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

The tachometer gauge, which measures the engine's rotational speed (usually in RPM), is typically driven by mechanical means through the engine. This mechanical driving often utilizes a flexible shaft that connects the tachometer to the engine's crankshaft. As the engine rotates, the movement is transmitted to the tachometer, allowing it to display the RPM accurately.

The mechanical drive is favored in many aircraft due to its reliability and simplicity, which are crucial in aviation where precise engine performance monitoring is essential. By using direct mechanical connection, the tachometer can provide real-time engine speed data without delays that can occur in electric or hydraulic systems.

Other methods, such as electric or battery-operated systems, may be found in some modern aircraft, yet they are less traditional compared to the direct mechanical drive, hence the explanation for why the engine-driven mechanical option is correct.