What is the main difference between a hot start and a normal start in aircraft?

The main difference between a hot start and a normal start in aircraft engines pertains to the conditions of the engine and the procedures used to initiate engine operation. In a hot start situation, the engine is already warm, typically after being shut down for a short period. Due to the heat in the engine, the fuel in the combustion chamber may vaporize easily, leading to the possibility of a rich fuel-air mixture. Hence, priming, which adds additional fuel to the combustion chamber to enhance starting, is generally not necessary or may even hinder starting due to the already favorable starting conditions.

In contrast, during a normal start, the engine may be cold, and priming is often essential to ensure that there is enough fuel in the combustion chamber for a successful start. Proper starting procedures in this context involve checking various aspects of the engine to ensure safety and effectiveness.

This understanding of the hot start procedure allows pilots to optimize the starting process, minimizing potential issues associated with excessive fuel in the engine during startup.