Aircraft Clocks (Chronometer)

Whether called a clock or a chronometer, an FAA-approved time indicator is required in the cockpit of IFR-certified aircraft. Pilots use a clock during flight to time maneuvers and for navigational purposes. The clock is usually mounted near the flight instrument group, often near the turn coordinator. It indicates hours, minutes, and seconds.

For many years, the mechanical 8-day clock was the standard aircraft timekeeping device largely because it continues to run without electrical power as long as it has been hand wound. The mechanical 8-day clock is reliable and accurate enough for its intended use. Some mechanical aircraft clocks feature a push-button elapsed time feature. [Figure 1]

Aircraft Chronometer
Figure 1. A typical mechanical 8-day aircraft clock

As electrical systems developed into the reliable, highly redundant systems that exist today, use of an electric clock to replace the mechanical clock began. An electric clock is an analog device that may also have an elapsed time feature. It can be wired to the battery or battery bus. Thus, it continues to operate in the event of a power failure. Electric aircraft clocks are often used in multiengine aircraft where complete loss of electrical power is unlikely.

Many modern aircraft have a digital electronic clock with LED readout. This device comes with the advantages of low power consumption and high reliability due to the lack of moving parts. It is also very accurate. Solid-state electronics allow for expanded features, such as elapsed time, flight time that starts automatically upon takeoff, a stop watch, and memories for all functions. Some even have temperature and date readouts. Although wired into the aircraft’s electrical system, electronic digital clocks may include a small independent battery inside the unit that operates the device should aircraft electrical power fail. [Figure 2]

Aircraft Chronometer
Figure 2. A typical aircraft electronic clock

On aircraft with fully digital computerized instrument systems utilizing flat panel displays, the computer’s internal clock, or a GPS clock, can be used with a digital time readout usually located somewhere on the primary flight display.