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

During an engine failure, it is crucial to maximize the aircraft's performance during the glide phase. Setting the fuel mixture to full rich is appropriate in this situation for several reasons.

First, a full rich mixture ensures that the engine receives the maximum amount of fuel possible. In the event of an engine failure, maintaining as much power as can be achieved — even if the engine is not functioning at full capacity — can help optimize glide performance and maintain control of the aircraft.

Secondly, if there is a chance of restarting the engine during the glide, having the mixture set to full rich supplies the necessary fuel for ignition, should conditions permit a successful restart. It's also important because, during an emergency descent, the engine may be needed again as a backup, thus ensuring the correct fuel mixture is vital.

Other mixture settings, such as lean or idle cut-off, would reduce the fuel supply to the engine or prevent combustion altogether, which can lead to difficulties in controlled descent and lessening the chances of successfully reigniting the engine.