On my 3rd flight, the aircraft (COA 737-700 2D panel only) rapidly decended from FL390 and impacted the ground in a vertical dive. A/C had completed 3 hours of a 4 hour flight (KIAH-KSFO) and had just entered the Modesto Two Arrival into KSFO. A/C had just completed a 64 degree left turn over OAL VOR. Bank angle went to 80 degrees prior to dive. A/C was in LNAV mode only with AP set at M.82 and FL390. Disconnecting the AP did nothing to help control the A/C. The FMC had been programmed according to the Beginners FMC Tutorial and had worked properly up to the incident.I have absolutely NO clue as to what happened here. But, if I spend 3 hours in a flight only to have the A/C crash, that A/C is not going to be used again until I find out............For what it's worth. This was my first crash in over 4 years of FS flying.Anyone else experience this?

Yes!While flying an EZY B737 3D panel. The aircraft was turning and lining up for a standard runway 24L arrival, descending though 4,200ft heading towards LEPA after an hours flight from EGKK.While the aircraft was turning the nose pitched down (very hard)... I waited for the autopilot to compensate for this error, but it did not. At one point the aircraft was 'falling' though the air at 3,900ft per minute. I disengaged the Auto Pilot and managed to level the aircraft. After flying for a further ten minutes I made an emergency landing, with no other problems.After going though the FMC and looking at the aircrafts systems I could not find any abnormalities. Because of this I flew back to Luton (EZY