Page 5 - Volume 12 Number 8

An overlay of the PT6A-60A (red) and the -67A (blue) engines shows the extra length of the -67A that needed to be wedged into the same cowling as the original -60As. (COURTESY BLACKHAWK)
intake seal far enough aft to fully encase the air intake section of the longer -67A engine without requiring any associated exterior cowl modifications.
Exploring New Limits
More powerful engines are the obvious solution to boosting performance, but often more power comes with more weight, which can offset much of the power- driven gains. Not so with the XP67A upgrade. Yes, the -67A engine is heavier than the -60A; the reason for that is the extra length necessary to accommodate a fourth compressor stage (versus three stages in the -60A). It’s this extra stage of compression that is primarily responsible for pumping up the SHP capability from 1,050 (-60A) to 1,200 (-67A). However, the modification also includes swapping out the old 4-blade Hartzell metal props for 5-blade MT composite props. Not only do the lighter MT propellers offset the weight of the heavier engine, they offer many other advantages. In addition to their reduced vibration, noise and drag, they also offer unlimited blade life. Specific to the 350 installation, the MT props reduce the risk of foreign object damage
(FOD) due to their extra 2.6 inches of ground clearance. Additionally, the minimum idle speed limitation imposed on the Hartzells (due to resonance frequency issues) is eliminated with the MTs. Finally, let’s be honest, hanging those 5-bladed MT props on any airplane increases its ramp appeal by at least a factor of two!
While the -67A engine is rated at 1,200 SHP, to comply with the airframe limitation of the BE-300 series, the engine is flat rated back down to 1,050 SHP. Yet, with so much power in reserve, the XP67A 350 can maintain full power all the way to FL250 (a full 10,000 feet higher than the -60A). This provides a much quicker time- to-climb and more power on-hand at cruise altitude. A keen eye might notice the addition of a fixed flap just ahead of the oil cooler air discharge port on the bottom of each cowl. This flap enhances airflow through the oil coolers, increasing cooling efficiency. This is one of the major factors allowing the -67A to be operated at higher temperature limits than the -60A. Since the most common limiting factor on PT6 engines is Interstage Turbine Temperature (ITT), increasing those limits is more than just marketing fluff; it’s probably the single biggest reason the XP67A 350 has the fastest cruise speeds of any King Air variant.
The King Air used for this article’s flight evaluation was a 2003 model 350, recently converted to a XP67A 350 by Blackhawk.
AUGUST 2018 KING AIR MAGAZINE • 3