What should a pilot primarily rely on to maintain altitude during flight?

The primary instrument a pilot should rely on to maintain altitude during flight is the altitude indicator or altimeter. This device provides the pilot with critical information about their current altitude above sea level, allowing them to make precise adjustments to their flight path as necessary. The altimeter measures atmospheric pressure, converting this data into altitude readings. Maintaining a steady altitude is crucial for safe flight operations, especially in controlled airspace and during approaches and landings.

Using the altitude indicator ensures that the pilot can respond to changes in altitude due to factors such as air pressure variations, turbulence, or intentional altitude adjustments. This is vital for maintaining safety and compliance with air traffic control instructions. Other instruments, such as speed indicators or GPS navigation, while important for other aspects of flight management, do not directly provide information needed to maintain altitude. The fuel gauge is primarily used to monitor fuel levels and does not contribute to altitude control.