Commercial Pilot License (CPL) Practice Exam 2026 - Free Commercial Pilot License Practice Questions and Study Guide

The manual primer is crucial for ensuring a quick and efficient engine start, particularly in piston-engine aircraft. Its primary function is to inject fuel directly into the engine's cylinders before the start process. By manually priming the engine, pilots can ensure that there is enough fuel present to facilitate a smooth ignition when the engine is cranked. This is particularly important when starting a cold engine that may not have enough residual fuel from previous runs.

Having an adequate fuel charge enhances the likelihood of the engine starting quickly, reducing wear and tear, and minimizing the amount of time spent cranking the engine. In contrast, while other components like the fuel pump deliver fuel to the engine, their role is more about maintaining fuel flow during operation and not specifically targeted at the immediate starting process. Thus, the manual primer is essential for initiating the starting sequence effectively.