What can cause an aircraft to plummet from high altitude in an uncontrollable way?
A selection of accidents come to my mind.
One tragic accident was Indonesia AirAsia Flight 8501, Airbus A320-216 in December 2014. Here a malfunction in the rudder control system was reacted to by the crew in an inappropriate way. This fatal accident was put down to pilot error. That is mishandling after an aircraft system failure leading to a stall and plunge into the sea.
The loss of control and crash of Alaska Airlines Flight 261 McDonnell Douglas MD-83 in January 2000 is different from the recent Boeing 737 fatal accident but it warrants inspection. For a start the MD-80 series has a high tail and rear engines. However, Flight 261 had a highly experienced crew, but the failure of a critical control component meant the aircraft became unrecoverable. Also, the MD-80 series of aircraft is of a similar generation to the Boeing 737. For both aircraft types, the control of the horizontal stabilizer is necessary to maintain safe flight. The MD-60 accident involved a catastrophic loss of pitch control.
Looking at the sequence of the fatal accident of SilkAir Flight 185, Boeing 737-300, in December 1997 it has some similarities. The lead investigators were unable to determine the cause, but suspicion fell on the aircraft rudder controls. This accident remains controversial. The accident flight recorders either stopped because wires broke or because their power was wilfully disconnected. We will never know which was the case.
Again, an accident with an inconclusive report is that of the uncontrolled descent and crash of United Airlines Flight 585. Boeing 737-200, March 1991. Anomalies were identified in the accident airplane’s rudder control system, but the accident was not attributed to these problems.
As can be seen from this small sample of accidents the interaction between aircraft and crew, when a control system failure occurs is a matter of great interest.