Installed in most modern aircraft cockpits, a heading indicator is a flight instrument designed to inform the pilot about which direction the aircraft is headed. A heading indicator is an advancement over the basic magnetic compass, and provides increased precision, improved reliability and an easy-to-read face. Many types of heading indicators exist with varying degrees of accuracy and cost; they range from basic vacuum-driven indicators to highly advanced, GPS-enabled indicators. A simple heading indicator requires readjustments every 10 to 20 minutes or so, while more sophisticated equipment, such as the heading indicators found on jet aircraft, use precision laser technology.
Generally speaking, heading indicators are round dials that represent north, south, east and west through the use of a 360° compass. For example, North would read as 360°, while East would read 90°. Aircraft must have a heading indicator installed and operating prior to flight in instrument conditions, though they are often optional during flight in clear weather. More sophisticated aircraft have heading indicators that integrate additional information such as navigational cues, terrain warning and air traffic alerts. Aircraft with global positioning system (GPS) technology often have the ability to overlay the proposed route of flight on the indicator's display.
A basic heading indicator is unable to determine direction on its own and requires the pilot to input the aircraft's initial direction when starting the airplane. Heading indicators make use of a gyroscope, a disc that rotates at very high speeds powered by the aircraft's vacuum system. Unfortunately, like any moving part, the heading indicator is subject to errors as a result of friction. As the gyroscope spins, it rubs against other parts inside the instrument, causing readings to lose accuracy over time and require corrective action by the pilot. More sophisticated heading indicators have eliminated this error by installing internal direction-finding equipment.
Benefits of a heading indicator over the traditional magnetic compass include increased situational awareness for the pilot, higher precision for long-distance navigation, and general ease of use. Magnetic compasses are often difficult to read and are only effective during straight and level flight, while heading indicators are capable of relaying accurate information at all times. It is important to note that, in most aircraft, the heading indicator is driven by the aircraft's vacuum system; if the system fails, so does the instrument. Negative aspects include increased maintenance costs, instrument errors, and the need for additional pilot training.