. Blackhawk’s president Jim Allmon said that the “XP67A will attain jet-like speeds, can carry twice the payload much farther, and will burn a fraction of the fuel while lowering maintenance, operating and acquisition costs. It reintroduces the King Air 350 to a larger group of private, business and commercial operators as well as the special missions area.”
To convert the additional power into thrust, a five-blade MT prop with a 102-inch diameter has been married to the PT6A-67A engine. The prop blades have an unlimited life, are field repairable and have nickel alloy leading edges for erosion protection. A part of the mod involves removing the ground RPM restrictions and the ground idle solenoid to provide smoother taxi operations. Blackhawk said that the MT props add to the performance gain from the higher horsepower engines and reduce overall noise emissions and vibration. We’ve observed those results with MT propellers on other aircraft mods. Blackhawk said that it is also working to certify a five-blade Hartzell composite propeller with the STC and that Raisbeck Engineering is working to upgrade its four-blade aluminum propeller to be compatible with the XP67A upgrade.
Blackhawk is planning to obtain the STC for the XP67A upgrade for all King Air 350s equipped with Proline II with round gauges and is working with Garmin to include G1000-equipped airplanes as well. It is pursuing a separate certification program for a gross weight increase to 16,500 pounds with extended range fuel tanks and to include the Proline 21 avionics package.
We’ll be following the development of the XP67A mod with interest to see if it proves as successful in increasing the King Air 350’s performance as other Blackhawk upgrades have been on PT6A-equipped airplanes.
Rick Durden is the features editor of AVweb and the author of The Thinking Pilot’s Flight Manual or, How to Survive Flying Little Airplanes and Have a Ball Doing It, Vols. 1 & 2.