Understand engines, propellers and fuel

Each piston powerplant is a chain: fuel and air enter, combustion drives the pistons and crankshaft, and the propeller accelerates air to produce thrust. The engine also drives accessories, such as an alternator or a pump. Losing engine power may therefore affect more than propulsion. Engine indications help you work out which part of that chain has changed.

Compare left and right values only after considering commanded power, operating conditions and instrument meaning. Equal lever positions need not produce identical indications. During an abnormality, monitoring the operating engine matters too: it may be carrying more demand while cooling and temperature margins change.