Most VFR into IMC accidents occurred under which condition?

The correct answer highlights that most VFR (Visual Flight Rules) into IMC (Instrument Meteorological Conditions) accidents happened when no flight plan of any kind was filed. This situation often leads to greater risk because pilots flying under VFR are not in direct communication with air traffic control (ATC) when they do not file a flight plan. Without ATC awareness of the flight's parameters and potential deviations, especially as weather conditions deteriorate, the pilot may inadvertently navigate into IMC conditions without timely assistance or guidance.

Additionally, filing a flight plan helps outline the intended route and can enhance safety by ensuring that search and rescue efforts can be initiated more promptly should an accident occur. Without this proactive measure, the chances of a VFR pilot becoming disoriented and encountering IMC conditions increase significantly, leading to dangerous scenarios.

In contrast, other conditions such as flying with an instructor, when under autopilot, or during night flying do not inherently correlate to the frequency of these accidents as strongly as the lack of a flight plan. These circumstances may pose risks, but they do not have the same glaring implications for situational awareness and emergency response as not filing a flight plan does.