Which of the following is NOT a general type of fuel quantity gauge?

The correct answer is the litmus indicator, as it is not a recognized type of fuel quantity gauge used in aviation fuel systems.

Fuel quantity gauges are essential for providing pilots with real-time information about the amount of fuel in the tanks. The sight glass is a direct, visual method of determining fuel levels, typically using a transparent tube to see the fuel level. Electrical fuel gauges use sensors to provide an electronic reading, often displayed on the cockpit panel. The Bourdon tube is a mechanical device that can measure pressure and is sometimes adapted for use in fuel quantity measurement.

However, a litmus indicator is not applicable in this context as it pertains to measuring pH levels in liquids rather than indicating fuel quantity. Understanding these different methods allows for better grasp of fuel management and reporting in aviation.