The NTSB has started investigating two fatal accidents that occurred over the weekend–one involving a Mitsubishi MU-2 and the other a Pilatus PC-12–and a serious crash of a Citation 560. The sole-occupant pilot of MU-2 N316PR was killed Sunday when the airplane crashed shortly after taking off from Fort Pierce, Fla., on an IFR flight plan to Murfreesboro, Tenn. A flight instructor and the new owner-pilot on board PC-12 N768H (registered on June 15) were killed Saturday when the turboprop single crashed five miles southeast of Big Timber Airport, Mont., shortly after takeoff during a training flight. Meanwhile, in another Saturday accident, the three people aboard Citation 560 N486SB were seriously injured when their twinjet crashed and burned while attempting to land at Cable Field, Upland, Calif., at about 10:30 p.m.