Loss of control in flight (stalls at low altitude), controlled flight into terrain (marginal weather), runway excursions, fuel mismanagement, engine failures, mid-air collisions. Human decision-making errors are the dominant factor. Staying proficient, current, and disciplined about personal weather minima is the best defence.
Instructor reduces power to idle at various phases: climb-out, circuit, at altitude. Key skills: immediate best glide speed, select suitable landing field, plan circuit to reach it, run emergency checklists (cause checks, restart, mayday call, passenger brief), execute approach. You practise but go around before landing. Tested on skill test.
Set conservative personal minima: visibility 8-10km (legal min 5km), cloud base 2,500-3,000ft AGL (legal can be 1,000ft), crosswind max 10-12kt (tested ~12-15kt). Avoid frontal weather, thunderstorms, forecast turbulence. Gradually reduce with experience (100+ hours). Weather-related accident rate is disproportionately high among low-hour pilots.