From Avbuyer :
beech pd290 by David Ross, on FlickrFurther Development
A fifth King Air model was announced a year later – the B100. This would be the first- and ultimately the only production King Air to be powered by an engine other than the Pratt & Whitney PT6A. The B100 featured a Garrett AiResearch TPE-331 turboprop.
Beech’s intentions with the B100 were again two-fold: They wanted to expand the King Air family’s range in the market; and they wanted to reduce their dependence on a single supplier for their best-selling product.
The B100 made its first flight on March 20- 1975.
Eight days earlier- on March 12- Beech Aircraft began flight tests on still another new model of the King Air. This one had Pratt & Whitney engines- but they weren’t PT6 turboprops; they were JT-15D fanjets.
Between March 1975 and September 1977- Beech conducted 103 test flights of the jet powered King Air it called PD 290. The PD stood for Preliminary Design. The airframe was essentially a Model 200- with jet engines mounted where the turboprops would have been.
The NACA 23000-series airfoil used on the King Air was designed for optimal performance in the low- to mid-airspeed ranges- and with jet power it produced a lot of drag. As a result- the jet-powered King Air proved disappointingly slow.
With turboprops outselling jets in the market by a rate of 7 to 3 at that time- Beech management elected to leave the jet market to other manufacturers and instead concentrate their efforts on the turboprop airplane for sale market.