"N502BD" ran into problems of its own. Early models used a variable speed belt drive system to transfer power from the engine to the propeller shaft. This was removed from "N502BD" and it suddenly began exhibiting a serious vibration problem during taxi tests. Experts were called in, and a freewheel clutch and additional bearings added to correct the problem, but it was not until March 26, 1973 that "N502BD" flew. From then on the test program seemed to go more smoothly, although this aircraft also suffered two dead stick landings, one from a pinched fuel line occurred while the plane was being observed by the "Popular Science" author, and another due to metal in a new engine's cylinder.